1 00:00:00,506 --> 00:00:06,156 [ Silence ] 2 00:00:06,656 --> 00:00:07,636 >> Welcome back. 3 00:00:08,386 --> 00:00:10,956 First thing first, we have a new team member, 4 00:00:10,956 --> 00:00:12,246 Chris Gerber [assumed spelling]. 5 00:00:12,246 --> 00:00:14,516 So, some of you probably already heard from him 6 00:00:14,516 --> 00:00:21,646 as he being your point person, but he's here to help. 7 00:00:21,646 --> 00:00:25,096 Second, don't forget that your project is due next Wednesday. 8 00:00:25,366 --> 00:00:30,676 So we are diving into iOS/Objective-C today. 9 00:00:31,056 --> 00:00:34,266 But you still need to keep up with your project that still has 10 00:00:34,266 --> 00:00:35,756 to do with the JavaScript and HTML. 11 00:00:36,446 --> 00:00:40,036 OK. So, first we're going to recommend some books. 12 00:00:40,646 --> 00:00:42,516 David always recommends this one. 13 00:00:42,516 --> 00:00:45,816 You're going to want to make sure that your book is 14 00:00:45,816 --> 00:00:48,106 up to date with all the new iOS versions. 15 00:00:48,376 --> 00:00:52,686 So iOS 7, it was a very recent development. 16 00:00:52,686 --> 00:00:55,066 We are only going to be be dealing with iOS 6, 17 00:00:55,066 --> 00:00:56,336 plus I think iOS 7 isn't 18 00:00:56,336 --> 00:00:59,836 like officially available for couple of months. 19 00:00:59,836 --> 00:01:02,746 So, iOS 6 is what you're going to want to be using. 20 00:01:03,056 --> 00:01:05,436 When you start going back versions of iOS, 21 00:01:05,726 --> 00:01:07,596 things start changing pretty significantly. 22 00:01:07,596 --> 00:01:10,736 You don't want to go back to like iOS 4 before 23 00:01:10,736 --> 00:01:12,406 because things are going to be substantially different. 24 00:01:12,876 --> 00:01:14,776 So, look for iOS 6 things. 25 00:01:15,196 --> 00:01:17,856 Another book that I've never looked at 26 00:01:17,856 --> 00:01:22,516 but is supposedly also pretty good is this one. 27 00:01:22,516 --> 00:01:25,336 And I added this slide just before 28 00:01:25,336 --> 00:01:27,876 because this is one the actually use just 29 00:01:27,876 --> 00:01:29,426 to catch myself up with everything. 30 00:01:30,526 --> 00:01:34,916 It's a pre-preview of a book and I found it to be pretty good. 31 00:01:35,206 --> 00:01:38,626 I feel obligated to say like he does at the top of the page 32 00:01:38,626 --> 00:01:40,106 like if you find it useful you might want 33 00:01:40,106 --> 00:01:41,876 to consider actually buying the book. 34 00:01:42,506 --> 00:01:46,746 But that pretty much everything is in here. 35 00:01:46,896 --> 00:01:49,556 OK. So before we get into Objective-C, you first need 36 00:01:49,556 --> 00:01:53,116 to touch on C. So, it's important to remember 37 00:01:53,116 --> 00:01:57,156 that Objective-C is a proper super set of regular C. 38 00:01:57,446 --> 00:01:59,966 So like any Objective-C program that you write, 39 00:01:59,966 --> 00:02:03,496 you could write valid C all throughout the 40 00:02:03,496 --> 00:02:04,336 Objective-C program. 41 00:02:04,416 --> 00:02:05,696 We're not literally everywhere. 42 00:02:06,206 --> 00:02:08,196 But everything you know 43 00:02:08,196 --> 00:02:10,696 from C is still applicable in Objective-C. 44 00:02:10,836 --> 00:02:15,436 So, first, show of hands, who know C or any C? 45 00:02:15,436 --> 00:02:19,186 All right, that's better than I was anticipating. 46 00:02:19,596 --> 00:02:23,256 And another show of hands, who has any experience 47 00:02:23,256 --> 00:02:25,296 with any object-oriented language? 48 00:02:25,796 --> 00:02:27,456 All right. 49 00:02:28,606 --> 00:02:32,816 Cool. So, we'll do a really quick intro to C just 50 00:02:32,816 --> 00:02:34,096 to refresh you on everything. 51 00:02:34,096 --> 00:02:38,006 You'll probably recognize that a lot of it is pretty similar 52 00:02:38,006 --> 00:02:40,846 to JavaScript, so probably still pretty fresh. 53 00:02:42,086 --> 00:02:45,086 So, your very standard "Hello World" program. 54 00:02:45,766 --> 00:02:49,036 What does hash includes, standard IO.H2. 55 00:02:49,036 --> 00:02:50,396 What is standard IO.H? 56 00:02:51,331 --> 00:02:53,331 [ Pause ] 57 00:02:53,646 --> 00:02:55,246 I Think I might have heard someone say. 58 00:02:55,246 --> 00:02:56,706 But it's a header file. 59 00:02:56,896 --> 00:02:59,446 It literally just contains like-- 60 00:03:00,106 --> 00:03:04,466 we'll see like the declarations of the functions. 61 00:03:04,776 --> 00:03:06,426 So we'll see more examples of those later. 62 00:03:06,426 --> 00:03:09,746 Those are still going to be pretty important in Objective-C.œ 63 00:03:10,336 --> 00:03:12,746 Here we see, we are declaring a main function. 64 00:03:12,746 --> 00:03:14,566 So just like in C we declare a main function, 65 00:03:14,566 --> 00:03:17,116 in Objective-C you are also going to have a name function. 66 00:03:17,856 --> 00:03:23,526 And what are these guys, int argc and con char star argv? 67 00:03:23,526 --> 00:03:26,546 What are those? 68 00:03:26,766 --> 00:03:27,666 Command line arguments. 69 00:03:27,986 --> 00:03:31,426 So int argc is how many arguments were passed 70 00:03:31,426 --> 00:03:34,656 at the command line and con char star argv are-- 71 00:03:34,656 --> 00:03:36,436 what those arguments were. 72 00:03:37,176 --> 00:03:39,656 And then we just printf, will be-- 73 00:03:39,656 --> 00:03:41,016 we'll see that once we got to Objective-C. 74 00:03:41,016 --> 00:03:43,076 We're not going to be really using printf anymore, 75 00:03:43,536 --> 00:03:45,606 but pretty standard program. 76 00:03:46,966 --> 00:03:49,696 So statements-- that is a statement. 77 00:03:50,876 --> 00:03:54,316 Variables, you just declare them int n or say int n equal 0. 78 00:03:54,316 --> 00:03:57,256 That's going to be the same when we get to Objective-C. 79 00:03:57,576 --> 00:04:00,486 We have all of our regular primitive date types, char, 80 00:04:00,486 --> 00:04:05,356 double float, int long, and then the modifiers like unsigned int 81 00:04:05,356 --> 00:04:08,756 and unsigned double, and printf. 82 00:04:09,326 --> 00:04:14,336 So, if we-- let's go into-- 83 00:04:15,576 --> 00:04:17,836 We'll have a whole bunch of example programs up. 84 00:04:18,896 --> 00:04:21,876 And we have a whole bunch in C and Objective-C. 85 00:04:21,876 --> 00:04:24,866 We're not going to go through all of the C ones because a lot 86 00:04:24,866 --> 00:04:26,046 of them will just be tedious. 87 00:04:26,386 --> 00:04:28,986 But if you feel you need a refresher, you can just go back 88 00:04:28,986 --> 00:04:29,846 and look at all these. 89 00:04:30,426 --> 00:04:34,956 So, we'll look first C one, hello C. 90 00:04:35,516 --> 00:04:38,956 [ Pause ] 91 00:04:39,456 --> 00:04:43,676 OK. So, this is what we just saw before up there. 92 00:04:44,206 --> 00:04:45,566 And printf, remember, 93 00:04:45,676 --> 00:04:48,806 takes these modifiers such as percent S. 94 00:04:49,516 --> 00:04:52,416 [ Pause ] 95 00:04:52,916 --> 00:04:57,886 That are going to then be a comma separated list of things 96 00:04:57,886 --> 00:05:00,206 at the end of the printf call that you're going to fill in. 97 00:05:00,506 --> 00:05:02,986 So like percent S, it's expecting a string to fill 98 00:05:02,986 --> 00:05:06,696 in that percent S. And if instead we did int n equals 50, 99 00:05:07,366 --> 00:05:11,886 then we could do percent D and pass in the variable N. 100 00:05:12,316 --> 00:05:15,056 So that's how we're going to use printf with-- 101 00:05:15,056 --> 00:05:18,296 that's how we print variables. 102 00:05:18,666 --> 00:05:22,626 And you'll see that these format specifiers just percent S 103 00:05:22,626 --> 00:05:24,326 and S percent D for integer. 104 00:05:25,216 --> 00:05:28,706 Those are going to carry over into some Objective-C areas. 105 00:05:29,516 --> 00:05:34,576 [ Pause ] 106 00:05:35,076 --> 00:05:37,336 Plus, all of these primitive data types, remember, 107 00:05:37,336 --> 00:05:41,566 that Objective-C is a super set of C, these still exist. 108 00:05:42,016 --> 00:05:43,106 [ Inaudible Remark ] 109 00:05:43,106 --> 00:05:43,236 Yeah? 110 00:05:43,236 --> 00:05:44,706 >> Do we still we have link to the book, the increment book? 111 00:05:47,016 --> 00:05:48,266 [ Inaudible Remark ] 112 00:05:48,266 --> 00:05:49,856 >> The slide will be online later. 113 00:05:49,856 --> 00:05:51,086 But if you want to look it up now-- 114 00:05:51,836 --> 00:05:52,976 >> Thank you. 115 00:05:53,206 --> 00:05:56,426 >> Yeah. And feel free to stop me at any point with questions. 116 00:05:57,516 --> 00:06:14,156 [ Pause ] 117 00:06:14,656 --> 00:06:15,196 It's good. 118 00:06:15,766 --> 00:06:17,096 Oh, yeah. OK. 119 00:06:19,096 --> 00:06:24,636 So the Boolean expressions, the very simple ones 120 00:06:24,636 --> 00:06:26,536 that you should-- all be used to at this point. 121 00:06:27,356 --> 00:06:29,786 Conditions, we have a regular if-elses. 122 00:06:29,786 --> 00:06:31,836 Loops, we have for loops. 123 00:06:31,836 --> 00:06:36,116 So in JavaScript, you also have the, like, for in. 124 00:06:36,286 --> 00:06:38,176 You'll also see that in Objective-C. 125 00:06:38,206 --> 00:06:39,666 Regular C doesn't' have that. 126 00:06:39,826 --> 00:06:41,866 So we have a regular for loop, 127 00:06:41,866 --> 00:06:43,836 regular while loop, regular do-while. 128 00:06:44,266 --> 00:06:47,436 And all of those will still be usable in Objective-C. 129 00:06:47,706 --> 00:06:52,216 So, casting is an interesting case where it's exactly the same 130 00:06:52,216 --> 00:06:53,656 between C and Objective-C. 131 00:06:53,886 --> 00:06:55,976 You're going to see, you might be needing it a lot more once 132 00:06:55,976 --> 00:06:57,036 you get to Objective-C. 133 00:06:57,366 --> 00:07:02,506 So, in C, there are only so many cases I can possibly think 134 00:07:02,506 --> 00:07:03,646 of where it wants a cast. 135 00:07:04,026 --> 00:07:07,576 Like one example is if I want to do like 3 divided by 5. 136 00:07:07,906 --> 00:07:10,346 You know, how like if we just do the integers then 3 divided 137 00:07:10,346 --> 00:07:11,786 by 5 is going to be 0. 138 00:07:12,086 --> 00:07:14,976 So I might want to cast 3 to a float so that it actually does 139 00:07:14,976 --> 00:07:16,636 like floating point division. 140 00:07:16,956 --> 00:07:19,896 So that's one scenario I can think of where I want to cast. 141 00:07:19,936 --> 00:07:22,576 Once we get to Objective-C and we start dealing with classes 142 00:07:22,576 --> 00:07:26,646 and things, then we're going to want to cast like we'll see more 143 00:07:26,646 --> 00:07:28,396 of this but like supertypes to subtypes 144 00:07:28,396 --> 00:07:29,856 and subtypes to supertypes. 145 00:07:30,196 --> 00:07:34,006 So casting, you'll want to be comfortable with it. 146 00:07:34,476 --> 00:07:42,236 And then Pointers, they won't be as important in Objective-C 147 00:07:42,236 --> 00:07:44,616 but you're still going to have to deal with them. 148 00:07:44,616 --> 00:07:49,706 So, we have just the type of a pointer-- 149 00:07:49,836 --> 00:07:50,976 let's actually look just an example. 150 00:07:51,516 --> 00:07:56,386 [ Pause ] 151 00:07:56,886 --> 00:07:57,236 All right. 152 00:07:57,236 --> 00:08:01,666 We'll go over the typical example of a swap function. 153 00:08:02,446 --> 00:08:04,446 [ Pause ] 154 00:08:04,876 --> 00:08:06,976 That's here. 155 00:08:07,046 --> 00:08:10,226 Oh. So this line, like, hint 156 00:08:10,226 --> 00:08:14,896 to that before is swap line is the function's prototype. 157 00:08:15,316 --> 00:08:18,006 So those are the sort of things that we'll see in header files 158 00:08:18,006 --> 00:08:23,016 like standard IO.H. We'll also see like struct definitions. 159 00:08:23,016 --> 00:08:23,926 We'll get to structs. 160 00:08:24,316 --> 00:08:26,226 We'll see hash define things. 161 00:08:28,336 --> 00:08:33,416 So, here in main, we declare variable X and variable Y, 162 00:08:33,416 --> 00:08:37,746 and then we print X, print Y. And now we want to swap X and Y. 163 00:08:38,126 --> 00:08:42,166 So ideally, after this swap line, X will have the value 1 164 00:08:42,166 --> 00:08:43,496 and Y will have the value 0. 165 00:08:43,626 --> 00:08:44,816 They will have swap values. 166 00:08:45,746 --> 00:08:48,016 And I won't actually run it. 167 00:08:48,306 --> 00:08:51,596 But trust me when I say that this will not succeed. 168 00:08:51,986 --> 00:08:55,756 Looking at the actual swap function, we see it takes A 169 00:08:55,786 --> 00:09:01,506 and B, so we're passing X for A and Y for B. We then store A 170 00:09:01,506 --> 00:09:05,526 in a temporary variable, put B into A, and put the original A 171 00:09:05,526 --> 00:09:10,366 into B. So, why this doesn't work is it's important 172 00:09:10,366 --> 00:09:12,596 to remember that everything in C 173 00:09:12,936 --> 00:09:15,466 when you pass its way function it's always a copy 174 00:09:15,466 --> 00:09:16,566 of the thing being passed. 175 00:09:17,136 --> 00:09:20,646 And so here, what we're actually passing to a swap is a copy 176 00:09:20,646 --> 00:09:23,056 of the value 0 and the copy of the value 1. 177 00:09:23,626 --> 00:09:27,476 And so down in the swap function when we say A equals B, 178 00:09:27,606 --> 00:09:30,946 we're just modifying the copy of those values. 179 00:09:31,016 --> 00:09:35,176 We're not modifying the original X and Y. So here's 180 00:09:35,176 --> 00:09:36,746 where pointers become important. 181 00:09:37,516 --> 00:09:50,756 [ Pause ] 182 00:09:51,256 --> 00:09:55,336 So, here, notice the function prototype is changed. 183 00:09:55,946 --> 00:10:00,146 We now are passing int star A. So as soon as you see int star 184 00:10:00,146 --> 00:10:01,756 or char star, anything star, 185 00:10:01,756 --> 00:10:03,086 you know you're dealing with a pointer. 186 00:10:04,356 --> 00:10:05,976 And it's coming down here. 187 00:10:05,976 --> 00:10:09,606 We're no longer passing X and Y. We're passing ampersand X 188 00:10:09,606 --> 00:10:12,476 and ampersand Y. So ampersand, 189 00:10:12,476 --> 00:10:16,256 I usually read literarily as address of. 190 00:10:16,456 --> 00:10:19,706 So we're passing the address of X and we're passing the address 191 00:10:19,706 --> 00:10:26,526 of Y. And so-- Oh, and it's-- since X is an int, 192 00:10:27,056 --> 00:10:29,156 then when you get the address of an int, 193 00:10:29,636 --> 00:10:32,356 the type of that address is an int star. 194 00:10:32,766 --> 00:10:34,806 We had a char and-- with an ampersand before it, 195 00:10:34,806 --> 00:10:36,006 then we would have a char star. 196 00:10:36,556 --> 00:10:40,736 So coming down into the swap function, again, this is going 197 00:10:40,736 --> 00:10:42,856 to take an int star and an int star. 198 00:10:43,276 --> 00:10:47,566 And here, it's unfortunately somewhat confusing 199 00:10:47,566 --> 00:10:50,276 that there are two uses for the star. 200 00:10:50,896 --> 00:10:52,546 The first use for the star is 201 00:10:52,546 --> 00:10:54,146 to declare something as a pointer type. 202 00:10:54,566 --> 00:10:55,966 So when you see int star B, 203 00:10:55,966 --> 00:10:59,096 you know that B is a pointer to an integer. 204 00:10:59,646 --> 00:11:02,556 When you do not see a type, like right here, when you say star A, 205 00:11:02,726 --> 00:11:05,086 we are de-referencing that pointer. 206 00:11:05,606 --> 00:11:12,176 So if B points to Y and A points to X, 207 00:11:12,556 --> 00:11:18,416 then star A is referencing the original X. And so temp is going 208 00:11:18,416 --> 00:11:22,696 to store the original value of X. Star A equals star B, 209 00:11:22,956 --> 00:11:25,516 we're going to go to the original value of X, 210 00:11:25,516 --> 00:11:27,586 like the original X and we're going 211 00:11:27,586 --> 00:11:30,566 to store there the original Y. And so, 212 00:11:30,566 --> 00:11:32,516 X is actually been changed now. 213 00:11:32,886 --> 00:11:35,316 And here, we're doing the same thing. 214 00:11:35,316 --> 00:11:40,686 We're going to Y and storing the original value of X. Questions? 215 00:11:41,451 --> 00:11:43,451 [ Pause ] 216 00:11:43,886 --> 00:11:48,126 OK. So, in Objective-C, a lot of this is going to be-- 217 00:11:48,816 --> 00:11:52,466 you won't be needing to do as many explicit de-references. 218 00:11:52,826 --> 00:11:53,796 But it's important to remember 219 00:11:53,796 --> 00:11:55,476 that when you're passing these things 220 00:11:55,716 --> 00:11:58,706 that object themselves are pretty much like pointers. 221 00:11:59,136 --> 00:12:03,186 And so if like you're passing object to a function and in 222 00:12:03,186 --> 00:12:04,836 that function you modify the object, 223 00:12:05,116 --> 00:12:06,866 the original object will had been modified 224 00:12:07,196 --> 00:12:07,956 and we're going to see that. 225 00:12:08,516 --> 00:12:15,736 [ Pause ] 226 00:12:16,236 --> 00:12:17,736 And just for fun, I threw in the end 227 00:12:17,736 --> 00:12:20,876 that char star star is also an example of a pointer. 228 00:12:21,246 --> 00:12:23,676 It just happens to be a pointer that points 229 00:12:23,676 --> 00:12:26,186 to a pointer that points a char. 230 00:12:27,336 --> 00:12:34,276 So a good example of that is just our command line arguments, 231 00:12:34,626 --> 00:12:35,316 argv. 232 00:12:35,716 --> 00:12:40,746 So, ignoring the fact that it's bracket syntax, there are some-- 233 00:12:40,966 --> 00:12:42,356 this isn't entirely true. 234 00:12:42,606 --> 00:12:43,926 But in a lot of scenarios, 235 00:12:43,926 --> 00:12:46,306 arrays and pointers are pretty much equivalent. 236 00:12:46,606 --> 00:12:49,876 So con char star argv bracket, we could have also said 237 00:12:49,876 --> 00:12:53,466 as con char star star argv, which makes sense 238 00:12:53,466 --> 00:12:57,396 since argv is an array of strings 239 00:12:57,826 --> 00:13:01,576 and we represent a string as a pointer to a single character. 240 00:13:03,156 --> 00:13:03,966 Questions? 241 00:13:04,516 --> 00:13:13,506 [ Pause ] 242 00:13:14,006 --> 00:13:19,206 OK. So, structs, so it'll be important 243 00:13:19,206 --> 00:13:20,316 to actually remember structs 244 00:13:20,866 --> 00:13:23,446 because you will still be dealing with them in Objective-C 245 00:13:23,446 --> 00:13:28,156 and a lot of the iOS code will be dealing with some structs. 246 00:13:28,606 --> 00:13:30,836 Unfortunately, it can be somewhat confusing 'cause you 247 00:13:30,836 --> 00:13:33,626 might forget when you're dealing with a struct versus an object 248 00:13:33,626 --> 00:13:34,696 since they are different. 249 00:13:35,096 --> 00:13:38,536 But let's look an example of using a struct. 250 00:13:38,676 --> 00:13:42,926 Remember, struct is pure C and objects are Objective-C. 251 00:13:43,516 --> 00:13:45,516 [ Pause ] 252 00:13:46,016 --> 00:13:47,000 [ Inaudible Remark ] 253 00:13:47,836 --> 00:13:47,976 Yes. 254 00:13:48,516 --> 00:13:50,586 [ Inaudible Remark ] 255 00:13:51,086 --> 00:13:52,466 So you can. 256 00:13:52,986 --> 00:13:57,706 Once we get to Objective-C, you can, yes. 257 00:13:58,316 --> 00:14:02,426 It's-- A struct is literarily just a wrapper for a-- 258 00:14:02,996 --> 00:14:05,496 like a group of variables. 259 00:14:05,556 --> 00:14:07,946 So you're going to have a variable point 260 00:14:07,946 --> 00:14:10,116 to an object then you can store that variable 261 00:14:10,116 --> 00:14:13,686 in a struct just as well. 262 00:14:13,866 --> 00:14:16,506 Looking at a struct example that doesn't use objects. 263 00:14:17,516 --> 00:14:21,736 [ Pause ] 264 00:14:22,236 --> 00:14:26,626 We see here this typedef struct student. 265 00:14:27,516 --> 00:14:33,976 So the only reason for the typedef is so that-- 266 00:14:34,456 --> 00:14:35,806 [inaudible] technically it's a student here. 267 00:14:35,806 --> 00:14:37,376 But the only reason for the typedef is 268 00:14:37,376 --> 00:14:39,386 so that whenever we want to declare a variable 269 00:14:39,386 --> 00:14:43,376 of this struct type, if we just do this, now we have to say, 270 00:14:43,376 --> 00:14:45,656 struct student X and struct student Y. 271 00:14:46,076 --> 00:14:48,416 So the typedef just saves us that. 272 00:14:48,776 --> 00:14:52,256 And now I can just say struct student-- 273 00:14:52,256 --> 00:14:56,626 or now we can just say student X and student Y. 274 00:14:57,016 --> 00:14:58,556 So what is inside of this struct? 275 00:14:58,886 --> 00:15:01,086 We have an age and we have a name. 276 00:15:01,616 --> 00:15:04,586 And so, these are exactly what structs will look 277 00:15:04,586 --> 00:15:06,226 like in Objective-C. 278 00:15:06,706 --> 00:15:11,156 And coming down here, we see we declare a variable 279 00:15:11,156 --> 00:15:16,856 of this struct type, Alice, and we're going to use .notation 280 00:15:16,856 --> 00:15:18,846 to access the fields in that struck. 281 00:15:19,186 --> 00:15:23,396 So, Alice.age equals 20 and Alice.name equals Alice. 282 00:15:23,446 --> 00:15:25,346 And we could do the same thing, we just declare Bob 283 00:15:25,756 --> 00:15:30,526 and that's pretty much like everything 284 00:15:30,526 --> 00:15:32,136 about Structs that you will need. 285 00:15:32,646 --> 00:15:34,506 So, questions? 286 00:15:34,506 --> 00:15:39,046 Oh, and then if you want, look at degree [phonetic] function. 287 00:15:39,596 --> 00:15:43,886 Up here we are storing inside of Bob at age 21 288 00:15:44,186 --> 00:15:47,446 and down here we are accessing Bob.age. 289 00:15:50,886 --> 00:15:56,116 OK. Next, we will also have enums 290 00:15:56,586 --> 00:15:59,556 which are somewhat more important in Objective-C 291 00:15:59,556 --> 00:16:03,416 than they were in-- perhaps you've used in regular C 292 00:16:03,666 --> 00:16:08,996 since there's a lot of the-- a lot of code you'll be working 293 00:16:08,996 --> 00:16:10,486 with uses a lot of enums. 294 00:16:11,226 --> 00:16:12,926 So, what does an enum look like? 295 00:16:12,926 --> 00:16:16,596 So, it's like a struct and again we're just using typedef so that 296 00:16:16,596 --> 00:16:18,186 when we want to declare a variable 297 00:16:18,186 --> 00:16:22,046 of this enum type we don't have to say enum genders X 298 00:16:22,046 --> 00:16:24,736 and enum genders Y. Thanks to the typedef you're going 299 00:16:24,736 --> 00:16:28,226 to say genders X and genders Y. So, 300 00:16:29,356 --> 00:16:31,906 enums aren't strictly necessary. 301 00:16:32,226 --> 00:16:36,526 We could instead do hash define female as 0 302 00:16:36,846 --> 00:16:39,026 and hash define male as 1. 303 00:16:39,356 --> 00:16:42,586 And hash define just declares this to be a constant. 304 00:16:42,966 --> 00:16:46,736 So right now, if I got rid of this, 305 00:16:46,876 --> 00:16:50,586 the two programs will be almost equivalent except for the fact 306 00:16:50,586 --> 00:16:54,576 that I just got rid of the genders type. 307 00:16:54,676 --> 00:16:57,766 So, why do we prefer enums over these hash defines? 308 00:16:58,106 --> 00:17:01,886 Because if I add a whole bunch of hash defines something two, 309 00:17:01,886 --> 00:17:04,106 something three, something four and then I decided 310 00:17:04,106 --> 00:17:05,886 to like, reorder them. 311 00:17:05,886 --> 00:17:09,536 Then I would have to like change the numbers on all the rest 312 00:17:09,536 --> 00:17:14,416 of them and also it's just a convenient that I don't have 313 00:17:14,416 --> 00:17:16,436 to explicitly list the numbers on all these things. 314 00:17:17,636 --> 00:17:21,706 Once we get to Objective-C and I think more specifically Xcode, 315 00:17:21,886 --> 00:17:26,726 there's also some-- well, it's coming down here. 316 00:17:27,836 --> 00:17:30,106 We see that we have changed this struct to now not-- 317 00:17:30,646 --> 00:17:32,316 or now it takes a name and a gender. 318 00:17:32,876 --> 00:17:36,096 So, Alice is going to be-- is going to be given the name Alice 319 00:17:36,096 --> 00:17:37,806 and it's going to be given the gender female. 320 00:17:38,296 --> 00:17:41,926 So, it's important to remember in C and also Objective-C 321 00:17:42,176 --> 00:17:45,046 that there is no enforcement of the gender's type. 322 00:17:45,646 --> 00:17:48,056 So, I am just as easily able 323 00:17:48,056 --> 00:17:50,486 to put a hundred underneath the hood 324 00:17:50,486 --> 00:17:52,516 and enum is literally just an integer. 325 00:17:52,706 --> 00:17:57,446 So, even though a hundred is not a valid genders, 326 00:17:58,266 --> 00:18:00,006 it will let me do this. 327 00:18:01,006 --> 00:18:04,596 But in Xcode, generally it will-- 328 00:18:05,036 --> 00:18:08,696 it will yell at you like visually if you're using things 329 00:18:08,696 --> 00:18:10,146 that aren't correct enum types. 330 00:18:10,816 --> 00:18:13,656 So, you'll wan to use these enums correctly. 331 00:18:14,286 --> 00:18:19,196 And that's pretty much it for enums. 332 00:18:20,016 --> 00:18:20,476 Questions? 333 00:18:21,516 --> 00:18:24,276 [ Pause ] 334 00:18:24,776 --> 00:18:37,366 OK. So then, arrays, regular C arrays are still going 335 00:18:37,366 --> 00:18:39,356 to work in Objective-C. 336 00:18:39,356 --> 00:18:40,626 You're also going to see 337 00:18:40,626 --> 00:18:42,596 that there are these new array classes 338 00:18:42,596 --> 00:18:44,496 that you're probably going to want to get used to. 339 00:18:44,496 --> 00:18:46,816 So, you might not be using them that much. 340 00:18:47,606 --> 00:18:49,956 Just to look at an example of using the arrays. 341 00:18:50,516 --> 00:18:55,576 [ Pause ] 342 00:18:56,076 --> 00:19:00,866 So, here we declare the variable int 10. 343 00:19:01,066 --> 00:19:05,056 We print enter number of exams and then scanf is just a way 344 00:19:05,056 --> 00:19:07,376 of grabbing input from the keyboard. 345 00:19:07,906 --> 00:19:11,836 So here we are scanf'ing for some integer, 346 00:19:11,986 --> 00:19:14,366 this percent D carries over from printdef. 347 00:19:14,366 --> 00:19:15,656 It's looking for an integer. 348 00:19:16,166 --> 00:19:17,666 And why do we need to-- 349 00:19:17,666 --> 00:19:21,896 why do we need to pass ampersand N and not just N? 350 00:19:22,326 --> 00:19:23,876 Why would this never work? 351 00:19:24,516 --> 00:19:28,516 [ Pause ] 352 00:19:29,016 --> 00:19:30,000 [ Inaudible Remark ] 353 00:19:31,296 --> 00:19:34,646 Yeah. So inside of this scanf function, 354 00:19:34,646 --> 00:19:36,816 just like we saw before the swap function, 355 00:19:37,076 --> 00:19:42,006 ideally after this point in time N equals whatever number I type 356 00:19:42,006 --> 00:19:42,976 at the keyboard. 357 00:19:43,666 --> 00:19:50,916 So, scanf needs to actually change this N. Scanf can't 358 00:19:51,006 --> 00:19:54,096 change that without a pointer to that N, 359 00:19:54,096 --> 00:19:56,616 without having the address of that N. Otherwise, 360 00:19:56,616 --> 00:19:59,976 if I just did this and we'll first do in compile. 361 00:20:00,056 --> 00:20:03,366 But assuming it did accept that, it would just try 362 00:20:03,366 --> 00:20:09,066 to set the local variable N to the keyboard entered value 363 00:20:09,296 --> 00:20:11,866 and this N would remain unchanged. 364 00:20:12,306 --> 00:20:16,946 So, we need to pass the address. 365 00:20:17,086 --> 00:20:22,106 Here we are declaring an array and that array is going to be 366 00:20:22,106 --> 00:20:24,566 of size N. So we're going to have N integers. 367 00:20:25,026 --> 00:20:27,276 And this is all going on the stack so far. 368 00:20:28,456 --> 00:20:34,486 And then we're iterating over the N values entering a grade 369 00:20:34,486 --> 00:20:36,986 into each individual spot in the array. 370 00:20:37,456 --> 00:20:39,026 So really, this program is going to behave 371 00:20:39,026 --> 00:20:40,866 like how many grades you want to enter? 372 00:20:41,366 --> 00:20:43,646 Three. What is the first grade? 373 00:20:43,876 --> 00:20:44,806 What is the second grade? 374 00:20:44,936 --> 00:20:45,756 What is the third grade? 375 00:20:46,226 --> 00:20:47,496 So, you enter each grade. 376 00:20:48,456 --> 00:20:54,666 And also we have to-- So grades I is the Ith position 377 00:20:54,666 --> 00:20:58,566 in the array and then we also need to pass that by reference. 378 00:20:58,616 --> 00:21:01,936 We need to pass the pointer to grades I for the same reason 379 00:21:01,936 --> 00:21:03,476 that we needed to pass the pointer to N. 380 00:21:04,516 --> 00:21:06,936 [ Pause ] 381 00:21:07,436 --> 00:21:07,976 Questions? 382 00:21:08,516 --> 00:21:21,156 [ Pause ] 383 00:21:21,656 --> 00:21:23,896 OK. So, memory management. 384 00:21:24,606 --> 00:21:30,516 It's one of the bigger problems in C and for the most part, 385 00:21:30,516 --> 00:21:32,676 you are going to have to deal with it in Objective-C. 386 00:21:32,916 --> 00:21:35,416 There are some small things you'll have to think about 387 00:21:35,476 --> 00:21:37,006 and we'll get to that next week. 388 00:21:37,726 --> 00:21:42,626 But the malloc and free stuff that you're used to, 389 00:21:43,196 --> 00:21:44,606 you don't really have to deal with. 390 00:21:44,806 --> 00:21:50,206 So, remember that we have our stack and our heap. 391 00:21:50,726 --> 00:21:53,206 And so all of our local variables are always stored 392 00:21:53,206 --> 00:21:53,646 on the stack. 393 00:21:54,576 --> 00:21:59,176 And this means, let's say I call some function and it needs 394 00:21:59,176 --> 00:22:05,426 to like return some array to the function that called it. 395 00:22:05,926 --> 00:22:08,536 It can't just return-- it can't just return an array 396 00:22:08,536 --> 00:22:09,766 on the stack and return it, 397 00:22:09,846 --> 00:22:11,936 because once the function returns that array is gone. 398 00:22:12,106 --> 00:22:13,886 That's the point of it being a local variable. 399 00:22:13,886 --> 00:22:14,566 The array is gone. 400 00:22:15,076 --> 00:22:19,046 So, malloc, what that does, is allocate space on the heap 401 00:22:19,636 --> 00:22:21,506 and the stuff that out-- 402 00:22:21,506 --> 00:22:24,646 that's allocated on the heap survives past whenever the 403 00:22:24,646 --> 00:22:25,916 function happens to end, 404 00:22:26,176 --> 00:22:28,156 whenever that variable happens to go out of scope. 405 00:22:28,656 --> 00:22:33,716 And so what malloc and free are like manual memory management 406 00:22:33,716 --> 00:22:36,576 versus the automatic memory management of local variables. 407 00:22:37,276 --> 00:22:39,476 And something to keep in mind is 408 00:22:39,476 --> 00:22:42,516 that pretty much all objects are going to be like this. 409 00:22:42,616 --> 00:22:45,226 All objects are going to pretty much be malloc. 410 00:22:45,226 --> 00:22:46,276 They're going to go on the heap. 411 00:22:46,706 --> 00:22:51,286 And so they are going to continue existing 412 00:22:51,336 --> 00:22:54,476 after the scope of that variable ends. 413 00:22:55,496 --> 00:23:00,166 But thanks to the new iOS Objective-C features, 414 00:23:00,166 --> 00:23:03,076 you don't really have to think about freeing that memory. 415 00:23:03,366 --> 00:23:05,476 So we'll see why that's really useful. 416 00:23:06,516 --> 00:23:09,146 [ Inaudible Remark ] 417 00:23:09,646 --> 00:23:12,486 Yes. So, the new-- it's ARC, 418 00:23:12,486 --> 00:23:14,546 A-R-C is Automatic Reference Counting 419 00:23:14,926 --> 00:23:17,896 and it will automatically collect these objects for you. 420 00:23:18,306 --> 00:23:20,856 That was not the case two or three years ago. 421 00:23:20,856 --> 00:23:20,966 Yeah? 422 00:23:21,516 --> 00:23:25,136 [ Inaudible Remark ] 423 00:23:25,636 --> 00:23:28,056 When you don't want to use ARC? 424 00:23:28,056 --> 00:23:30,906 So, the only thing I could really think of is 425 00:23:30,906 --> 00:23:36,936 like if you wanted to be really explicit about the-- 426 00:23:37,076 --> 00:23:40,756 like you want to fine-tune your program, overly optimize it 427 00:23:40,756 --> 00:23:43,176 to make it like run better. 428 00:23:43,416 --> 00:23:49,266 But that's probably not the beast use of your time. 429 00:23:50,176 --> 00:23:54,066 It's-- You are already using Objective-C 430 00:23:54,066 --> 00:23:57,206 which there are a lot of things that that's not doing 431 00:23:57,206 --> 00:23:59,536 in the most optimized way possible. 432 00:23:59,876 --> 00:24:04,496 So, pretty much any app nowadays is going to use ARC. 433 00:24:05,516 --> 00:24:09,876 [ Inaudible Remark ] 434 00:24:10,376 --> 00:24:11,976 Oh, so an example-- 435 00:24:12,516 --> 00:24:16,766 [ Inaudible Remark ] 436 00:24:17,266 --> 00:24:18,876 It probably would. 437 00:24:19,676 --> 00:24:22,886 But it's not really worth even trying 438 00:24:22,886 --> 00:24:24,806 to optimize your app for that. 439 00:24:25,016 --> 00:24:26,146 [ Inaudible Remark ] 440 00:24:26,146 --> 00:24:26,346 Yeah. 441 00:24:27,516 --> 00:24:35,356 [ Inaudible Remark ] 442 00:24:35,856 --> 00:24:36,806 No, it will not. 443 00:24:36,806 --> 00:24:38,576 You pretty much shouldn't be malloc'ing. 444 00:24:39,146 --> 00:24:43,316 I actually wonder, I'm not a hundred percent sure, 445 00:24:43,316 --> 00:24:47,786 but I imagine it's already taking very strict control 446 00:24:47,786 --> 00:24:48,926 of what the heap looks like. 447 00:24:48,926 --> 00:24:50,846 And so, if you start malloc'ing things on top 448 00:24:50,846 --> 00:24:52,166 of what it's trying to do with the heap, 449 00:24:52,166 --> 00:24:54,156 it might screw it up but I'm not sure. 450 00:24:55,376 --> 00:25:00,686 You won't need to malloc. 451 00:25:00,686 --> 00:25:02,316 OK. Objective-C. 452 00:25:02,846 --> 00:25:05,396 So C questions before we move on to Objective-C stuff. 453 00:25:05,796 --> 00:25:05,916 Yeah. 454 00:25:06,336 --> 00:25:08,336 [ Inaudible Remark ] 455 00:25:08,656 --> 00:25:12,236 Oh. So that's-- Well, in C you would need to use free. 456 00:25:12,426 --> 00:25:16,356 So anything you malloc, at some point during the life 457 00:25:16,356 --> 00:25:17,876 of your program, you should also free. 458 00:25:18,966 --> 00:25:22,336 In Objective-C, that's the thing so things are going 459 00:25:22,336 --> 00:25:26,266 to be somewhat automatically allocated for you 460 00:25:26,516 --> 00:25:30,386 and they will be automatically de-allocated for you as long 461 00:25:30,386 --> 00:25:33,756 as you adhere to some things we'll see next week. 462 00:25:33,896 --> 00:25:40,816 OK. Any other questions about C before some Objective-C stuff? 463 00:25:40,976 --> 00:25:46,976 OK. So, from our Hello World in C to our Hello World 464 00:25:46,976 --> 00:25:51,256 in Objective-C, there aren't too many changes. 465 00:25:51,256 --> 00:25:54,706 You'll see that it looks a lot like C in a lot of ways. 466 00:25:55,626 --> 00:25:58,016 Unfortunately, the first word has literally changed. 467 00:25:58,166 --> 00:26:01,516 So what do you think the difference is between include-- 468 00:26:01,686 --> 00:26:03,956 like we used to say hash include, now we say hash import. 469 00:26:03,956 --> 00:26:05,536 So what do you think the difference is there? 470 00:26:06,516 --> 00:26:09,976 [ Pause ] 471 00:26:10,476 --> 00:26:14,916 So hash import is smarter than hash include 472 00:26:14,916 --> 00:26:17,976 and that it will only import something exactly once. 473 00:26:19,026 --> 00:26:22,946 And so, this used to be an issue with hash includes 474 00:26:22,946 --> 00:26:25,616 like if you hash include a header file twice 475 00:26:25,616 --> 00:26:28,556 and you don't take special precautions in that header file, 476 00:26:28,906 --> 00:26:30,696 then you might duplicate some definitions 477 00:26:30,696 --> 00:26:31,976 of things and it won't compile. 478 00:26:32,866 --> 00:26:34,636 Hash import, no matter how-- 479 00:26:34,636 --> 00:26:36,576 if I said hash import foundation dot-- 480 00:26:36,576 --> 00:26:38,876 or like if I just copy and paste this line, 481 00:26:39,106 --> 00:26:40,766 the second line wouldn't do anything. 482 00:26:41,776 --> 00:26:47,416 So, hash import just going to be more efficient in that. 483 00:26:47,636 --> 00:26:49,876 And the-- another thing 484 00:26:49,876 --> 00:26:53,996 that looks somewhat different is this @autoreleasepool. 485 00:26:54,406 --> 00:26:57,946 So that's going to be something we deal with next week. 486 00:26:57,946 --> 00:27:00,636 That has to do with automatic memory management. 487 00:27:02,676 --> 00:27:06,676 And the one thing to note and we'll also see it in front 488 00:27:06,676 --> 00:27:11,466 of the Hello World is @ is a very Objective-C thing. 489 00:27:11,466 --> 00:27:13,376 So like if you see code and you see an at symbol, 490 00:27:13,586 --> 00:27:15,976 you might be able to reason 491 00:27:15,976 --> 00:27:17,746 that it is Objective-C 'cause you're going 492 00:27:17,746 --> 00:27:19,286 to see this all over the place. 493 00:27:19,616 --> 00:27:23,696 In case of the Hello World, so normally we would see just 494 00:27:23,696 --> 00:27:27,226 like string hello world by putting the at symbol in front 495 00:27:27,226 --> 00:27:30,306 of it, we are making it an Objective-C type string. 496 00:27:30,716 --> 00:27:33,776 More explicitly we are making it an NS string. 497 00:27:34,066 --> 00:27:35,866 So we're going to see that in a couple of other places. 498 00:27:36,196 --> 00:27:41,716 But now this-- this at hello world is an object 499 00:27:41,846 --> 00:27:43,876 that we are passing to the NS log function. 500 00:27:44,566 --> 00:27:45,656 Let's actually run that. 501 00:27:46,516 --> 00:27:56,076 [ Pause ] 502 00:27:56,576 --> 00:27:59,196 So what is the ridiculous-- 503 00:28:00,076 --> 00:28:04,636 and so you will pretty much never need 504 00:28:04,636 --> 00:28:06,076 to compile at the command line. 505 00:28:06,076 --> 00:28:10,006 Because once we get into Xcode, that's going 506 00:28:10,006 --> 00:28:12,356 to pretty much be everything you need. 507 00:28:13,146 --> 00:28:16,066 But here, we have compiled that program. 508 00:28:16,066 --> 00:28:19,816 It's exactly the same as the one that we saw in the slide. 509 00:28:20,566 --> 00:28:25,096 And running it, we see something that looks like this. 510 00:28:26,806 --> 00:28:32,206 So, we see the date, we see the time, we see main 511 00:28:32,436 --> 00:28:34,706 and then this happens to be the process ID 512 00:28:34,706 --> 00:28:36,356 and then something called the "Mac Port" [phonetic] 513 00:28:36,356 --> 00:28:37,576 that you don't have to care about at all, 514 00:28:37,906 --> 00:28:39,996 and then the actual thing that we NSLogged. 515 00:28:40,666 --> 00:28:43,116 So, this is what NSLog does. 516 00:28:43,906 --> 00:28:47,876 You will probably be using NSLog pretty frequently 517 00:28:47,876 --> 00:28:50,656 in your programs to debug things. 518 00:28:51,046 --> 00:28:53,896 In actual released apps, you probably want to get rid 519 00:28:53,896 --> 00:28:56,116 of your NSLogs or have them wrapped in, like, 520 00:28:56,276 --> 00:28:57,596 debug type statements. 521 00:28:58,286 --> 00:28:59,936 Since-- Once you're on an iPhone, 522 00:28:59,936 --> 00:29:01,416 you pretty much don't have access 523 00:29:01,416 --> 00:29:02,686 to anything that is NSLogged. 524 00:29:03,416 --> 00:29:05,636 I think theoretically, you can like plug in your iPhones 525 00:29:05,636 --> 00:29:08,226 to your computer and see what was NSLogged. 526 00:29:09,356 --> 00:29:11,486 But that's rare. 527 00:29:11,486 --> 00:29:12,366 Like, anything released 528 00:29:12,366 --> 00:29:13,846 to the App Store isn't going to have any of those. 529 00:29:14,516 --> 00:29:22,576 [ Pause ] 530 00:29:23,076 --> 00:29:28,216 OK. So this is our first exposure to an object, 531 00:29:28,216 --> 00:29:28,906 but it doesn't really feel 532 00:29:28,906 --> 00:29:30,306 like an object 'cause we're pretty much putting 533 00:29:30,306 --> 00:29:31,286 that sign in front of it. 534 00:29:31,686 --> 00:29:35,836 That's technically shorthand for creating a string object. 535 00:29:36,356 --> 00:29:39,296 And we-- I think we'll see the longhand later 536 00:29:39,296 --> 00:29:41,126 or at least see many other objects 537 00:29:41,126 --> 00:29:42,566 that we're going to be creating. 538 00:29:43,276 --> 00:29:45,756 So, use those signs that just says everything 539 00:29:45,756 --> 00:29:46,916 so far has been the command line. 540 00:29:47,266 --> 00:29:49,336 Everything can be done at the command line. 541 00:29:49,936 --> 00:29:52,256 You probably won't want to do things at the command line. 542 00:29:52,846 --> 00:29:55,906 So, Xcode is pretty-- 543 00:29:57,486 --> 00:30:00,636 pretty comprehensive on all the things Objective-C in iOS. 544 00:30:02,446 --> 00:30:08,966 You should be able to get it for free and we aren't really going 545 00:30:08,966 --> 00:30:11,766 to go into the details of what all these different places 546 00:30:11,766 --> 00:30:12,616 in Xcode are. 547 00:30:12,616 --> 00:30:14,526 It's pretty overwhelming the first time you see it. 548 00:30:14,876 --> 00:30:17,056 The only things we're going to be using today, like-- 549 00:30:17,056 --> 00:30:19,516 it's going to look like three of them. 550 00:30:19,726 --> 00:30:21,486 So, we're not going to be using utility area. 551 00:30:22,026 --> 00:30:23,896 The debug area is where we're going to use to see 552 00:30:23,896 --> 00:30:25,976 where NSLog things are going to be printing. 553 00:30:26,136 --> 00:30:28,646 The editor area is where we're going to see our code. 554 00:30:28,996 --> 00:30:34,476 And navigator area, we're just going to see our files. 555 00:30:34,476 --> 00:30:37,206 And it also contains all this debuggings, important stuff, 556 00:30:37,206 --> 00:30:39,556 but we're not going to go into that. 557 00:30:39,736 --> 00:30:46,436 So, you could-- if you have an iOS device and you want 558 00:30:46,436 --> 00:30:48,506 to actually install these apps to your iOS device, 559 00:30:48,566 --> 00:30:49,936 this was discussed last week. 560 00:30:50,436 --> 00:30:52,546 But you need a developer account. 561 00:30:52,896 --> 00:30:55,406 So through us, you can get a free account. 562 00:30:55,796 --> 00:30:58,736 But you are not able to actually put the things on the App Store. 563 00:30:58,926 --> 00:31:01,846 So if you want to put things on the App Store, you will want 564 00:31:01,846 --> 00:31:05,936 to get your own accounts which is 99 dollars per yourself 565 00:31:05,936 --> 00:31:08,296 and I think like 2.99 for a company or something. 566 00:31:09,286 --> 00:31:13,626 So, you're going to look up a lot more there 567 00:31:14,176 --> 00:31:17,046 and this will be put online later. 568 00:31:18,206 --> 00:31:21,786 So, the new data types in Objective-C, 569 00:31:22,376 --> 00:31:26,536 there is pretty much only two big primitive data types 570 00:31:26,536 --> 00:31:29,936 that you need to care about, so BOOL and ID. 571 00:31:30,466 --> 00:31:33,776 So, a BOOL is like a BOOL in every other language. 572 00:31:34,226 --> 00:31:37,106 Unfortunately, it is not true and false. 573 00:31:37,166 --> 00:31:38,536 It is yes and no. 574 00:31:39,096 --> 00:31:40,576 So you're going to be seeing a lot of capital, 575 00:31:40,576 --> 00:31:42,706 yes's and capital no's as in your programs. 576 00:31:43,366 --> 00:31:46,376 I think the reason for that is once we started seeing 577 00:31:46,376 --> 00:31:50,206 functions, the way the functions are awarded, 578 00:31:50,206 --> 00:31:52,936 it's kind of like-- and do you want this? 579 00:31:53,286 --> 00:31:54,806 Yes. And do you want this? 580 00:31:54,806 --> 00:32:00,996 No. ID. So, if you're more familiar with C 581 00:32:00,996 --> 00:32:02,326 and you know what void star is, 582 00:32:02,326 --> 00:32:04,716 ID is sort of like that but for objects. 583 00:32:04,996 --> 00:32:08,826 ID just sort of represents like a generic object. 584 00:32:08,826 --> 00:32:11,026 You don't know what the type of the object is, but you know 585 00:32:11,026 --> 00:32:12,416 that this thing is an object. 586 00:32:13,236 --> 00:32:17,146 And nil is sort of the counter point-- counterpart of null. 587 00:32:17,426 --> 00:32:22,346 So nil represents a non-existing object 588 00:32:22,526 --> 00:32:23,886 but it has some special properties. 589 00:32:26,136 --> 00:32:26,816 Questions? 590 00:32:30,166 --> 00:32:34,206 OK. So here are some data types that if you saw 591 00:32:34,206 --> 00:32:36,676 when we hash imported foundation slash foundation dot H 592 00:32:37,006 --> 00:32:38,006 which pretty much everything you're going 593 00:32:38,006 --> 00:32:39,086 to be doing is going to do. 594 00:32:39,086 --> 00:32:42,616 We also get some of these data types and as integer 595 00:32:42,616 --> 00:32:44,846 and as point and as rect. 596 00:32:45,036 --> 00:32:49,856 These are not objects and this can be somewhat confusing 597 00:32:50,966 --> 00:32:53,266 because it can be somewhat difficult to differentiate 598 00:32:53,266 --> 00:32:56,506 between objects and just these typedef things. 599 00:32:56,946 --> 00:33:04,796 So, they exist for various, like, legacy reasons and so, 600 00:33:04,796 --> 00:33:08,826 like, NSInteger exist as sort of this weird bridge between 32 bit 601 00:33:08,826 --> 00:33:12,656 and 64 bit and pretty much use it whenever like-- 602 00:33:12,836 --> 00:33:14,476 when you're looking at documentation and you see 603 00:33:14,476 --> 00:33:16,756 that this function returns an NSInteger, 604 00:33:17,286 --> 00:33:18,816 use an NSInteger variable. 605 00:33:19,326 --> 00:33:24,616 So, none of these are object types. 606 00:33:25,866 --> 00:33:28,576 Now, just a quick discussion about what classes 607 00:33:28,576 --> 00:33:31,086 and objects are in case you don't have any 608 00:33:31,086 --> 00:33:32,796 object-oriented experience. 609 00:33:33,426 --> 00:33:36,776 So, we're going to be defining classes today. 610 00:33:37,286 --> 00:33:41,916 And a class in-- It's going to be similar in Objective-C 611 00:33:41,916 --> 00:33:43,216 to other languages you've seen. 612 00:33:43,406 --> 00:33:46,756 A class is going to define methods and variables 613 00:33:47,246 --> 00:33:50,756 and it's pretty much a blueprint that then objects, you're going 614 00:33:50,756 --> 00:33:52,236 to create from those classes. 615 00:33:52,716 --> 00:33:54,766 So a class is going to say like any object 616 00:33:54,766 --> 00:33:58,116 of this class should have these variables and these methods. 617 00:33:58,676 --> 00:34:02,546 And then it's on those objects that-- or in those objects, 618 00:34:02,546 --> 00:34:04,536 you're actually going to have those variables. 619 00:34:05,446 --> 00:34:10,066 So, you have a single class and many, many objects can come 620 00:34:10,106 --> 00:34:11,186 from that single class. 621 00:34:12,186 --> 00:34:13,946 It's also important to remember 622 00:34:13,946 --> 00:34:16,906 that in object-oriented programming, classes, 623 00:34:17,136 --> 00:34:19,326 you're going to have this hierarchical relationship 624 00:34:19,326 --> 00:34:20,576 that we're going to be seeing. 625 00:34:20,856 --> 00:34:22,776 So like if I define-- Well, 626 00:34:23,306 --> 00:34:25,736 in Java you might have seen like the objectClass. 627 00:34:26,046 --> 00:34:29,576 In Objective-C, the equivalent is NSObject. 628 00:34:30,096 --> 00:34:35,266 So, everything, almost everything in some way inherits 629 00:34:35,266 --> 00:34:37,056 from this NSObject class. 630 00:34:37,646 --> 00:34:44,736 And so-- so if I defined some class, person that inherits 631 00:34:44,736 --> 00:34:47,856 from NSObject, then I might define another class, 632 00:34:47,856 --> 00:34:50,166 student that inherits from a person 633 00:34:50,166 --> 00:34:52,696 and then I might define some other class, 634 00:34:52,816 --> 00:34:55,346 8th grader that inherits from student. 635 00:34:55,666 --> 00:34:58,316 So, remember that these classes have these 636 00:34:58,316 --> 00:34:59,686 hierarchical relationships. 637 00:35:00,316 --> 00:35:02,606 And this is important when you're looking 638 00:35:02,606 --> 00:35:05,316 through the documentation because if I look 639 00:35:05,316 --> 00:35:09,026 at some random-- like, if I look at the Apple documentation 640 00:35:09,026 --> 00:35:12,406 for the 8th grader class and it shows me, like, 641 00:35:13,016 --> 00:35:14,516 the method spelling homework. 642 00:35:14,916 --> 00:35:16,736 You might think that's the only method it has, 643 00:35:17,176 --> 00:35:18,646 but it has a lot more methods than that 644 00:35:18,646 --> 00:35:21,096 because it's also inherits all of the methods from all 645 00:35:21,096 --> 00:35:22,036 of his parent classes. 646 00:35:22,636 --> 00:35:25,256 So, you need to look through the hierarchy 647 00:35:25,256 --> 00:35:27,546 to know all the methods everything has. 648 00:35:29,236 --> 00:35:33,096 Question? OK. 649 00:35:33,656 --> 00:35:35,296 So, .h files. 650 00:35:37,136 --> 00:35:43,236 Unfortunately, the interface keyword is somewhat different 651 00:35:43,236 --> 00:35:46,066 from what you might think of as like a Java interface 652 00:35:46,406 --> 00:35:48,106 and some other languages interfaces. 653 00:35:48,806 --> 00:35:51,186 It's still similar and that you're going to be defining 654 00:35:51,546 --> 00:35:54,736 like you're just going to list the prototypes of the methods 655 00:35:54,736 --> 00:35:57,026 that you want to be in this class. 656 00:35:58,036 --> 00:36:02,546 But we'll see later this thing protocols and those are going 657 00:36:02,546 --> 00:36:04,206 to be more like the interfaces you're used 658 00:36:04,206 --> 00:36:05,116 to in other languages. 659 00:36:05,936 --> 00:36:11,696 So in .h files, we see-- we have this @interface, 660 00:36:12,136 --> 00:36:15,926 and so @ as usual telling us it's Objective-C. 661 00:36:16,276 --> 00:36:19,726 So @interface and this class is going to be called foo 662 00:36:19,896 --> 00:36:22,366 and then this colon indicates the class 663 00:36:22,436 --> 00:36:23,806 that we are inheriting from it. 664 00:36:24,036 --> 00:36:26,116 So our parent is going to be NSObject. 665 00:36:27,106 --> 00:36:30,846 And then this ugly syntax where we put curly braces 666 00:36:30,846 --> 00:36:33,116 and then instance variables go in the curly braces. 667 00:36:33,966 --> 00:36:36,076 And then underneath the curly braces, 668 00:36:36,076 --> 00:36:39,276 we declare all the methods that this class needs to define. 669 00:36:39,816 --> 00:36:43,146 And we'll see plenty examples of those. 670 00:36:43,696 --> 00:36:45,636 And then getting into .m files. 671 00:36:46,056 --> 00:36:48,796 So pretty much every .m files is going 672 00:36:48,796 --> 00:36:50,696 to have its corresponding .h file. 673 00:36:50,966 --> 00:36:53,656 Inside of the .m file, we give the implementation 674 00:36:53,966 --> 00:36:55,016 of these things. 675 00:36:55,016 --> 00:36:57,716 And so here we're going to give the implementation of foo 676 00:36:57,866 --> 00:36:59,456 and actually define all the methods 677 00:36:59,456 --> 00:37:01,756 that in this .h file we said we would define. 678 00:37:05,516 --> 00:37:07,866 OK. So we'll look at an example. 679 00:37:08,326 --> 00:37:13,006 And this time we'll do it in the next code. 680 00:37:13,116 --> 00:37:13,726 Actually. 681 00:37:14,516 --> 00:37:24,816 [ Pause ] 682 00:37:25,316 --> 00:37:25,836 All right. 683 00:37:26,636 --> 00:37:31,526 So, here we see on this left side, we have our files. 684 00:37:31,856 --> 00:37:33,606 I'm going to get rid of this right side 'cause we don't need 685 00:37:33,606 --> 00:37:33,996 it now. 686 00:37:34,376 --> 00:37:36,176 Up in the-- or down at the bottom, 687 00:37:36,296 --> 00:37:38,816 we're going to have our NSLogs stuff down here. 688 00:37:39,526 --> 00:37:41,276 So looking through these files-- 689 00:37:41,556 --> 00:37:44,596 I'm not going to be able to do that. 690 00:37:45,076 --> 00:37:50,986 So looking to these files and we see-- we have a main function. 691 00:37:51,196 --> 00:37:53,056 We have the same AutoReleasePool thing 692 00:37:53,056 --> 00:37:54,356 that you can ignore for now. 693 00:37:54,856 --> 00:37:57,646 And then we're going to have these student star Alice. 694 00:37:58,076 --> 00:38:03,256 So, student we see over here is going to be an object. 695 00:38:03,256 --> 00:38:05,226 We have .h file and .m file for it. 696 00:38:06,676 --> 00:38:09,416 We'll look at those in a second. 697 00:38:09,416 --> 00:38:14,856 Student star, so I guess I'll go into that. 698 00:38:16,096 --> 00:38:17,616 Ignore this for a second. 699 00:38:18,296 --> 00:38:20,316 So, just student star Alice, 700 00:38:20,656 --> 00:38:22,016 we're going to allocate the student. 701 00:38:22,176 --> 00:38:23,716 So this is sort of like malloc. 702 00:38:24,026 --> 00:38:26,706 So, we're making broom for the student. 703 00:38:27,386 --> 00:38:30,716 And then apparently, we have some age field 704 00:38:30,716 --> 00:38:31,736 and some name field. 705 00:38:31,736 --> 00:38:33,066 Let's actually look at it. 706 00:38:33,066 --> 00:38:36,086 So here's student.h. And we have interface student, 707 00:38:36,086 --> 00:38:37,896 it's inheriting from NSObject. 708 00:38:38,756 --> 00:38:41,336 And here we see this @public keyword. 709 00:38:41,716 --> 00:38:44,296 This tells us that everything underneath that-- 710 00:38:44,366 --> 00:38:46,376 all the variables underneath this word are going 711 00:38:46,376 --> 00:38:48,006 to be public instance variables. 712 00:38:48,536 --> 00:38:51,016 There's also app protected and app private. 713 00:38:51,236 --> 00:38:53,536 So private, no other class is going to be able 714 00:38:53,536 --> 00:38:57,466 to see these variables and protected any class 715 00:38:57,516 --> 00:38:59,896 that is a subclass of this class is going to be able 716 00:38:59,896 --> 00:39:01,076 to access these variables. 717 00:39:01,906 --> 00:39:04,606 So you won't need to deal with those too much. 718 00:39:05,536 --> 00:39:08,076 Generally, you want to make the access 719 00:39:08,076 --> 00:39:10,206 to these variables as tight as possible. 720 00:39:10,306 --> 00:39:13,546 So like if the variables can be private, make them private. 721 00:39:14,476 --> 00:39:19,286 So here, the instance variables we have are age and name 722 00:39:19,286 --> 00:39:20,986 which is an NSStrings star. 723 00:39:21,516 --> 00:39:25,966 And we see since there are no methods defined down here, 724 00:39:26,136 --> 00:39:27,926 that means that, well, 725 00:39:27,926 --> 00:39:32,836 let's look at it student.m doesn't need define any methods. 726 00:39:34,136 --> 00:39:34,456 Yes? 727 00:39:35,516 --> 00:39:38,776 [ Inaudible Remark ] 728 00:39:39,276 --> 00:39:40,926 Why do we use what? 729 00:39:41,516 --> 00:39:44,636 [ Inaudible Remark ] 730 00:39:45,136 --> 00:39:50,456 Oh, so, we could use string or just char star 731 00:39:50,456 --> 00:39:54,796 like a regular C type string, but in Objective-C, you're going 732 00:39:54,796 --> 00:39:57,626 to be passing around these NSStrings a lot. 733 00:39:57,626 --> 00:39:59,976 So you're probably going to want this thing to be an NSString. 734 00:40:00,096 --> 00:40:02,406 Like when we want to actually print this, 735 00:40:02,546 --> 00:40:04,246 we're going to need print an NSString. 736 00:40:04,246 --> 00:40:06,796 We can't-- Oh, when we want to NSLog something, 737 00:40:06,796 --> 00:40:08,266 we need to NSLog objects. 738 00:40:08,666 --> 00:40:11,076 So we're going to need to pass it in NSString. 739 00:40:11,076 --> 00:40:13,256 We can't pass it a char star. 740 00:40:13,326 --> 00:40:15,916 We would have to change that char star to an NSString. 741 00:40:16,046 --> 00:40:18,566 >> But we also got NSInteger [inaudible]. 742 00:40:18,566 --> 00:40:23,466 >> Yeah. So, NSInteger is-- this is where it's-- 743 00:40:23,856 --> 00:40:29,446 NSInteger is pretty much going to be just a typedef 744 00:40:29,496 --> 00:40:32,266 for regular int or possible long. 745 00:40:32,506 --> 00:40:35,276 This is not an object type. 746 00:40:35,786 --> 00:40:36,826 This is not a class. 747 00:40:37,056 --> 00:40:42,396 This is just like typedef, NSInteger, int. 748 00:40:45,736 --> 00:40:51,556 So, this why like-- these aren't that helpful unless you see 749 00:40:51,556 --> 00:40:52,256 that a function 750 00:40:52,256 --> 00:40:54,726 in the documentation is returning an NSInteger. 751 00:40:55,006 --> 00:40:56,976 And then you should use NSIntegers. 752 00:40:57,516 --> 00:41:04,436 [ Inaudible Remark ] 753 00:41:04,936 --> 00:41:08,046 Yes. So that's the unfortunate thing. 754 00:41:08,396 --> 00:41:14,516 You got pretty-- like the primitive ones are these NS-- 755 00:41:14,516 --> 00:41:16,616 well, actually no, I can even say that. 756 00:41:16,616 --> 00:41:18,546 There are some complicated ones that are primitive 757 00:41:18,546 --> 00:41:21,426 and I wish they had done something 758 00:41:21,426 --> 00:41:23,666 to differentiate better, but they didn't. 759 00:41:23,666 --> 00:41:29,716 and let's change back to NS, but it shouldn't change anything. 760 00:41:30,846 --> 00:41:35,616 So, it mean-- So we are now accessing this. 761 00:41:35,836 --> 00:41:37,756 So student star Alice is an object. 762 00:41:38,076 --> 00:41:41,426 That object has an age field and a name field 763 00:41:41,716 --> 00:41:44,876 and we are accessing those and setting the age field to 20 764 00:41:44,876 --> 00:41:51,216 and we're setting the name field to be this NSString Alice. 765 00:41:51,726 --> 00:41:55,806 Note that this would not succeed without the @ 766 00:41:55,806 --> 00:41:57,496 because now it's not an NSString 767 00:41:57,496 --> 00:41:58,876 and it yells at us appropriately. 768 00:42:01,276 --> 00:42:08,546 And in case you're curious, this arrow syntax, it comes more 769 00:42:08,546 --> 00:42:12,156 from C, come-- the next example that I gave you, 770 00:42:12,156 --> 00:42:14,316 you will not be using this arrow syntax. 771 00:42:14,846 --> 00:42:19,006 But what it is, is-- so, 772 00:42:19,386 --> 00:42:22,106 we're treating Alice sort of as like a struct. 773 00:42:22,816 --> 00:42:25,386 And so, we are de-referencing that struct 774 00:42:26,026 --> 00:42:30,756 and then accessing the age field inside of that struck. 775 00:42:31,346 --> 00:42:36,506 So, arrow is equivalent to star Alice dot. 776 00:42:37,076 --> 00:42:40,856 It's-- This to just say very disgusting syntax since, 777 00:42:40,856 --> 00:42:41,846 that's why they give us arrow. 778 00:42:42,316 --> 00:42:47,796 Arrow just means, here is a pointer to a struct/object 779 00:42:48,546 --> 00:42:52,836 and go to that object and change this field at that object. 780 00:42:57,736 --> 00:43:02,186 But you will not be using arrows on objects ever. 781 00:43:02,626 --> 00:43:05,146 So, this is a pretty bad example, 782 00:43:05,216 --> 00:43:06,496 but this is our intro example. 783 00:43:08,116 --> 00:43:09,706 Do the same thing with Bob, we allocate 784 00:43:09,706 --> 00:43:11,876 and we give him an age, we give him a name. 785 00:43:12,166 --> 00:43:14,486 And then greet [phonetic] down here. 786 00:43:14,656 --> 00:43:21,726 We're going to NSLog and we see NSLog and we need to pass NSLog 787 00:43:21,726 --> 00:43:23,796 and NSString as its first argument. 788 00:43:24,146 --> 00:43:29,306 And so we see our normal percent D over here and as age is just 789 00:43:29,306 --> 00:43:32,936 as we saw in the student.h file, as age is just an int. 790 00:43:33,406 --> 00:43:34,346 And so that's fine. 791 00:43:34,936 --> 00:43:38,876 And as name was an NSString. 792 00:43:39,286 --> 00:43:43,286 And so, the NSLog version of like percent S 793 00:43:43,516 --> 00:43:48,796 for NSStrings is going to be this percent @. So, 794 00:43:48,796 --> 00:43:52,286 that is the flag for printing NSStrings. 795 00:43:54,136 --> 00:43:57,916 Actually running this, on top, hitting build or run. 796 00:43:58,046 --> 00:43:59,846 I forgot the shortcut for it. 797 00:43:59,846 --> 00:44:03,106 And down here we see the NSLog output. 798 00:44:03,266 --> 00:44:04,476 Hello Alice, you're 20. 799 00:44:04,636 --> 00:44:05,886 Hi Bob, you're 21. 800 00:44:09,316 --> 00:44:12,936 Questions on this simple example because it's going 801 00:44:12,936 --> 00:44:14,716 to be changing pretty substantially 802 00:44:14,716 --> 00:44:15,736 in the next example? 803 00:44:18,326 --> 00:44:20,326 [ Inaudible Remark ] 804 00:44:20,636 --> 00:44:24,976 Yeah. So, this is also what I kind of pause 805 00:44:24,976 --> 00:44:26,666 at before 'cause I don't want to say quite yet. 806 00:44:27,306 --> 00:44:30,576 Student star, student is really like-- 807 00:44:30,576 --> 00:44:36,066 Alice is the object but like pretty much read student star-- 808 00:44:36,066 --> 00:44:38,216 don't read that as a pointer to a student, 809 00:44:38,446 --> 00:44:42,176 just take student star to be like the type of the object. 810 00:44:42,586 --> 00:44:47,036 So, you will never really be dealing with a student Alice. 811 00:44:47,796 --> 00:44:50,416 You will always be dealing with a student star Alice. 812 00:44:54,216 --> 00:45:00,976 And in the next sample, going to students to-- 813 00:45:01,516 --> 00:45:06,516 [ Pause ] 814 00:45:07,016 --> 00:45:15,000 [ Inaudible Remark ] 815 00:45:15,896 --> 00:45:16,886 No, not really. 816 00:45:17,516 --> 00:45:21,736 [ Pause ] 817 00:45:22,236 --> 00:45:25,866 OK. So, in this example, let's look at .h first. 818 00:45:27,736 --> 00:45:33,026 So now, this is the same, it's inheriting from NSObject. 819 00:45:33,456 --> 00:45:35,196 We have changed this. 820 00:45:35,526 --> 00:45:38,106 We're no longer saying int age and NSString name. 821 00:45:38,176 --> 00:45:40,826 We're saying underscore age and underscore name. 822 00:45:41,106 --> 00:45:45,146 And that is a convention that in the past it used just 823 00:45:45,146 --> 00:45:46,876 to be a convention and now it's a convention 824 00:45:46,876 --> 00:45:48,056 that actually mean something. 825 00:45:48,056 --> 00:45:48,976 So you're going to want 826 00:45:48,976 --> 00:45:51,066 to pretty much always have these instance variables 827 00:45:51,066 --> 00:45:52,006 be underscored. 828 00:45:52,756 --> 00:45:55,166 And now, here we're getting 829 00:45:55,166 --> 00:45:58,526 to these strange looking method things. 830 00:45:58,526 --> 00:46:00,976 So, let's actually go back to slides for a second. 831 00:46:01,516 --> 00:46:03,516 [ Pause ] 832 00:46:04,016 --> 00:46:06,000 [ Inaudible Remark ] 833 00:46:06,616 --> 00:46:11,236 We'll see in a second why we want the underscores 834 00:46:12,226 --> 00:46:13,546 and I quite gotten there yet. 835 00:46:14,666 --> 00:46:16,246 OK. So instance variables, we saw, 836 00:46:16,246 --> 00:46:18,386 we know them @protected, @private, @public. 837 00:46:18,846 --> 00:46:20,216 And it's somewhat messy. 838 00:46:20,216 --> 00:46:21,816 But like when I said @public, 839 00:46:21,816 --> 00:46:23,876 everything beneath the @public would be public. 840 00:46:24,196 --> 00:46:26,946 But then if I switch to-- like if I @public int X 841 00:46:27,056 --> 00:46:30,226 and @private int Y. Y would be private 'cause it's underneath 842 00:46:30,566 --> 00:46:31,706 the private. 843 00:46:32,586 --> 00:46:35,926 OK. So, first let's look at this. 844 00:46:36,446 --> 00:46:38,536 So, messages. 845 00:46:39,156 --> 00:46:41,436 In other object-orientated languages, 846 00:46:41,436 --> 00:46:43,496 you don't really-- well, some you do. 847 00:46:43,646 --> 00:46:44,856 But Java, you don't. 848 00:46:45,656 --> 00:46:49,256 So, messages are going to be the way that we invoke methods 849 00:46:49,346 --> 00:46:51,366 on objects and classes. 850 00:46:52,076 --> 00:46:55,726 So here, this square bracket syntax is what you're going 851 00:46:55,726 --> 00:46:57,206 to be using to send messages. 852 00:46:57,206 --> 00:46:58,856 And here we're saying, 853 00:46:59,266 --> 00:47:03,026 the student class has a method called "alloc." 854 00:47:03,596 --> 00:47:07,476 And so, send to the student class that method. 855 00:47:08,016 --> 00:47:09,306 Invoke that method. 856 00:47:09,856 --> 00:47:12,886 And then that is supposed to return a student star. 857 00:47:13,816 --> 00:47:19,706 And so this alloc is going to be pretty much everywhere. 858 00:47:19,866 --> 00:47:22,816 You-- Whenever you need to allocate an object, 859 00:47:22,816 --> 00:47:24,256 you need to do some sort of alloc. 860 00:47:24,876 --> 00:47:27,666 Sometimes, there is like alloc, 861 00:47:29,456 --> 00:47:32,106 sometimes there are some other alloc type function you might be 862 00:47:32,106 --> 00:47:34,126 using, but you're almost always going 863 00:47:34,126 --> 00:47:35,686 to be alloc'ing these things. 864 00:47:36,716 --> 00:47:41,436 So, here-- So there are two different types of methods 865 00:47:41,546 --> 00:47:43,676 like there are in other object-oriented languages. 866 00:47:44,036 --> 00:47:46,526 So we have instance methods and class methods. 867 00:47:47,156 --> 00:47:48,596 And so, the way we're going to differentiate 868 00:47:48,596 --> 00:47:51,306 between those is all the way on the left side, 869 00:47:51,306 --> 00:47:52,626 you see we have this minus sign. 870 00:47:53,646 --> 00:47:56,906 So, if we have a minus sign that means the method is going 871 00:47:56,906 --> 00:47:58,046 to be an instance method. 872 00:47:58,046 --> 00:48:00,326 And if we have a plus sign that means 873 00:48:00,326 --> 00:48:02,126 that it's going to be a class method. 874 00:48:02,746 --> 00:48:04,516 And an instance method is something 875 00:48:04,516 --> 00:48:07,516 that you actually need an object to use the method 876 00:48:07,836 --> 00:48:09,036 and a class method is something 877 00:48:09,036 --> 00:48:10,946 where you don't need an object to use the method. 878 00:48:11,096 --> 00:48:14,136 So going back to here, the fact that we're calling alloc 879 00:48:14,136 --> 00:48:18,076 on the student class tells us that alloc is a class method 880 00:48:18,576 --> 00:48:23,076 because we don't actually need a student to allocate a student. 881 00:48:23,436 --> 00:48:25,906 That'd be pretty flawed if we couldn't actually get a student 882 00:48:25,906 --> 00:48:27,876 without having a student. 883 00:48:28,516 --> 00:48:30,796 [ Inaudible Remark ] 884 00:48:31,296 --> 00:48:32,416 Yes. So, yeah. 885 00:48:32,656 --> 00:48:36,336 The static keyword from Java is the equivalent of plus. 886 00:48:36,856 --> 00:48:44,116 So the syntax for these things, we see all the way 887 00:48:44,196 --> 00:48:47,926 in the left is going to go plus or minus always. 888 00:48:47,926 --> 00:48:51,006 And then we're going to have the return type of the method. 889 00:48:51,296 --> 00:48:54,146 So here we have void, int, void. 890 00:48:54,946 --> 00:48:58,066 Then after return type, we have the name of the method. 891 00:48:58,616 --> 00:49:03,536 And so we have the name init and we the name age. 892 00:49:03,866 --> 00:49:05,186 And then technically the name 893 00:49:05,186 --> 00:49:08,816 of the last method is going to be set age colon. 894 00:49:09,816 --> 00:49:11,516 We'll see why. 895 00:49:11,936 --> 00:49:18,196 But this here-- this age is what we're just going 896 00:49:18,196 --> 00:49:19,676 to call that variable. 897 00:49:19,896 --> 00:49:21,506 And this is the type of that variable. 898 00:49:22,066 --> 00:49:25,106 So, this method isn't going to return anything. 899 00:49:25,456 --> 00:49:28,486 It's called set age colon and we would pass it some integer. 900 00:49:29,516 --> 00:49:33,436 [ Pause ] 901 00:49:33,936 --> 00:49:38,236 So, sending those messages, we see that student-- 902 00:49:38,236 --> 00:49:41,316 we're using lowercase student, so the student over here, 903 00:49:41,316 --> 00:49:44,166 the student object, since these are instance methods, 904 00:49:44,166 --> 00:49:46,736 we need to send these messages to objects. 905 00:49:47,866 --> 00:49:50,576 So we send the init message to student. 906 00:49:51,006 --> 00:49:52,896 We send the age message to student. 907 00:49:52,896 --> 00:49:54,466 And then we sent set age 908 00:49:54,746 --> 00:49:58,116 with the parameter 20, with the argument 20. 909 00:49:59,596 --> 00:50:00,406 Questions? 910 00:50:02,516 --> 00:50:13,176 [ Inaudible Remark ] 911 00:50:13,676 --> 00:50:14,706 What do you mean? 912 00:50:15,516 --> 00:50:21,236 [ Inaudible Remark ] 913 00:50:21,736 --> 00:50:24,856 >> Yes. That is how you should call it. 914 00:50:25,516 --> 00:50:28,196 [ Inaudible Remark ] 915 00:50:28,696 --> 00:50:29,726 Could you call as what? 916 00:50:29,726 --> 00:50:33,326 >> Like I would in C. 917 00:50:33,576 --> 00:50:35,116 >> How would you call it in C? 918 00:50:35,116 --> 00:50:41,826 >> I mean is that like I would say C and then like that? 919 00:50:41,826 --> 00:50:42,336 >> Oh err-- so no. 920 00:50:42,886 --> 00:50:45,876 This is why the previous example is something that was bad. 921 00:50:45,876 --> 00:50:49,566 You should very barely be differencing objects. 922 00:50:49,856 --> 00:50:52,106 I almost want to say never difference objects. 923 00:50:52,106 --> 00:50:55,566 And so, the arrow operator is n implicit difference. 924 00:50:56,036 --> 00:50:58,396 And so init is also somewhat different 925 00:50:58,396 --> 00:51:00,926 from setting the fields of the object. 926 00:51:01,486 --> 00:51:04,836 And another reason why the previous example was bad, 927 00:51:05,516 --> 00:51:09,006 you always-- you never want to deal with an object 928 00:51:09,006 --> 00:51:11,016 that was allocated but not initialized. 929 00:51:11,496 --> 00:51:15,826 So, even though the student objects, and we'll see 930 00:51:15,826 --> 00:51:17,076 in the next example how-- 931 00:51:17,176 --> 00:51:19,346 how originally just had like student alloc 932 00:51:19,456 --> 00:51:21,156 and I did Alice arrow age. 933 00:51:21,876 --> 00:51:23,106 I shouldn't have done that. 934 00:51:23,106 --> 00:51:25,976 I should have done student alloc init. 935 00:51:26,716 --> 00:51:28,606 So always initialize your objects 936 00:51:29,036 --> 00:51:30,736 and then I could access those fields. 937 00:51:31,436 --> 00:51:32,436 But then on top of that, 938 00:51:32,436 --> 00:51:34,426 I shouldn't be accessing those fields using arrows, 939 00:51:34,426 --> 00:51:35,496 I should be sending messages. 940 00:51:36,086 --> 00:51:39,296 And so we'll see that in the next example, 941 00:51:39,296 --> 00:51:40,746 the right way of doing that. 942 00:51:40,746 --> 00:51:43,726 And then we'll see that there are like 10 new 943 00:51:43,726 --> 00:51:45,826 or right ways of doing it. 944 00:51:48,256 --> 00:51:54,956 So selectors-- pretty much an alternative name for method, 945 00:51:55,196 --> 00:51:57,676 so alloc, init age and setAge colon. 946 00:51:57,676 --> 00:51:59,366 Remember the colon is part of the name? 947 00:51:59,686 --> 00:52:02,006 Once we see multiple argument functions, 948 00:52:02,006 --> 00:52:04,566 we'll see that there will be multiple callings in the name. 949 00:52:05,556 --> 00:52:08,396 So, all of those are just selectors 950 00:52:08,396 --> 00:52:10,206 and we'll see why that's relevant later. 951 00:52:11,176 --> 00:52:15,636 And let's look at that example now. 952 00:52:18,116 --> 00:52:20,166 So student two, OK. 953 00:52:20,806 --> 00:52:24,626 So, here we have said int underscore age 954 00:52:25,606 --> 00:52:27,126 and underscore name. 955 00:52:27,646 --> 00:52:32,756 And now we have for methods and this is like the getters 956 00:52:32,756 --> 00:52:34,946 and setters of Java that you might be used to. 957 00:52:34,946 --> 00:52:40,416 We have two methods, one called age and another called setAge 958 00:52:42,006 --> 00:52:45,526 that the first one is going to get the age of the thing. 959 00:52:45,776 --> 00:52:48,376 And the second one we're going to use to set the age. 960 00:52:48,506 --> 00:52:51,376 And then similarly down here, we have name and setName, 961 00:52:51,376 --> 00:52:53,566 the first we're going to use to retrieve the name 962 00:52:53,816 --> 00:52:56,276 and the second we're going to use to set the name. 963 00:52:56,766 --> 00:53:01,196 And these are important names both by convention 964 00:53:01,196 --> 00:53:03,006 and we'll see things that help us later 965 00:53:03,276 --> 00:53:04,956 where in other languages you might say 966 00:53:04,956 --> 00:53:06,296 like getName and setName. 967 00:53:06,546 --> 00:53:08,766 Here, the convention is just to say name. 968 00:53:08,956 --> 00:53:10,046 Do not say getName. 969 00:53:11,916 --> 00:53:12,416 Questions? 970 00:53:12,546 --> 00:53:19,536 OK, so looking at the implementation, 971 00:53:19,696 --> 00:53:21,566 we must be implementing these for methods. 972 00:53:22,566 --> 00:53:26,976 And so, notice, they are all instance methods, 973 00:53:26,976 --> 00:53:27,816 they are all minus. 974 00:53:28,776 --> 00:53:32,226 And age, we'll just going to return underscore age. 975 00:53:33,096 --> 00:53:36,346 And setAge, we're going to set underscore age. 976 00:53:37,166 --> 00:53:39,346 So we're going to set our instance variable age 977 00:53:39,616 --> 00:53:41,526 to the pass in argument age. 978 00:53:42,336 --> 00:53:44,806 We're going to return underscore name and we're going to set, 979 00:53:44,806 --> 00:53:46,976 and this one is somewhat interesting. 980 00:53:47,236 --> 00:53:50,046 So, we're going to set our instance variable underscore 981 00:53:50,046 --> 00:53:53,106 name to name copy. 982 00:53:53,946 --> 00:53:57,106 So, we know that this in fact is how we're going 983 00:53:57,106 --> 00:53:58,686 to send message to objects. 984 00:53:59,666 --> 00:54:02,276 Name is in NSString object. 985 00:54:03,156 --> 00:54:05,876 And so, apparently and you can look it up-- 986 00:54:05,916 --> 00:54:08,536 you can look in the documentation to verify this. 987 00:54:08,986 --> 00:54:14,746 Apparently name or NSString has an instance method called Copy 988 00:54:15,486 --> 00:54:18,826 that is going to return a copy of this NSString. 989 00:54:19,566 --> 00:54:22,216 And why do you think we want a copy of the NSString instead 990 00:54:22,216 --> 00:54:26,756 of just saying underscore name equals name? 991 00:54:27,516 --> 00:54:34,616 [ Pause ] 992 00:54:35,116 --> 00:54:35,216 Yeah. 993 00:54:35,396 --> 00:54:42,066 >> Well because it's an object, 994 00:54:42,316 --> 00:54:47,566 it should be modifying the pointers of that object 995 00:54:47,566 --> 00:54:49,586 so it would be modifying the initial objects. 996 00:54:49,626 --> 00:54:51,486 >> Yeah, so it isn't-- well actually, so, 997 00:54:51,486 --> 00:54:53,156 if we did not make a copy of the name, it isn't a thread 998 00:54:53,156 --> 00:54:54,566 that we are going to modify that NSString 999 00:54:54,796 --> 00:54:57,496 since we don't have any methods for modifying that NSString. 1000 00:54:57,496 --> 00:55:01,436 I guess we-- if we went around the proper method protocol, 1001 00:55:01,436 --> 00:55:03,066 we would be doing things. 1002 00:55:03,066 --> 00:55:06,726 We'll see why we should never be modifying name. 1003 00:55:07,396 --> 00:55:11,136 But it's possible that the NSString that was passed 1004 00:55:11,136 --> 00:55:14,186 to us @Bob or something is that-- 1005 00:55:14,486 --> 00:55:15,866 that could later be changed. 1006 00:55:16,186 --> 00:55:20,386 And so if that is changed then if we just do this, 1007 00:55:21,906 --> 00:55:23,006 then we are also going to-- 1008 00:55:23,006 --> 00:55:25,306 the name within this object will have been changed. 1009 00:55:25,476 --> 00:55:27,916 So we want to copy Bob for ourselves in case 1010 00:55:27,916 --> 00:55:29,976 if Bob has ever changed, we don't want to be changed. 1011 00:55:30,516 --> 00:55:33,586 [ Pause ] 1012 00:55:34,086 --> 00:55:37,456 OK, so looking at main.m [phonetic], 1013 00:55:38,166 --> 00:55:40,726 now this is the better way of doing this. 1014 00:55:41,006 --> 00:55:43,456 This is like appropriate objective-C. 1015 00:55:43,616 --> 00:55:46,216 We can see that there are more and more better ways but this is 1016 00:55:46,216 --> 00:55:49,766 at least like not bad. 1017 00:55:49,766 --> 00:55:53,376 So, we are appropriately initting and notice 1018 00:55:53,376 --> 00:55:56,396 that we are allowed to like nests these things. 1019 00:55:56,946 --> 00:56:05,506 So, we could if we wanted do student alloc 1020 00:56:05,766 --> 00:56:09,916 and then Alice equals Alice init, 1021 00:56:11,536 --> 00:56:14,876 but we are allowed to nests these calls. 1022 00:56:18,556 --> 00:56:22,476 OK and now we are, instead 1023 00:56:22,476 --> 00:56:28,396 of directly doing Alice arrow age equals 20 which is bad. 1024 00:56:29,606 --> 00:56:31,856 We are saying Alice setAge to 20. 1025 00:56:31,856 --> 00:56:35,386 We are sending the message setAge with the argument in 20 1026 00:56:35,386 --> 00:56:38,226 to Alice and we're setting the name to Alice 1027 00:56:38,926 --> 00:56:40,186 and similarly with Bob. 1028 00:56:40,306 --> 00:56:41,286 And then what greet [phonetic] is going 1029 00:56:41,286 --> 00:56:44,946 to do is use this S name and S age. 1030 00:56:44,946 --> 00:56:49,436 We're going to send those getter methods to get getter messages 1031 00:56:49,826 --> 00:56:52,136 to get the appropriate instance variables. 1032 00:56:52,136 --> 00:56:52,203 Yeah. 1033 00:56:53,516 --> 00:56:59,956 [ Inaudible Remark ] 1034 00:57:00,456 --> 00:57:03,366 Oh so, the only reason we can do that here is 1035 00:57:03,366 --> 00:57:06,766 because student alloc happens to return the student object. 1036 00:57:07,196 --> 00:57:10,366 And so we are then using that student object and initting it. 1037 00:57:10,686 --> 00:57:13,336 And that also returns the initialized student object. 1038 00:57:13,876 --> 00:57:17,466 SetAge doesn't return this student object. 1039 00:57:17,966 --> 00:57:21,076 If we do we could actually do that we can do like instead 1040 00:57:21,076 --> 00:57:24,386 of void, we can have it return the student object. 1041 00:57:25,516 --> 00:57:31,556 [ Pause ] 1042 00:57:32,056 --> 00:57:34,976 >> And then this is going to get into return self. 1043 00:57:34,976 --> 00:57:36,416 Self is going to be your keyword here. 1044 00:57:36,416 --> 00:57:36,976 We'll see it later. 1045 00:57:37,516 --> 00:57:42,516 [ Pause ] 1046 00:57:43,016 --> 00:57:52,000 [ Inaudible Remark ] 1047 00:57:52,746 --> 00:57:56,976 So here, are you saying why should we need-- 1048 00:57:57,516 --> 00:58:02,176 [ Inaudible Remark ] 1049 00:58:02,676 --> 00:58:05,996 So this is that you never pass but-- 1050 00:58:05,996 --> 00:58:07,436 you never pass objects by value. 1051 00:58:07,586 --> 00:58:09,816 You never handle objects as explicit values. 1052 00:58:10,066 --> 00:58:12,606 You're always going to go through a pointer to the object 1053 00:58:13,006 --> 00:58:14,126 which is why I say pretty-- 1054 00:58:14,126 --> 00:58:15,926 think of like NSString star 1055 00:58:15,926 --> 00:58:18,146 as the object not a pointer to the object. 1056 00:58:18,146 --> 00:58:22,176 Think of it as the object. 1057 00:58:22,176 --> 00:58:24,696 Except that if you modify it, then it's going to be modified 1058 00:58:24,806 --> 00:58:25,656 because it's a reference. 1059 00:58:26,326 --> 00:58:29,766 OK, so now we're returning self which is going 1060 00:58:29,766 --> 00:58:33,376 to allow us to do that nested. 1061 00:58:33,556 --> 00:58:40,956 Now we're free to do Alice setAge 20, setName Alice. 1062 00:58:41,516 --> 00:58:44,516 [ Pause ] 1063 00:58:45,016 --> 00:58:48,000 [ Inaudible Remark ] 1064 00:58:48,996 --> 00:58:50,416 We-- not yet. 1065 00:58:51,776 --> 00:58:54,286 The next example we'll be able to. 1066 00:58:55,906 --> 00:58:58,506 Just to point out one other thing that you might see 1067 00:58:58,506 --> 00:59:01,616 in like documentation or like example online or stuff. 1068 00:59:01,886 --> 00:59:06,896 So alloc init is such an incredibly common thing 1069 00:59:06,896 --> 00:59:09,166 like you alloc init-- you might be doing some 1070 00:59:09,166 --> 00:59:10,176 different initializer. 1071 00:59:10,416 --> 00:59:14,376 There are different initializers but using alloc and init is 1072 00:59:14,376 --> 00:59:16,856 so common that there's actually a shortcut-- 1073 00:59:17,516 --> 00:59:20,886 [ Pause ] 1074 00:59:21,386 --> 00:59:25,896 -- New, and so, new is going to sort of-- 1075 00:59:25,896 --> 00:59:30,526 or new is going to first allocate and then initialize. 1076 00:59:30,526 --> 00:59:33,426 So that does it in one step. 1077 00:59:34,236 --> 00:59:37,516 There are sort of-- well, this is the first 1078 00:59:37,516 --> 00:59:41,276 of three religious wars you'll hear today about objective-C 1079 00:59:41,526 --> 00:59:42,506 that there are a lot of people 1080 00:59:42,506 --> 00:59:45,036 who will say new is a perfectly fine thing, and there are lot 1081 00:59:45,036 --> 00:59:47,236 of people who will say you should absolutely never say new. 1082 00:59:47,426 --> 00:59:50,966 So, we don't care which you use, whether you want 1083 00:59:50,966 --> 00:59:53,426 to explicitly allocate and initialize or whatever. 1084 00:59:54,226 --> 00:59:56,226 [ Pause ] 1085 00:59:56,436 --> 00:59:59,506 OK? Questions on any of that? 1086 01:00:00,586 --> 01:00:00,926 Yes? 1087 01:00:01,226 --> 01:00:09,346 >> So does allocate initially reserve space on the key 1088 01:00:09,346 --> 01:00:11,196 for the object and then setting 1089 01:00:11,196 --> 01:00:12,976 on the instance variables on that? 1090 01:00:12,976 --> 01:00:14,456 >> Yeah, it is-- potentially other things 1091 01:00:14,456 --> 01:00:16,086 than setting instance variables. 1092 01:00:16,086 --> 01:00:19,166 If you wanted, you're going to find the initialization method 1093 01:00:19,166 --> 01:00:23,936 that like counts the number of objects of this type 1094 01:00:23,966 --> 01:00:24,596 that had been initialized. 1095 01:00:24,626 --> 01:00:25,976 But you should never handle an uninitialized object. 1096 01:00:26,516 --> 01:00:29,736 [ Pause ] 1097 01:00:30,236 --> 01:00:36,656 OK? So then this is going to be the next example 1098 01:00:36,656 --> 01:00:37,826 that we're going to want to use 1099 01:00:37,826 --> 01:00:41,366 but let's just look at the slide first. 1100 01:00:41,366 --> 01:00:46,416 So, Property so-- and this is going to be what we're going 1101 01:00:46,416 --> 01:00:49,236 to use to enable us to use .syntax. 1102 01:00:49,966 --> 01:00:55,166 We can somewhat ignore a lot of these keywords for now. 1103 01:00:55,376 --> 01:00:57,866 These assign, copy, strong, weak are things we're going 1104 01:00:57,866 --> 01:00:58,856 to deal with next week. 1105 01:00:59,686 --> 01:01:04,766 Strong and weak in particular are pretty much the only things 1106 01:01:04,766 --> 01:01:07,436 you really need to think about under ARC. 1107 01:01:08,426 --> 01:01:11,726 Those are memory management difficulties 1108 01:01:11,726 --> 01:01:13,996 that if you got those wrong, you can still leak things. 1109 01:01:15,936 --> 01:01:18,406 But it's not too bad. 1110 01:01:18,406 --> 01:01:19,536 It's especially better than needing 1111 01:01:19,536 --> 01:01:20,326 to keep track of everything. 1112 01:01:21,186 --> 01:01:23,856 Atomic and nonatomic are a different pair of things 1113 01:01:23,856 --> 01:01:25,466 that we'll get into and we don't mean readwrite. 1114 01:01:25,796 --> 01:01:27,356 We will talk about today. 1115 01:01:27,646 --> 01:01:29,926 So @property, new thing. 1116 01:01:30,736 --> 01:01:31,826 So look at the example. 1117 01:01:32,516 --> 01:01:39,636 [ Pause ] 1118 01:01:40,136 --> 01:01:40,886 Student-free. 1119 01:01:41,516 --> 01:01:44,896 [ Pause ] 1120 01:01:45,396 --> 01:01:51,026 OK. So looking at student.h, the only thing that is changed is 1121 01:01:51,656 --> 01:01:53,406 that we have added these two lines. 1122 01:01:54,236 --> 01:01:59,176 So, we have SetAppProperty and from each of those groups 1123 01:01:59,176 --> 01:02:03,396 that we saw in the-- on that property slide, 1124 01:02:03,956 --> 01:02:06,536 we are picking a sign from the first group, nonatomic come 1125 01:02:06,536 --> 01:02:08,446 in second group, and readwrite from the third group. 1126 01:02:09,296 --> 01:02:12,076 And then we're saying that this instance variable is called 1127 01:02:12,126 --> 01:02:12,726 int age. 1128 01:02:13,606 --> 01:02:17,636 So, assign again, you can ignore nonatomic. 1129 01:02:17,636 --> 01:02:21,636 This is just saying that like you can assume 1130 01:02:21,636 --> 01:02:24,046 that we're not dealing with any multi-threaded type 1131 01:02:24,726 --> 01:02:26,136 messiness here. 1132 01:02:26,376 --> 01:02:28,846 You don't have to deal with the overhead of making sure 1133 01:02:28,846 --> 01:02:32,276 that whenever we modify this age instance field 1134 01:02:32,756 --> 01:02:35,636 that you don't have to deal with making sure it's atomic. 1135 01:02:35,926 --> 01:02:40,286 So atomic just means like it happens instantaneously. 1136 01:02:40,396 --> 01:02:41,366 We don't have to deal with that. 1137 01:02:42,276 --> 01:02:45,436 So, and readwrite, this is probably 1138 01:02:45,906 --> 01:02:48,176 or in this class you're pretty much only going 1139 01:02:48,176 --> 01:02:51,676 to using nonatomic. 1140 01:02:51,726 --> 01:02:58,036 Readwrite is one that if it's readwrite then this property is 1141 01:02:58,036 --> 01:02:59,986 expecting a setter and a getter. 1142 01:03:00,296 --> 01:03:02,666 If it's read-only, it's expecting just a getter. 1143 01:03:03,486 --> 01:03:05,996 So since we want to be able to both write to age 1144 01:03:05,996 --> 01:03:08,176 and get the age, then we say its readwrite 1145 01:03:08,366 --> 01:03:09,426 and some it will lead for name. 1146 01:03:09,996 --> 01:03:13,816 OK, so then these are the same. 1147 01:03:15,266 --> 01:03:19,206 Back in student.m we see the same. 1148 01:03:19,706 --> 01:03:24,406 But looking at main.m, the fact 1149 01:03:24,606 --> 01:03:27,256 that these are now properties allows us 1150 01:03:27,256 --> 01:03:31,076 to say Alice.age equals 20 and Alice.name equals @Alice. 1151 01:03:32,476 --> 01:03:37,046 So what do property does for us is says 1152 01:03:37,346 --> 01:03:42,806 that since we said there is a property called age then 1153 01:03:42,806 --> 01:03:47,736 Alice.age is by the conventions that are now going to be 1154 01:03:47,736 --> 01:03:49,546 like something you should absolutely follow, 1155 01:03:49,906 --> 01:03:52,376 Alice.age is underneath the hood going 1156 01:03:52,376 --> 01:03:56,876 to be translated to Alice setAge 20. 1157 01:03:58,546 --> 01:04:03,496 And this is going to be Alice.name @Alice. 1158 01:04:04,986 --> 01:04:07,026 So this is what properties have done for us. 1159 01:04:07,106 --> 01:04:08,796 It's allowed us to access 1160 01:04:08,796 --> 01:04:11,706 and set instance variables using .notation. 1161 01:04:12,086 --> 01:04:15,186 Instead of having to go through this set name 1162 01:04:15,186 --> 01:04:20,626 and setAge method or message passing. 1163 01:04:20,626 --> 01:04:24,546 It's somewhat important and yet at the same time not really 1164 01:04:24,546 --> 01:04:29,696 that important to remember that we are going 1165 01:04:29,736 --> 01:04:31,676 through the overhead of a message pass. 1166 01:04:31,746 --> 01:04:34,936 So it's not like in regular C, this is not a struct, 1167 01:04:35,536 --> 01:04:38,846 so you would not be able to use .notation 1168 01:04:38,846 --> 01:04:40,086 on a pointer to a struct. 1169 01:04:40,086 --> 01:04:45,826 This is an object, this .notation is calling a method 1170 01:04:46,436 --> 01:04:50,926 and so there's some overhead to that but again its Objective-C, 1171 01:04:51,366 --> 01:04:53,196 let the compiler handler-- 1172 01:04:53,196 --> 01:04:55,656 let the compiler handle any optimizations. 1173 01:04:55,656 --> 01:04:58,416 Don't really worry about the overhead of message passings. 1174 01:04:58,946 --> 01:05:06,206 Then down here at greet, we see s.name and s.age 1175 01:05:06,446 --> 01:05:11,126 which are equivalent to just S name and S age. 1176 01:05:11,306 --> 01:05:13,506 And so this is why I said before, 1177 01:05:13,566 --> 01:05:15,196 you should follow the convention 1178 01:05:15,196 --> 01:05:18,206 that like the getter is just called name and not getname, 1179 01:05:18,716 --> 01:05:20,406 because s.name is going 1180 01:05:20,406 --> 01:05:23,206 to expect the getter to be called name. 1181 01:05:23,586 --> 01:05:25,786 And if it's not, you're not going to be able 1182 01:05:27,136 --> 01:05:28,866 to use the property as expected. 1183 01:05:29,516 --> 01:05:37,796 [ Inaudible Remark ] 1184 01:05:38,296 --> 01:05:41,086 Wait till the next example. 1185 01:05:41,666 --> 01:05:41,956 [laughs] Yeah. 1186 01:05:42,516 --> 01:05:50,056 [ Inaudible Remark ] 1187 01:05:50,556 --> 01:05:51,526 I changed that. 1188 01:05:51,776 --> 01:05:53,456 They should always have it. 1189 01:05:53,456 --> 01:05:57,226 Yeah. [Inaudible Remark] So the reason for this is 1190 01:05:57,226 --> 01:06:01,316 that NSObject's init method, so init is inherited from NSObject. 1191 01:06:01,766 --> 01:06:04,996 And we see that Student is directly inheriting 1192 01:06:04,996 --> 01:06:09,276 from NSObject and so because the init method 1193 01:06:09,276 --> 01:06:16,076 of NSObject does nothing, then there is no difference 1194 01:06:16,076 --> 01:06:19,176 between Student alloc and Student alloc init, 1195 01:06:19,176 --> 01:06:20,636 those two things are going to be the same. 1196 01:06:21,556 --> 01:06:25,246 But you should always handle initialized object if-- 1197 01:06:25,946 --> 01:06:28,476 I doubt NSObject would do this, 1198 01:06:28,476 --> 01:06:30,966 but if someday NSObject changes initialize method 1199 01:06:30,966 --> 01:06:34,716 to now keep track of something, then this code will break 1200 01:06:34,716 --> 01:06:36,356 because you did not initialize that object. 1201 01:06:36,806 --> 01:06:39,486 Or alternatively, if inside of Student, 1202 01:06:39,876 --> 01:06:44,426 I decide to overrride the init method and have it do something, 1203 01:06:46,076 --> 01:06:48,236 define my own init method, 1204 01:06:48,376 --> 01:06:52,276 we'll actually see examples of that later. 1205 01:06:53,416 --> 01:06:55,886 But if I were to define my own init method, 1206 01:06:56,146 --> 01:06:59,996 then all of a sudden, everything in main.m would stop working 1207 01:06:59,996 --> 01:07:01,776 because it did not initialize the Students. 1208 01:07:02,666 --> 01:07:05,766 So always-- even if you know you're inheriting 1209 01:07:05,766 --> 01:07:07,926 from NSObject, still initialize it. 1210 01:07:08,196 --> 01:07:10,306 Even if it's because someone later on coming 1211 01:07:10,306 --> 01:07:12,486 around reading your code is going to be like, "Wait, 1212 01:07:12,486 --> 01:07:15,216 this isn't initialized," now, they have to go check 1213 01:07:15,216 --> 01:07:16,126 to make sure that it-- 1214 01:07:16,166 --> 01:07:19,116 the initialization isn't actually going to do anything, 1215 01:07:19,116 --> 01:07:21,496 it's always initialized. 1216 01:07:22,516 --> 01:07:25,696 [ Pause ] 1217 01:07:26,196 --> 01:07:28,676 So one last. 1218 01:07:29,916 --> 01:07:31,566 OK. Any other questions? 1219 01:07:32,516 --> 01:07:35,446 [ Pause ] 1220 01:07:35,946 --> 01:07:39,836 OK. Then here. 1221 01:07:43,636 --> 01:07:52,786 OK. So synthesize, this is what in the past was used 1222 01:07:52,826 --> 01:07:55,356 to do exactly what you just said, that getting rid 1223 01:07:55,356 --> 01:07:56,436 of the getters and setters. 1224 01:07:56,846 --> 01:08:02,946 So, what-- let's look at Student 4. 1225 01:08:03,516 --> 01:08:15,936 [ Pause ] 1226 01:08:16,436 --> 01:08:23,516 So we have gotten rid of the explicit declarations 1227 01:08:23,516 --> 01:08:27,946 of the setters and getters from here, just deleted them. 1228 01:08:28,906 --> 01:08:30,216 They were redundant to begin with. 1229 01:08:30,756 --> 01:08:35,216 And Student-- or student.m, we've now gotten rid 1230 01:08:35,216 --> 01:08:37,096 of the implementations of those things. 1231 01:08:38,026 --> 01:08:40,096 In the past, we used init do 1232 01:08:40,096 --> 01:08:46,036 like @synthesize age equals underscore age messiness. 1233 01:08:46,646 --> 01:08:49,056 The reason for that is because the compiler didn't use 1234 01:08:49,056 --> 01:08:51,236 to be smart enough to recognize that if there's a property 1235 01:08:51,236 --> 01:08:53,916 in here, then it should automatically be in here. 1236 01:08:54,586 --> 01:08:56,096 Now, it is smart enough. 1237 01:08:56,096 --> 01:08:59,886 So now, the property is enough to say 1238 01:08:59,886 --> 01:09:02,026 that we want an instance variable called, 1239 01:09:02,656 --> 01:09:05,346 we're actually using the defaults, 1240 01:09:05,776 --> 01:09:08,466 and this is again why we come back to underscore, the defaults 1241 01:09:08,586 --> 01:09:12,706 of this line is, we want an instance variable called 1242 01:09:12,936 --> 01:09:17,336 underscore age that has a setter called setAge 1243 01:09:17,516 --> 01:09:19,476 and a setter-- a getter called age. 1244 01:09:20,016 --> 01:09:23,636 And that setter and getter is going 1245 01:09:23,636 --> 01:09:27,876 to be implemented using these particular semantics 1246 01:09:28,196 --> 01:09:33,856 but you don't have to worry about assign and nonatomic yet. 1247 01:09:34,236 --> 01:09:40,446 This also means that before, even though we had set assign, 1248 01:09:40,446 --> 01:09:41,696 and nonatomic, and readwrite, 1249 01:09:42,636 --> 01:09:44,556 you are allowed to override those. 1250 01:09:45,606 --> 01:09:49,506 And so before in the previous example 1251 01:09:49,506 --> 01:09:51,696 when we had explicitly defined the setAge, 1252 01:09:52,136 --> 01:09:55,636 setAge was not necessarily following these semantics. 1253 01:09:56,076 --> 01:09:58,936 It happened to be because that's how we implement it. 1254 01:09:58,936 --> 01:10:02,256 We didn't implement it carrying 1255 01:10:02,256 --> 01:10:03,566 about whether it was multithreaded 1256 01:10:03,566 --> 01:10:04,406 and all that stuff. 1257 01:10:05,086 --> 01:10:09,486 So you are allowed to override these behaviors. 1258 01:10:09,896 --> 01:10:13,746 I actually think Student 5 might go into that. 1259 01:10:14,516 --> 01:10:18,746 [ Pause ] 1260 01:10:19,246 --> 01:10:23,866 So Student 5, looking at student.h, again, 1261 01:10:23,866 --> 01:10:25,226 we still have age and name. 1262 01:10:26,206 --> 01:10:30,116 Now, in student.m, we still do not synthesize 1263 01:10:30,836 --> 01:10:35,596 but we just happen to decide to overwrite the setName method. 1264 01:10:35,596 --> 01:10:41,936 This was David's example of if the name happens to be David, 1265 01:10:41,986 --> 01:10:44,186 then change it to Dummy, otherwise, 1266 01:10:44,486 --> 01:10:45,826 do the original behavior. 1267 01:10:46,776 --> 01:10:52,026 So here, we have overwritten what the default setting would 1268 01:10:52,026 --> 01:10:56,466 do if we just did copy nonatomic. 1269 01:10:57,576 --> 01:11:02,446 But, if we also decide that we wanted to-- 1270 01:11:03,516 --> 01:11:14,016 [ Pause ] 1271 01:11:14,516 --> 01:11:19,746 If we decided that we wanted to override the getter, 1272 01:11:20,556 --> 01:11:26,426 and say return name, now, because of the way things are, 1273 01:11:26,776 --> 01:11:29,396 we do need to explicitly synthesize. 1274 01:11:30,106 --> 01:11:31,476 So, now, we would need 1275 01:11:31,476 --> 01:11:36,146 to say synthesize name equals underscore name. 1276 01:11:36,596 --> 01:11:38,866 And those should go away. 1277 01:11:40,036 --> 01:11:40,416 All right. 1278 01:11:40,486 --> 01:11:43,106 It's only if you happen to be overriding both the getter 1279 01:11:43,106 --> 01:11:46,246 and the setter that we need to synthesize the variable again. 1280 01:11:46,976 --> 01:11:48,516 Otherwise, it wouldn't know 1281 01:11:48,516 --> 01:11:50,666 that this underscore name variable exists. 1282 01:11:51,856 --> 01:11:55,796 This behavior is because of some backwards compatibility issues 1283 01:11:55,796 --> 01:11:57,836 but it's the way it is. 1284 01:11:58,516 --> 01:12:04,116 [ Inaudible Remark ] 1285 01:12:04,616 --> 01:12:07,686 But if you use property and you say readwrite, 1286 01:12:07,686 --> 01:12:10,516 if it is a readwrite property, the getter is-- 1287 01:12:10,576 --> 01:12:13,466 getters and setters are automatically defined before you 1288 01:12:13,726 --> 01:12:15,446 unless you decide to override them. 1289 01:12:15,976 --> 01:12:18,816 And if you override them both, then you need 1290 01:12:18,816 --> 01:12:22,226 to synthesize again, because otherwise it doesn't know 1291 01:12:22,226 --> 01:12:23,506 about that instance variable. 1292 01:12:24,156 --> 01:12:30,256 It's like looking at student.h, we see property age 1293 01:12:30,256 --> 01:12:32,936 and property name, we don't see anything about underscore age 1294 01:12:32,936 --> 01:12:35,956 and underscore name, and that's part 1295 01:12:35,956 --> 01:12:38,126 of the reason why we need to synthesize. 1296 01:12:38,126 --> 01:12:41,066 It's messy but rarely are you going 1297 01:12:41,066 --> 01:12:43,296 to be overriding both the getter and the setter anyway. 1298 01:12:43,986 --> 01:12:45,296 You might be overriding them in-- 1299 01:12:45,296 --> 01:12:48,776 if you are like trying to debug something and you add NSLog 1300 01:12:48,776 --> 01:12:51,286 to both the getter and the setter, in which case, 1301 01:12:51,846 --> 01:12:55,286 remember that now, you're going to need to synthesize or self, 1302 01:12:55,286 --> 01:12:56,286 it'll [inaudible] you. 1303 01:12:58,236 --> 01:12:58,936 Questions? 1304 01:12:59,516 --> 01:13:05,416 [ Inaudible Remark ] 1305 01:13:05,916 --> 01:13:06,986 Yeah. See? 1306 01:13:06,986 --> 01:13:08,686 It-- well, if I get rid of the assign, now, 1307 01:13:08,686 --> 01:13:10,026 I'm going to get a bunch of errors. 1308 01:13:10,666 --> 01:13:15,926 If I now get rid of this setter, I don't have any errors anymore, 1309 01:13:17,136 --> 01:13:20,656 because as long as I only override one of them, it's fine. 1310 01:13:21,356 --> 01:13:25,326 It's also important just to recognize synthesize 1311 01:13:25,326 --> 01:13:28,076 because you're going to see it in a lot of prior examples, 1312 01:13:28,136 --> 01:13:32,386 like a lot of online things you find will use synthesize, 1313 01:13:32,386 --> 01:13:35,656 'cause it's a relatively new thing. 1314 01:13:36,656 --> 01:13:38,866 But you don't need to use it. 1315 01:13:40,926 --> 01:13:41,456 OK. 1316 01:13:42,516 --> 01:13:48,916 [ Pause ] 1317 01:13:49,416 --> 01:13:51,856 OK. So, init methods. 1318 01:13:52,406 --> 01:13:55,256 So up till now, we just used init. 1319 01:13:55,926 --> 01:13:57,606 Remember, you should always initialize something 1320 01:13:57,826 --> 01:14:00,126 but you don't need to initialize it with just init. 1321 01:14:00,126 --> 01:14:03,186 You can define your own initialization methods. 1322 01:14:03,186 --> 01:14:07,646 And if you look at-- well, when you're actually doing iOS, 1323 01:14:07,646 --> 01:14:08,926 you're going to be dealing with a bunch 1324 01:14:08,926 --> 01:14:10,346 of other initialization methods. 1325 01:14:10,916 --> 01:14:14,696 But the convention is that the initialization methods are 1326 01:14:14,696 --> 01:14:19,256 always going to start with lower case init, and then, the-- 1327 01:14:19,256 --> 01:14:24,356 so, reading this method, we have an instance method 'cause it's 1328 01:14:24,356 --> 01:14:24,876 a dash. 1329 01:14:25,766 --> 01:14:31,346 It's going to return an ID, so this is also convention. 1330 01:14:31,636 --> 01:14:35,126 We know that it is necessarily returning a Student star, 1331 01:14:36,326 --> 01:14:38,006 and remember that ID is just sort 1332 01:14:38,006 --> 01:14:39,856 of like a catch all for all objects. 1333 01:14:40,376 --> 01:14:42,296 The convention 1334 01:14:42,296 --> 01:14:44,326 for initialization methods is that they return ID. 1335 01:14:44,326 --> 01:14:48,986 Then the-- this is pretty much the convention too 1336 01:14:49,206 --> 01:14:54,886 that we have initWithName: and we pass it a name. 1337 01:14:55,236 --> 01:14:57,946 And notice now, we are passing a second argument, 1338 01:14:58,236 --> 01:14:59,856 so space andAge:age. 1339 01:14:59,856 --> 01:15:05,976 So the name of this method is initWithName:andAge:. 1340 01:15:05,976 --> 01:15:08,936 That name and age are arguments. 1341 01:15:08,986 --> 01:15:10,486 Those are not part of the name of method. 1342 01:15:11,466 --> 01:15:13,796 So, we already see how these names can get pretty long. 1343 01:15:14,536 --> 01:15:16,586 Believe me when I say that there are method names that are 1344 01:15:16,586 --> 01:15:22,476 like four times longer than this in iOS dealings 1345 01:15:22,576 --> 01:15:24,576 that you will be using. 1346 01:15:26,556 --> 01:15:32,056 So, one other-- I don't know. 1347 01:15:33,676 --> 01:15:34,076 Questions. 1348 01:15:34,076 --> 01:15:34,416 [Inaudible Remark] Yes. 1349 01:15:34,416 --> 01:15:37,476 It's very similar to void star except it's dealing 1350 01:15:37,476 --> 01:15:39,686 with objects instead of general pointers. 1351 01:15:40,216 --> 01:15:43,126 And we'll see ID in other places too. 1352 01:15:43,976 --> 01:15:45,326 And it's also similar to voidstar 1353 01:15:45,326 --> 01:15:48,886 and that automatic casting happens. 1354 01:15:51,016 --> 01:15:51,896 [Inaudible Remark] This whole thing? 1355 01:15:52,116 --> 01:15:57,356 OK. So, we have instance method. 1356 01:15:57,356 --> 01:16:00,946 It is returning an ID so that's just the way it is. 1357 01:16:00,946 --> 01:16:03,226 If you wanted, you could say Student star, 1358 01:16:03,606 --> 01:16:06,156 but you shouldn't-- you should say ID 1359 01:16:06,156 --> 01:16:08,986 because any initialization method pretty much returns ID, 1360 01:16:10,456 --> 01:16:14,736 then the convention is that you're going to init and then 1361 01:16:15,676 --> 01:16:17,406 with is also pretty much the convention. 1362 01:16:17,406 --> 01:16:21,506 The-- any colon-- you can count the colons 1363 01:16:21,506 --> 01:16:23,286 to determine the number of arguments to your function. 1364 01:16:23,806 --> 01:16:25,496 So here we see two colons. 1365 01:16:25,696 --> 01:16:27,686 That means we know they're going to be two arguments. 1366 01:16:28,956 --> 01:16:30,946 The first argument is called name, 1367 01:16:30,946 --> 01:16:32,356 and a subtype NSString star. 1368 01:16:32,826 --> 01:16:35,186 The second argument is called age, and a subtype int. 1369 01:16:36,156 --> 01:16:39,646 So, when we want to actually call this function, 1370 01:16:39,816 --> 01:16:43,456 we might say like, well, first, we allocate a Student 1371 01:16:44,036 --> 01:16:53,466 and then we say, Student initWithName:@bob andAge:21, 1372 01:16:54,016 --> 01:16:59,126 and we'll see an example of that 1373 01:16:59,366 --> 01:17:02,616 in another Students 4 or 5 or whatever. 1374 01:17:03,516 --> 01:17:16,736 [ Inaudible Remark ] 1375 01:17:17,236 --> 01:17:22,396 So, the answer is no, but that should never be the case 1376 01:17:22,996 --> 01:17:24,566 because if the variables are different, 1377 01:17:24,656 --> 01:17:26,086 this naming scheme should be different. 1378 01:17:26,546 --> 01:17:29,726 This is how you name methods in like-- 1379 01:17:29,836 --> 01:17:33,366 all method names are very long and explicit in Objective-C. 1380 01:17:33,636 --> 01:17:36,246 And so, if we decided that instead, 1381 01:17:36,246 --> 01:17:38,466 we wanted to just initialize with the name, 1382 01:17:38,676 --> 01:17:42,206 then we would have initWithName method without the andAge. 1383 01:17:42,466 --> 01:17:45,586 If we wanted to just do name, we would've initWithAge method 1384 01:17:45,946 --> 01:17:50,916 without the andName or whatever. 1385 01:17:50,916 --> 01:17:50,983 Yeah. 1386 01:17:51,516 --> 01:17:54,916 [ Inaudible Remark ] 1387 01:17:55,416 --> 01:17:57,006 That was a typo. 1388 01:17:57,406 --> 01:17:58,196 That has been fixed. 1389 01:17:59,126 --> 01:18:00,746 These will be uploaded at the end. 1390 01:18:01,496 --> 01:18:02,826 There are some changes. 1391 01:18:03,426 --> 01:18:06,146 Other questions. 1392 01:18:07,166 --> 01:18:07,316 Yeah. 1393 01:18:08,516 --> 01:18:13,866 [ Inaudible Remark ] 1394 01:18:14,366 --> 01:18:15,996 Yeah. You would just put more 1395 01:18:16,086 --> 01:18:19,786 with andGender, andYear and whatever. 1396 01:18:20,526 --> 01:18:25,136 The number of colons specifies-- in theory, we wouldn't-- 1397 01:18:25,316 --> 01:18:30,176 we don't need to say andAge like a valid method name is init, 1398 01:18:30,856 --> 01:18:34,156 colon, colon which-- because there are two colons, 1399 01:18:34,156 --> 01:18:37,636 we expect there are going to be two arguments, and so we call it 1400 01:18:37,636 --> 01:18:41,966 with like init:bob:20, but that's not what you should do 1401 01:18:41,966 --> 01:18:44,586 in Objective-C, you should explicitly name all 1402 01:18:44,586 --> 01:18:45,436 of your parameters. 1403 01:18:45,686 --> 01:18:50,526 So, initWithName:whatever, andAge:whatever. 1404 01:18:52,516 --> 01:18:58,476 [ Inaudible Remark ] 1405 01:18:58,976 --> 01:19:03,886 You cannot by default pass in a dictionary or object or anything 1406 01:19:03,886 --> 01:19:06,276 like that, this is pretty much the only way you can run it, 1407 01:19:07,126 --> 01:19:10,176 unless you happened to define initialization method 1408 01:19:10,176 --> 01:19:14,016 that like takes what we'll see later like in NSDictionary, 1409 01:19:14,526 --> 01:19:17,176 but that's up to you to define such an initialization method. 1410 01:19:17,636 --> 01:19:21,006 It's-- but you pretty much should-- 1411 01:19:21,006 --> 01:19:22,026 this is the way it should be. 1412 01:19:22,416 --> 01:19:23,966 And also, if you follow this convention, 1413 01:19:23,966 --> 01:19:26,996 I'm pretty sure Xcode is going to give you some like-- 1414 01:19:27,426 --> 01:19:30,616 some more advanced tips in Auto Completion and stuff. 1415 01:19:31,936 --> 01:19:34,426 The convention being like they should return ID, 1416 01:19:34,836 --> 01:19:36,606 they should start with the four letters, init. 1417 01:19:37,416 --> 01:19:41,906 And when someone is reading your code, they expect you 1418 01:19:41,906 --> 01:19:44,256 to initialize something so they should see the four letters, 1419 01:19:44,256 --> 01:19:44,656 init. 1420 01:19:49,506 --> 01:19:52,326 OK. Looking at this example. 1421 01:19:53,516 --> 01:19:58,576 [ Pause ] 1422 01:19:59,076 --> 01:20:01,546 Six. OK. 1423 01:20:02,516 --> 01:20:11,236 [ Pause ] 1424 01:20:11,736 --> 01:20:16,166 OK. So, in student.h, we see we are now declaring a new method, 1425 01:20:16,836 --> 01:20:18,156 exactly what we saw before. 1426 01:20:18,626 --> 01:20:22,826 Now that we have said that we are using this method, 1427 01:20:23,306 --> 01:20:27,676 we need to implement that method in the .m file. 1428 01:20:27,866 --> 01:20:31,916 So, here, let's first look at the initWithName. 1429 01:20:32,466 --> 01:20:34,846 So, this is a very common pattern. 1430 01:20:35,946 --> 01:20:37,926 Whenever you define your own initializer, 1431 01:20:38,016 --> 01:20:42,706 this is pretty much the pattern you want to take where the-- 1432 01:20:43,516 --> 01:20:50,186 [ Pause ] 1433 01:20:50,686 --> 01:20:52,676 -- first, second-- let's say this first. 1434 01:20:52,676 --> 01:20:56,176 So, this is somewhat weird from other languages 1435 01:20:56,176 --> 01:20:58,696 where like self is just sort of like a keyword. 1436 01:20:58,946 --> 01:21:01,106 Here, self is a variable and you're assigning 1437 01:21:01,106 --> 01:21:04,916 to that variable the result of initializing your super class. 1438 01:21:05,506 --> 01:21:08,076 So, this is the part of the pattern 1439 01:21:08,076 --> 01:21:09,436 that you pretty much always do. 1440 01:21:09,916 --> 01:21:11,966 So, just because like-- 1441 01:21:12,796 --> 01:21:15,336 or I happened to inherit from NSObject 1442 01:21:15,336 --> 01:21:17,566 which its initialization method does nothing, 1443 01:21:17,796 --> 01:21:19,316 but imagine that it does do something. 1444 01:21:19,936 --> 01:21:23,866 So, just because I know how I want 1445 01:21:23,866 --> 01:21:27,106 to be initialized doesn't mean I know how my parent class wants 1446 01:21:27,106 --> 01:21:27,836 to be initialized. 1447 01:21:27,836 --> 01:21:30,346 So, you should always call your parent-- 1448 01:21:30,346 --> 01:21:34,206 initializer of parent class. 1449 01:21:34,316 --> 01:21:37,026 So, the reason we assigned to self and do this whole 1450 01:21:37,026 --> 01:21:41,166 if self equals super init thing is under some bizarre scenario 1451 01:21:41,166 --> 01:21:44,486 where initializing the super class manages to return nil 1452 01:21:44,486 --> 01:21:47,976 or something, like initialization went wrong, 1453 01:21:48,506 --> 01:21:50,496 then we don't want to do these two things. 1454 01:21:51,436 --> 01:21:53,676 As an example, maybe we just happened 1455 01:21:53,676 --> 01:21:57,896 to define the initializer as like only five objects 1456 01:21:57,896 --> 01:21:59,926 of this class type should ever be initialized. 1457 01:22:00,126 --> 01:22:01,636 After five, it should just fail. 1458 01:22:02,436 --> 01:22:07,606 And so-- then when they tried to initialize, if it's after five, 1459 01:22:07,706 --> 01:22:10,326 presumably this super init is going to fail 1460 01:22:10,606 --> 01:22:16,986 and self will be nil and then will just return self. 1461 01:22:16,986 --> 01:22:17,656 Yes? [Inaudible Remark] Yes. 1462 01:22:17,656 --> 01:22:22,516 Yes, yes. Self, this are two things you see in languages, 1463 01:22:22,516 --> 01:22:26,126 there is no this in Objective-C, they just call it self. 1464 01:22:26,246 --> 01:22:30,036 It means like-- it means this current object. 1465 01:22:30,216 --> 01:22:36,686 So, when I say-- when I have a Student, 1466 01:22:36,686 --> 01:22:39,066 like I just allocated the Student and then I passed 1467 01:22:39,356 --> 01:22:42,006 that Student the message initWithName, whatever, 1468 01:22:42,506 --> 01:22:46,466 then self refers to that Student I just passed the message to. 1469 01:22:47,786 --> 01:22:50,026 And so, similarly, self.age 1470 01:22:50,566 --> 01:22:57,156 which is also equivalent to self setAge, age. 1471 01:22:58,246 --> 01:23:02,516 So, self.age refers to this student. 1472 01:23:03,486 --> 01:23:07,216 We want to set our own age instance variable to age. 1473 01:23:09,516 --> 01:23:18,686 [ Inaudible Remark ] 1474 01:23:19,186 --> 01:23:21,296 Which do you need spell out? 1475 01:23:21,526 --> 01:23:21,806 Spell out. 1476 01:23:22,776 --> 01:23:23,626 [Inaudible Remark] This? 1477 01:23:24,206 --> 01:23:31,336 So, this gets into that-- there should always be-- 1478 01:23:31,336 --> 01:23:35,096 and you can look up these exact words designated initializer. 1479 01:23:35,776 --> 01:23:39,686 So, not really going to go into deep detail here, but, 1480 01:23:40,506 --> 01:23:43,586 every class should have exactly one designated initializer. 1481 01:23:44,346 --> 01:23:46,766 And this is, in other languages, you might see it 1482 01:23:46,766 --> 01:23:49,326 as like you define one constructor, 1483 01:23:49,466 --> 01:23:50,986 that sort of all other constructors 1484 01:23:50,986 --> 01:23:52,066 that you have called. 1485 01:23:53,296 --> 01:23:55,306 And so here, we decide 1486 01:23:55,306 --> 01:23:59,066 that initWithName should be our designated initializer, 1487 01:23:59,506 --> 01:24:03,186 which means that init needs to call our designated initializer. 1488 01:24:03,616 --> 01:24:14,246 If we then defined a (id)initWithAge method, 1489 01:24:16,456 --> 01:24:25,736 that should be int, then this must also call our designated 1490 01:24:25,736 --> 01:24:30,156 initializer and we'll use the defaults above, 1491 01:24:30,936 --> 01:24:33,636 beyond andAge, age. 1492 01:24:40,636 --> 01:24:42,466 So, there should always be one initializer 1493 01:24:42,466 --> 01:24:44,166 which is your designated initializer. 1494 01:24:44,866 --> 01:24:48,626 And also, that designated initializer needs 1495 01:24:48,626 --> 01:24:50,376 to call the designated initializer 1496 01:24:50,376 --> 01:24:51,646 of your parent class. 1497 01:24:52,466 --> 01:24:53,646 So, notice that init 1498 01:24:53,646 --> 01:24:55,766 and initWithAge are not calling super init, 1499 01:24:56,096 --> 01:24:57,666 it's only our designated initializer 1500 01:24:57,666 --> 01:24:58,806 which is calling super init. 1501 01:24:59,866 --> 01:25:04,556 So that's just-- if you start to find your own initializer, 1502 01:25:04,556 --> 01:25:06,376 just make sure you follow this convention 1503 01:25:06,376 --> 01:25:09,106 and you can remember just googling designated initializer. 1504 01:25:09,556 --> 01:25:16,466 And also notice that I should not do this. 1505 01:25:17,036 --> 01:25:18,856 Why is it? 1506 01:25:19,136 --> 01:25:23,416 I should not do this because this is not appropriately 1507 01:25:23,416 --> 01:25:24,096 setting self. 1508 01:25:25,026 --> 01:25:29,386 So, we want to set self to whatever that happens 1509 01:25:29,386 --> 01:25:31,586 to return and then return self. 1510 01:25:32,366 --> 01:25:34,366 [ Pause ] 1511 01:25:34,716 --> 01:25:35,426 Questions? 1512 01:25:36,906 --> 01:25:39,356 And then going back to main. 1513 01:25:40,036 --> 01:25:44,536 Now, we see that all in one line we're allocating a student, 1514 01:25:44,606 --> 01:25:46,926 initializing it with a name Alice and the age 20. 1515 01:25:53,496 --> 01:25:55,086 >> So the things we're allowing is super-- 1516 01:25:55,086 --> 01:25:55,796 >> In here? 1517 01:25:55,826 --> 01:25:55,893 >> Yeah. 1518 01:25:56,016 --> 01:26:02,526 >> So, imagine we are-- go back to the example from a while ago 1519 01:26:02,526 --> 01:26:04,876 where were have like NSObject and we have person, 1520 01:26:04,876 --> 01:26:06,466 then we have student, then we've 8th grader. 1521 01:26:07,246 --> 01:26:10,036 So, I want to define a new initialization method 1522 01:26:10,036 --> 01:26:15,616 for 8th grader and I decide that to initialize it like say, 1523 01:26:15,616 --> 01:26:17,476 it has an instant 8th graders. 1524 01:26:17,546 --> 01:26:18,576 Let say kindergardener. 1525 01:26:18,936 --> 01:26:21,826 So, kindergardener has an instance variable favorite color 1526 01:26:22,216 --> 01:26:26,556 and so we decided that like the default initialize-- 1527 01:26:26,636 --> 01:26:28,466 the default value for that instance variable should 1528 01:26:28,466 --> 01:26:28,946 be blue. 1529 01:26:29,556 --> 01:26:32,526 So, we define an initializer that says, 1530 01:26:32,926 --> 01:26:38,176 "That should be blue" except if we don't then call super init, 1531 01:26:38,476 --> 01:26:42,016 super now refers to, if we are a kindergarderner, 1532 01:26:42,016 --> 01:26:43,556 super refers to student. 1533 01:26:44,106 --> 01:26:47,406 And so if we don't call super init then we're not initializing 1534 01:26:47,406 --> 01:26:49,936 all these instance variables that happened to come 1535 01:26:50,256 --> 01:26:52,986 from the student class, in the person class, 1536 01:26:52,986 --> 01:26:54,506 in the NSObjects class. 1537 01:26:55,166 --> 01:27:00,596 So, you should always initialize your superclass. 1538 01:27:01,256 --> 01:27:03,436 Similar to like you should always initialize any object 1539 01:27:03,436 --> 01:27:05,686 that you allocate, you should always initialize your 1540 01:27:05,686 --> 01:27:10,376 superclass and these two methods happen 1541 01:27:10,376 --> 01:27:11,786 to initialize the superclass 1542 01:27:12,166 --> 01:27:14,396 by calling the designated initializer 1543 01:27:14,656 --> 01:27:16,976 which initializes the superclass. 1544 01:27:17,586 --> 01:27:20,826 But again, this pattern like this is the pattern 1545 01:27:20,826 --> 01:27:23,556 for writing your own initializer. 1546 01:27:23,866 --> 01:27:28,516 So, we should almost always copy and paste this and then 1547 01:27:28,516 --> 01:27:30,166 like in these curly braces is 1548 01:27:30,166 --> 01:27:32,176 where you set your instance variables 1549 01:27:32,176 --> 01:27:34,406 or NSLog whenever it is you want an NSLog. 1550 01:27:35,396 --> 01:27:37,396 [ Inaudible Remark ] 1551 01:27:37,776 --> 01:27:37,876 >> Yeah. 1552 01:27:38,516 --> 01:27:47,616 [ Pause ] 1553 01:27:48,116 --> 01:27:50,596 'Cause there might be something in that superclass that is 1554 01:27:50,596 --> 01:27:52,946 like essential for everything else to work. 1555 01:27:53,516 --> 01:28:03,886 [ Pause ] 1556 01:28:04,386 --> 01:28:04,976 Any other questions? 1557 01:28:05,516 --> 01:28:12,636 [ Inaudible Remark ] 1558 01:28:13,136 --> 01:28:15,646 >> Why does init with age not needed? 1559 01:28:16,276 --> 01:28:18,596 Because it's calling init with name and age. 1560 01:28:19,036 --> 01:28:22,476 It's calling this method which itself call super init, OK. 1561 01:28:24,516 --> 01:28:28,896 [ Pause ] 1562 01:28:29,396 --> 01:28:31,056 OK. We'll take the five minute break. 1563 01:28:33,016 --> 01:28:37,766 OK. So, am I-- am I now louder? 1564 01:28:39,706 --> 01:28:43,726 So, now, talk about collections for just a second. 1565 01:28:44,006 --> 01:28:46,436 The only ones we're going to see right now are these NSArray 1566 01:28:46,436 --> 01:28:52,896 and NSMutableArray where NSArray is in MutableArray 1567 01:28:53,306 --> 01:28:55,826 which pretty much means like one set exists. 1568 01:28:56,256 --> 01:28:56,976 It is what it is. 1569 01:28:56,976 --> 01:28:57,806 You can't change it. 1570 01:28:57,806 --> 01:29:00,446 MutableArray is going to be useful and that we're going 1571 01:29:00,446 --> 01:29:03,006 to be able to just keep adding things to it. 1572 01:29:03,646 --> 01:29:05,496 NSDictionary and NSMutableDictionary, 1573 01:29:05,496 --> 01:29:07,706 so those are going to be useful 1574 01:29:07,766 --> 01:29:13,366 for like KeyValuePair type stuff, associative arrays, maps, 1575 01:29:13,366 --> 01:29:15,076 whatever, hash tables, whatever you want to call them, 1576 01:29:15,076 --> 01:29:16,416 that's what you're going to use those for. 1577 01:29:16,946 --> 01:29:19,256 Set is just another example of the collection. 1578 01:29:19,546 --> 01:29:22,316 NSArray is going to be the most commonly used 1579 01:29:22,316 --> 01:29:24,136 and we're going to use it right here. 1580 01:29:24,136 --> 01:29:25,966 So, looking at the next example. 1581 01:29:26,516 --> 01:29:39,026 [ Pause ] 1582 01:29:39,526 --> 01:29:42,976 OK. So, Student.h and Student.m haven't changed. 1583 01:29:44,096 --> 01:29:47,536 It's main.m. Now, we're trying to do something interesting 1584 01:29:48,446 --> 01:29:53,176 where we have a NSMutableArray of students 1585 01:29:53,836 --> 01:29:56,386 and we're just allocate-- allocating it and initting it. 1586 01:29:56,896 --> 01:30:00,526 And then we want to insert into that array Alice and Bob. 1587 01:30:00,996 --> 01:30:02,806 So we've done it in one line. 1588 01:30:02,806 --> 01:30:04,426 If we wanted, we can do the same thing. 1589 01:30:04,426 --> 01:30:04,966 We can do-- 1590 01:30:05,516 --> 01:30:25,546 [ Pause ] 1591 01:30:26,046 --> 01:30:33,196 So, the NSMutableArray class defines an instance method 1592 01:30:33,326 --> 01:30:35,756 called AddObject that is just going 1593 01:30:35,756 --> 01:30:39,576 to take some argument with type ID. 1594 01:30:39,976 --> 01:30:42,396 And so since student star is an object type, 1595 01:30:42,636 --> 01:30:44,036 that isn't appropriate ID. 1596 01:30:45,426 --> 01:30:47,986 And then we're going to do that again with Bob. 1597 01:30:47,986 --> 01:30:50,906 So you name this as an array where the first element is Alice 1598 01:30:50,906 --> 01:30:52,096 and the second element is Bob. 1599 01:30:53,166 --> 01:30:57,536 And then here is I referenced this a while ago 1600 01:30:57,856 --> 01:31:02,326 that we have this for in syntax that we're able 1601 01:31:02,326 --> 01:31:04,076 to use with collections. 1602 01:31:04,876 --> 01:31:07,176 So this well also wok for dictionaries and sets. 1603 01:31:07,596 --> 01:31:12,736 So for each student in this NSMutableArray we want 1604 01:31:12,736 --> 01:31:14,256 to greet that student. 1605 01:31:15,036 --> 01:31:19,716 So one thing that's somewhat important to remember is 1606 01:31:19,716 --> 01:31:25,766 that everything inside of this array is just stored as an ID, 1607 01:31:26,186 --> 01:31:28,956 like there is nothing enforcing 1608 01:31:28,956 --> 01:31:31,246 that I only put students into this array. 1609 01:31:31,656 --> 01:31:36,226 If I wanted, I can put a student and then NSString 1610 01:31:36,226 --> 01:31:37,276 and then another student 1611 01:31:37,276 --> 01:31:41,016 and then some UITableViewController that's 1612 01:31:41,156 --> 01:31:45,686 it's up to you to enforce that everything is of the same type 1613 01:31:46,296 --> 01:31:47,166 or if you don't want to enforce 1614 01:31:47,166 --> 01:31:48,896 that you then just make sure it's makes sense. 1615 01:31:48,896 --> 01:31:54,066 You know what you're doing, but like if I wanted I could say, 1616 01:31:55,496 --> 01:31:59,936 this and this isn't going to work 1617 01:31:59,936 --> 01:32:05,696 because NSString doesn't have a name and age instance variable, 1618 01:32:05,996 --> 01:32:09,966 but it doesn't know what's inside of the students array. 1619 01:32:09,966 --> 01:32:12,746 So for all the compiler knows, it is an NSString. 1620 01:32:14,436 --> 01:32:17,136 This is where it can be somewhat dangerous dealing with ID 1621 01:32:17,676 --> 01:32:21,796 and this is also why you might need to be dealing with casts. 1622 01:32:22,126 --> 01:32:24,926 So, you might want some cast these return values 1623 01:32:24,926 --> 01:32:26,566 to the appropriate things. 1624 01:32:27,606 --> 01:32:31,536 Okay. So, questions on this iterating over an array? 1625 01:32:32,746 --> 01:32:32,976 Yeah. 1626 01:32:33,516 --> 01:32:35,576 [ Inaudible Remark ] 1627 01:32:36,076 --> 01:32:40,316 So it's-- how it's working underneath the hood is 1628 01:32:40,316 --> 01:32:44,216 that this NSMutableArray class needs 1629 01:32:44,216 --> 01:32:47,006 to define how to iterate over it. 1630 01:32:47,496 --> 01:32:51,236 And so in this method that it's defining for how to iterate 1631 01:32:51,236 --> 01:32:53,296 over it, it's saying that like, 1632 01:32:53,506 --> 01:32:55,836 "I'm going to do it in this order." 1633 01:32:55,836 --> 01:32:58,836 So it's saying that like index 0 is the first thing 1634 01:32:58,836 --> 01:33:00,956 that should be return then index 1 then index 2. 1635 01:33:00,956 --> 01:33:06,166 >> Is there any way for that to [inaudible] like- 1636 01:33:06,296 --> 01:33:14,186 >> So, we'll see-- I don't think there is to-- directly to erase. 1637 01:33:14,826 --> 01:33:18,926 We'll see though that protocols at the very least are ways 1638 01:33:18,926 --> 01:33:20,686 to make IDs a little stronger. 1639 01:33:21,446 --> 01:33:25,066 There are ways to make sure that these IDs are at least objects 1640 01:33:25,066 --> 01:33:26,966 that conform to a specific interface. 1641 01:33:27,806 --> 01:33:33,996 I don't think there's any generic type construct 1642 01:33:33,996 --> 01:33:34,636 in the language. 1643 01:33:35,516 --> 01:33:39,266 [ Pause ] 1644 01:33:39,766 --> 01:33:39,966 Okay. 1645 01:33:40,516 --> 01:33:47,076 [ Pause ] 1646 01:33:47,576 --> 01:33:49,566 Okay. So that's the syntax we just saw 1647 01:33:49,826 --> 01:33:54,376 and notice here we are saying for ID foo in bar 1648 01:33:54,746 --> 01:33:58,136 and so we don't know what is inside a bar 1649 01:33:58,136 --> 01:34:00,946 and so all we can really say is ID unless you happen 1650 01:34:00,946 --> 01:34:01,976 to know what it really is. 1651 01:34:02,516 --> 01:34:06,626 [ Pause ] 1652 01:34:07,126 --> 01:34:10,526 Okay. So, categories is a-- 1653 01:34:10,836 --> 01:34:12,686 actually, let's ignore that for a second 1654 01:34:12,686 --> 01:34:13,976 and let's do another example first. 1655 01:34:14,516 --> 01:34:16,936 [ Pause ] 1656 01:34:17,436 --> 01:34:18,736 Student 8. 1657 01:34:19,516 --> 01:34:26,676 [ Pause ] 1658 01:34:27,176 --> 01:34:31,346 Okay. So the point in this example is I've decided I don't 1659 01:34:31,346 --> 01:34:36,396 want to print these things in just whatever order I happen 1660 01:34:36,396 --> 01:34:37,836 to insert them into the array. 1661 01:34:37,956 --> 01:34:40,096 I first want to sort the array and then I want 1662 01:34:40,096 --> 01:34:41,226 to print out the sorted array. 1663 01:34:41,496 --> 01:34:45,686 So, there are couple of ways we can do that. 1664 01:34:45,686 --> 01:34:50,376 I inserted them in the order, RJ, Chris, Rob, David, and so, 1665 01:34:50,626 --> 01:34:52,116 here by looking 1666 01:34:52,116 --> 01:34:55,076 at the NSMutableArray documentation I see 1667 01:34:55,076 --> 01:34:58,096 that it has a whole bunch of different ways 1668 01:34:58,096 --> 01:34:59,306 of actually sorting things. 1669 01:35:00,416 --> 01:35:04,196 One way is this sorted array using selector method. 1670 01:35:04,276 --> 01:35:09,436 First, let's look at Student.h and Student.m. So, 1671 01:35:09,646 --> 01:35:10,916 inside of Student.h, 1672 01:35:10,976 --> 01:35:15,166 I have defined a new method called compare. 1673 01:35:15,996 --> 01:35:18,546 It's returning this NSComparisonResult, 1674 01:35:18,816 --> 01:35:21,526 and the only reason that's relevant is 1675 01:35:21,526 --> 01:35:27,936 because this sorted array using selector method expects a method 1676 01:35:27,936 --> 01:35:32,686 to be passed to it that returns an NSComparator result, 1677 01:35:32,686 --> 01:35:34,696 whatever it is. 1678 01:35:34,926 --> 01:35:39,486 So, this compare method is going to take another student 1679 01:35:39,966 --> 01:35:42,816 and just compare ourself, 1680 01:35:42,816 --> 01:35:44,666 our current student with that student. 1681 01:35:44,836 --> 01:35:47,306 Looking at the implementation of that, 1682 01:35:48,436 --> 01:35:51,106 I decided that I'm just going to compare it by name. 1683 01:35:51,516 --> 01:35:57,216 So, I'm going to use self.name references the NSString 1684 01:35:57,216 --> 01:36:00,446 that is my name and then I'm going to compare 1685 01:36:00,836 --> 01:36:03,776 that like the NSString compare method, I'm going to use 1686 01:36:03,776 --> 01:36:06,266 that to compare to the other students name. 1687 01:36:08,336 --> 01:36:12,496 And because this compare method returns an NSComparisonResults 1688 01:36:12,886 --> 01:36:14,106 that is an easy way of making sure 1689 01:36:14,106 --> 01:36:15,916 that I return an NSComparisonResult. 1690 01:36:17,126 --> 01:36:20,916 OK. So, now that I defined this method for students, 1691 01:36:21,516 --> 01:36:28,226 I'm now going to say here that I'm going 1692 01:36:28,226 --> 01:36:32,166 to sort the student's array using the selector compare. 1693 01:36:32,536 --> 01:36:36,586 So this special syntax @selector, remember that methods 1694 01:36:36,586 --> 01:36:39,956 and selectors are kind of like interchangeable words almost. 1695 01:36:40,406 --> 01:36:45,716 So, I can't just say like this 'cause that's not really a 1696 01:36:45,716 --> 01:36:46,936 valid syntax. 1697 01:36:47,146 --> 01:36:50,396 I want to say that I want to use the method compare colon, 1698 01:36:51,236 --> 01:36:55,856 and so to actually specify the method compare colon, 1699 01:36:56,066 --> 01:36:58,966 I wrap it in this special selector keyboard. 1700 01:36:59,466 --> 01:37:05,016 And so, what this sorted array using selector method is going 1701 01:37:05,016 --> 01:37:10,316 to do is iterate over the student's array calling the 1702 01:37:10,316 --> 01:37:13,796 compare method of each student to say like, OK, student 0 1703 01:37:13,796 --> 01:37:15,726 and student 1, how do you compare to each other? 1704 01:37:15,956 --> 01:37:18,256 And then like depending on how they compare is going 1705 01:37:18,256 --> 01:37:20,376 to determine whether student 0 belongs in front 1706 01:37:20,376 --> 01:37:22,566 of or after student 1. 1707 01:37:23,136 --> 01:37:26,086 So compare has to exist for everything 1708 01:37:26,086 --> 01:37:27,096 in this student's array. 1709 01:37:27,676 --> 01:37:30,556 And then let's just run it 1710 01:37:30,556 --> 01:37:33,076 to make sure that's the case that this works. 1711 01:37:33,876 --> 01:37:37,946 So we see a print Chris, David, RJ, Rob which is what we wanted. 1712 01:37:38,516 --> 01:37:47,876 [ Inaudible Remark ] 1713 01:37:48,376 --> 01:37:51,446 >> So how do you in here-- 1714 01:37:51,886 --> 01:37:57,996 and you can also decide that we just want to compare ages. 1715 01:37:58,746 --> 01:38:03,656 This isn't quite right because they're ints and I'm not sure 1716 01:38:03,656 --> 01:38:05,316 of what NSComparison looks like. 1717 01:38:06,136 --> 01:38:12,506 It might just be like return Self.age less 1718 01:38:12,506 --> 01:38:14,566 than other Student.age, or I guess maybe 1719 01:38:14,566 --> 01:38:16,996 like if 1 is less than, I'm supposed to return 1. 1720 01:38:17,196 --> 01:38:20,356 Or if they're equal, I return 0 or else negative 1. 1721 01:38:20,666 --> 01:38:22,966 I'm not sure what NSComparison, what it was supposed 1722 01:38:22,966 --> 01:38:24,576 to look like actually. 1723 01:38:25,266 --> 01:38:30,486 So, another-- let's go to here again. 1724 01:38:30,796 --> 01:38:35,426 So, a useful syntax that we've already seen this useful 1725 01:38:35,426 --> 01:38:37,996 shorthand for defining an NSString, that's blah, blah, 1726 01:38:37,996 --> 01:38:40,226 blah with the @ sign in front of double quotes. 1727 01:38:40,866 --> 01:38:44,336 Another useful syntax is an @ sign in front of brackets 1728 01:38:44,626 --> 01:38:52,576 for shorthand for defining arrays, so and NSArrays. 1729 01:38:54,696 --> 01:38:59,246 So now I've defined an array, an NS array with two objects, 1730 01:38:59,546 --> 01:39:01,376 Hello and World, two NSStrings. 1731 01:39:02,406 --> 01:39:06,356 And additional shorthand that's somewhat is @ 1732 01:39:06,596 --> 01:39:08,016 in front of any number. 1733 01:39:08,186 --> 01:39:12,906 So this defines the approach like NSString was the first one, 1734 01:39:12,906 --> 01:39:13,986 NSArray was the second one. 1735 01:39:14,196 --> 01:39:17,356 This defines an NSNumber with the value 42. 1736 01:39:18,226 --> 01:39:20,276 And so, what may or may not work. 1737 01:39:20,476 --> 01:39:21,566 What I'm going to show it right here. 1738 01:39:21,796 --> 01:39:25,766 No, actually that won't work at all. 1739 01:39:25,886 --> 01:39:32,086 So, I might be able to do init NSNumber alloc. 1740 01:39:32,276 --> 01:39:41,076 I just want to save the sense of working at this point, 1741 01:39:41,076 --> 01:39:45,656 init with int self.age. 1742 01:39:46,116 --> 01:39:57,046 And then I want to compare that, now I have a compare method. 1743 01:39:57,866 --> 01:40:03,656 Compare to another NSNumber should be NSNumber alloc init 1744 01:40:04,086 --> 01:40:08,796 with int, other student, age. 1745 01:40:09,516 --> 01:40:13,136 [ Pause ] 1746 01:40:13,636 --> 01:40:17,266 OK. So questions on what I just did there. 1747 01:40:17,586 --> 01:40:17,946 Yes. 1748 01:40:18,056 --> 01:40:20,116 >> You didn't use the selector up here. 1749 01:40:20,706 --> 01:40:22,326 >> So, I'm not using-- here, 1750 01:40:22,326 --> 01:40:24,186 I'm just defining the compare method. 1751 01:40:25,546 --> 01:40:28,506 It's when I want to actually reference the compare method 1752 01:40:28,766 --> 01:40:34,536 that in here I say the method I want to use is compare calling. 1753 01:40:34,536 --> 01:40:36,656 And this is again like I said before, like the literal name 1754 01:40:36,656 --> 01:40:38,126 of the thing includes the colon. 1755 01:40:38,506 --> 01:40:41,036 So here I'm referencing the method compare colon 1756 01:40:41,506 --> 01:40:43,956 and the definition of it, I don't need to use @selector. 1757 01:40:45,516 --> 01:40:50,436 [ Inaudible Remark ] 1758 01:40:50,936 --> 01:40:52,686 A method to a method, yeah. 1759 01:40:54,006 --> 01:40:55,856 'Cause if it were a function, 1760 01:40:55,856 --> 01:40:57,186 I wouldn't need to use that selector. 1761 01:40:57,186 --> 01:40:59,896 I could literally just use a function pointer 1762 01:40:59,896 --> 01:41:01,436 but you don't need to deal with those here. 1763 01:41:01,966 --> 01:41:08,436 There is some-- there is probably some spacing 1764 01:41:08,436 --> 01:41:08,996 error here. 1765 01:41:08,996 --> 01:41:15,706 All right, 'cause I don't need this, whatever. 1766 01:41:16,186 --> 01:41:18,896 That's the general idea. 1767 01:41:19,746 --> 01:41:23,266 So, that's that. 1768 01:41:24,236 --> 01:41:26,926 Questions before I move on to a similar idea? 1769 01:41:27,066 --> 01:41:27,186 Yeah. 1770 01:41:28,516 --> 01:41:35,106 [ Inaudible Question ] 1771 01:41:35,606 --> 01:41:39,116 >> And just as-- remember, it's like C where-- 1772 01:41:40,336 --> 01:41:45,246 it's like C where this, in order to get the prototype 1773 01:41:45,246 --> 01:41:49,466 for this thing, I can literally just like copy this, paste it, 1774 01:41:49,466 --> 01:41:50,786 put a semicolon at the end. 1775 01:41:51,546 --> 01:41:53,446 So the prototype is just the first line 1776 01:41:53,446 --> 01:41:59,496 of your definition of the function. 1777 01:41:59,496 --> 01:42:03,686 OK. So, that's that and now we're going 1778 01:42:03,686 --> 01:42:06,996 to students 9 'cause we're getting into categories 1779 01:42:07,596 --> 01:42:21,236 which that's not very helpful so here, let's-- OK. 1780 01:42:21,236 --> 01:42:25,256 So, the idea behind categories is notice that in order 1781 01:42:25,256 --> 01:42:26,986 to do what I just did, I needed 1782 01:42:26,986 --> 01:42:31,736 to actively modify the student class which is fine 1783 01:42:31,736 --> 01:42:35,566 because I'm the one who created the student class so it's fine 1784 01:42:35,566 --> 01:42:37,936 for me to go into the student class and add a compare method. 1785 01:42:38,906 --> 01:42:41,046 But, what if this class that I need 1786 01:42:41,046 --> 01:42:43,326 to modify is not something I have access to? 1787 01:42:43,606 --> 01:42:47,946 What if it's in some compiled library or it's one of the-- 1788 01:42:47,976 --> 01:42:50,246 one of the foundation classes or an iOS class. 1789 01:42:50,816 --> 01:42:52,516 I need to add a method to it 1790 01:42:53,016 --> 01:42:55,156 but I don't have access to the source code. 1791 01:42:55,756 --> 01:42:56,966 So these are what categories are 1792 01:42:57,066 --> 01:42:59,956 for therefore extending existing classes. 1793 01:43:00,696 --> 01:43:04,796 And so, in Xcode you can actually do this like file new, 1794 01:43:05,266 --> 01:43:08,006 file and then Category and then 1795 01:43:08,006 --> 01:43:09,346 like walkthrough through the steps. 1796 01:43:09,836 --> 01:43:13,416 And the default format of these categories, so remember, 1797 01:43:13,416 --> 01:43:14,526 I'm working under the assumption 1798 01:43:14,526 --> 01:43:16,306 that I don't have access to the student class. 1799 01:43:17,046 --> 01:43:24,526 So the default format of these filenames are student 1800 01:43:24,786 --> 01:43:27,736 which is the class that I'm extending, plus, 1801 01:43:27,836 --> 01:43:29,976 and what I happen to call the category. 1802 01:43:30,586 --> 01:43:35,356 So here, I am extending the student class 1803 01:43:35,726 --> 01:43:39,766 with the category StudentCompare and this is just the syntax 1804 01:43:39,766 --> 01:43:42,906 that you're free to look out whenever you happen to need 1805 01:43:42,906 --> 01:43:44,166 to extend a class like this. 1806 01:43:44,986 --> 01:43:51,396 So, this extension of the student class is going 1807 01:43:51,396 --> 01:43:53,116 to include this method. 1808 01:43:53,646 --> 01:43:58,506 A category is not able to define instance variables, 1809 01:43:58,656 --> 01:44:02,066 it's only able to define new methods for a class. 1810 01:44:02,306 --> 01:44:05,886 So, looking at the implementation of this category, 1811 01:44:06,526 --> 01:44:10,336 again, it's-- the category itself is StudentCompare 1812 01:44:10,586 --> 01:44:12,286 and I am extending student 1813 01:44:12,596 --> 01:44:15,536 and I'm implementing it basically how I implemented it 1814 01:44:15,536 --> 01:44:18,506 before, exactly the same, except I'm able to do this 1815 01:44:18,506 --> 01:44:21,196 without ever touching the original Student.h 1816 01:44:21,196 --> 01:44:25,726 and Student.m. And this will work exactly the same. 1817 01:44:25,726 --> 01:44:28,626 Now, in main.m, inside of importing Student.h, 1818 01:44:28,626 --> 01:44:31,316 I import Student+StudentCompare.h. The 1819 01:44:31,316 --> 01:44:34,476 StudentCompare.h is what is importing Student.h. 1820 01:44:35,106 --> 01:44:41,236 And everything else in here is the same. 1821 01:44:41,466 --> 01:44:41,916 Yes. 1822 01:44:42,516 --> 01:44:52,136 [ Inaudible Remark ] 1823 01:44:52,636 --> 01:44:53,976 >> Oh name, OK. 1824 01:44:54,271 --> 01:44:56,271 [ Inaudible Remark ] 1825 01:44:56,526 --> 01:44:59,846 >> Oh these angled brackets and quotes. 1826 01:45:00,306 --> 01:45:06,886 So the angled brackets refer to like these special directories 1827 01:45:06,966 --> 01:45:09,166 in the file system, in the operating system that it knows 1828 01:45:09,166 --> 01:45:11,856 to look in to find these files. 1829 01:45:11,946 --> 01:45:15,306 So like Foundation/Foundation.h is in one 1830 01:45:15,306 --> 01:45:16,446 such special directory. 1831 01:45:16,816 --> 01:45:20,586 Whereas these double quotes are what you're going to want to use 1832 01:45:20,586 --> 01:45:22,716 to refer to files in your current project. 1833 01:45:23,346 --> 01:45:27,976 So, in this project, I have a Student+StudentCompare.h file. 1834 01:45:28,496 --> 01:45:30,176 Double quotes is like relative 1835 01:45:30,176 --> 01:45:33,566 to my current location whereas angled brackets automatically 1836 01:45:33,566 --> 01:45:34,986 goes to these special directories. 1837 01:45:35,886 --> 01:45:35,976 Yeah? 1838 01:45:36,516 --> 01:45:56,756 [ Inaudible Remark ] 1839 01:45:57,256 --> 01:45:59,806 You mean by addendum, do you mean like this sort 1840 01:45:59,806 --> 01:46:00,976 of stuff, this category stuff? 1841 01:46:01,016 --> 01:46:02,076 [Inaudible Remark ] 1842 01:46:02,076 --> 01:46:03,066 Oh, then yes. 1843 01:46:03,066 --> 01:46:05,836 So, in student Compare.h, well, 1844 01:46:06,026 --> 01:46:08,406 let's say Student.h was a foundation class. 1845 01:46:08,406 --> 01:46:08,686 >> Yeah, yeah. 1846 01:46:08,686 --> 01:46:11,906 >> Then I would do foundation/Student.h. 1847 01:46:12,396 --> 01:46:15,976 And inside its main, I would still do the 1848 01:46:15,976 --> 01:46:19,286 Student+StudentCompare.h. I wouldn't import the original 1849 01:46:19,286 --> 01:46:20,506 foundation version of things. 1850 01:46:20,506 --> 01:46:22,166 I would import my version of things 1851 01:46:22,166 --> 01:46:22,976 that have been overwritten. 1852 01:46:23,516 --> 01:46:32,146 [ Inaudible Remark ] 1853 01:46:32,646 --> 01:46:36,946 Yes, it's actually just an extension. 1854 01:46:36,946 --> 01:46:41,206 It's the-- it is the same class. 1855 01:46:41,546 --> 01:46:43,496 And anywhere else in your code that uses 1856 01:46:43,496 --> 01:46:46,146 that class could also use that new method. 1857 01:46:47,466 --> 01:46:49,446 If it doesn't happen to hush import, 1858 01:46:49,446 --> 01:46:52,196 the correct category file, the compiler will complain 1859 01:46:52,196 --> 01:46:54,506 that like it doesn't know that method exists. 1860 01:46:55,056 --> 01:46:59,486 But that method now actually exists for that class. 1861 01:47:00,016 --> 01:47:02,016 [ Pause ] 1862 01:47:02,016 --> 01:47:03,000 [ Inaudible Remark ] 1863 01:47:03,256 --> 01:47:04,046 >> Mm-hmm. 1864 01:47:04,046 --> 01:47:07,296 >> Where is NSComparisonResult coming from, is that a library? 1865 01:47:07,406 --> 01:47:10,456 >> So, that's something in Foundation/Foundation.h, 1866 01:47:10,836 --> 01:47:14,456 we could actually just look it up, NSComparisonResult. 1867 01:47:14,456 --> 01:47:21,456 So, something about the Apple documentation is 1868 01:47:21,456 --> 01:47:23,596 that it can be overwhelming. 1869 01:47:23,796 --> 01:47:27,066 But it has a lot of good examples so feel free 1870 01:47:27,066 --> 01:47:28,766 to ask questions on like the message board if it-- 1871 01:47:28,766 --> 01:47:30,616 you just find yourself lost in a path 1872 01:47:30,616 --> 01:47:32,806 of various methods and stuff. 1873 01:47:33,526 --> 01:47:39,866 So, data types, what was I was looking, NSComparison. 1874 01:47:40,376 --> 01:47:46,326 So, it looks like NSComparisonResult is-- 1875 01:47:46,666 --> 01:47:48,316 all right, this syntax, you don't even know yet. 1876 01:47:48,596 --> 01:47:50,126 Let's hold on for that. 1877 01:47:50,676 --> 01:47:52,446 That's going to be the next thing. 1878 01:47:52,976 --> 01:47:56,166 But NSComparisonResult is just something 1879 01:47:56,166 --> 01:47:59,036 that foundation defines. 1880 01:47:59,036 --> 01:48:02,126 And that's why I wasn't 100 percent sure what it is. 1881 01:48:02,346 --> 01:48:06,016 I just know that the compare methods of NSString 1882 01:48:06,016 --> 01:48:10,106 and NSNumber also a different return NSComparisonResults 1883 01:48:10,296 --> 01:48:11,216 and so that's what I use. 1884 01:48:11,826 --> 01:48:15,986 But if you wanted, you can construct your own 1885 01:48:16,106 --> 01:48:20,016 NSComparisonResult to return. 1886 01:48:20,016 --> 01:48:25,226 OK. Questions for the next thing? 1887 01:48:25,386 --> 01:48:31,646 So, next thing is this. 1888 01:48:31,646 --> 01:48:33,146 Again, I think slide is going to be worthless. 1889 01:48:34,566 --> 01:48:38,526 So blocks, so that's the general format of blocks, 1890 01:48:38,526 --> 01:48:39,826 but that's worthless so-- 1891 01:48:40,676 --> 01:48:42,386 looking at the example of using a block. 1892 01:48:43,516 --> 01:48:56,036 [ Pause ] 1893 01:48:56,536 --> 01:48:59,406 OK. So, back to Student.h and Student.m, 1894 01:49:00,146 --> 01:49:02,276 I have not modified them to include the compare method. 1895 01:49:02,996 --> 01:49:07,276 I have not added a category to extend the class. 1896 01:49:08,596 --> 01:49:11,286 Instead, I've used what's called a block. 1897 01:49:11,686 --> 01:49:14,956 So a block is kind of like an anonymous function 1898 01:49:14,956 --> 01:49:15,986 in other languages. 1899 01:49:15,986 --> 01:49:20,346 It's-- it doesn't even have to be anonymous. 1900 01:49:20,346 --> 01:49:22,136 If you wanted, you could assign it to a variable. 1901 01:49:22,336 --> 01:49:25,366 It's kind of like, if you're familiar with the term, 1902 01:49:25,366 --> 01:49:29,846 it's like giving objective-C first class functions to like 1903 01:49:30,356 --> 01:49:33,326 in objective-C, I'm not really able to just define a function 1904 01:49:33,326 --> 01:49:35,016 in the middle of this method. 1905 01:49:35,016 --> 01:49:38,136 That's not entirely valid, whereas, 1906 01:49:38,136 --> 01:49:39,716 I am able to define a block. 1907 01:49:40,296 --> 01:49:44,326 So, just like in JavaScript, you saw a syntax like this. 1908 01:49:44,696 --> 01:49:48,616 Here, we have-- we are using a different method. 1909 01:49:49,076 --> 01:49:52,296 So, before, we use sorted array using selector. 1910 01:49:52,736 --> 01:49:54,886 Now, we're doing sorted array using comparator. 1911 01:49:55,366 --> 01:49:58,346 And so, this comparator expects a block 1912 01:49:59,286 --> 01:50:02,186 that this little caret symbol specifies 1913 01:50:02,236 --> 01:50:04,646 that what is following this is a block. 1914 01:50:06,056 --> 01:50:10,046 And this is the return type of the block, NSComparisonResult. 1915 01:50:11,046 --> 01:50:16,576 This is the two-- now this is the type of the first argument 1916 01:50:16,576 --> 01:50:17,776 and this is the type of second argument. 1917 01:50:17,916 --> 01:50:20,056 And I know this because if I look at the documentation 1918 01:50:20,056 --> 01:50:21,856 for sorted array using comparator, 1919 01:50:22,256 --> 01:50:24,346 its argument is supposed to be a block 1920 01:50:24,686 --> 01:50:26,526 that returns an NSComparisonResult 1921 01:50:26,716 --> 01:50:28,646 and takes two arguments that are both IDs. 1922 01:50:29,276 --> 01:50:32,186 So this, I got directly from the documentation. 1923 01:50:33,266 --> 01:50:35,856 And then I need to define the function itself 1924 01:50:35,856 --> 01:50:37,696 so I have my little curly brace. 1925 01:50:38,326 --> 01:50:44,026 And in here, I'm doing the same sort of thing I did before. 1926 01:50:44,026 --> 01:50:48,686 We see here that I cast A to student star and that's 1927 01:50:48,686 --> 01:50:52,216 because in here, A is just an ID, in here, B is just an ID. 1928 01:50:52,606 --> 01:50:55,606 So if I actually want it to be a student object, I first need 1929 01:50:55,606 --> 01:50:57,856 to cast it before or passing it a name. 1930 01:50:58,806 --> 01:51:01,746 So Student star A name, Student star B name, 1931 01:51:01,746 --> 01:51:02,696 gives me these two names 1932 01:51:02,696 --> 01:51:04,866 and then I use the NSString's compare method. 1933 01:51:05,146 --> 01:51:08,366 So I don't have to construct my own NSComparisonResult. 1934 01:51:09,986 --> 01:51:12,436 And we know that this appropriately returns an 1935 01:51:12,466 --> 01:51:14,426 NSComparisonResult like this at it should. 1936 01:51:15,886 --> 01:51:18,616 So blocks anonymous functions. 1937 01:51:18,856 --> 01:51:22,096 The syntax is a little strange but it's convenient 1938 01:51:22,096 --> 01:51:24,766 that like I don't need to define a method 1939 01:51:24,766 --> 01:51:28,556 in the student class just to sort this array, 1940 01:51:29,466 --> 01:51:32,726 which like that was a very heavy-handed result just 1941 01:51:32,726 --> 01:51:33,616 to get a sorted array. 1942 01:51:36,576 --> 01:51:36,776 [Inaudible Remark] Yes. 1943 01:51:37,076 --> 01:51:43,336 So that's where-- I don't remember the syntax. 1944 01:51:43,336 --> 01:51:47,196 But it's going to look something like-- so-- 1945 01:51:48,516 --> 01:51:51,266 [ Pause ] 1946 01:51:51,766 --> 01:51:56,646 It's something like what it returns, 1947 01:51:57,016 --> 01:52:03,986 then in parentheses what I want to call it, then ID, ID equals. 1948 01:52:03,986 --> 01:52:06,786 And then pass it-- 1949 01:52:07,516 --> 01:52:10,216 [ Pause ] 1950 01:52:10,716 --> 01:52:11,686 -- to here. 1951 01:52:14,996 --> 01:52:15,596 Didn't complain. 1952 01:52:16,576 --> 01:52:19,566 [laughs] So, if you're familiar with function pointers in C, 1953 01:52:19,716 --> 01:52:21,256 I just sort of used that same syntax. 1954 01:52:21,256 --> 01:52:25,916 I replaced the star with a caret. 1955 01:52:26,336 --> 01:52:32,376 So, here is, we are defining a variable called func 1956 01:52:33,656 --> 01:52:36,786 that is a block as indicated by this caret. 1957 01:52:38,066 --> 01:52:40,366 This is-- the return type 1958 01:52:40,366 --> 01:52:42,326 of that block is NSComparisonResult. 1959 01:52:42,636 --> 01:52:43,846 The arguments are two IDs. 1960 01:52:43,846 --> 01:52:46,756 And you're assigning that to this block. 1961 01:52:47,456 --> 01:52:48,936 And then we're passing that variable 1962 01:52:49,016 --> 01:52:52,106 to that function, to that method. 1963 01:52:53,516 --> 01:52:57,836 [ Pause ] 1964 01:52:58,336 --> 01:52:58,666 Questions? 1965 01:52:59,516 --> 01:53:02,866 [ Pause ] 1966 01:53:03,366 --> 01:53:03,566 OK. 1967 01:53:04,516 --> 01:53:09,186 [ Pause ] 1968 01:53:09,686 --> 01:53:11,506 So couple last things. 1969 01:53:12,516 --> 01:53:20,186 [ Pause ] 1970 01:53:20,686 --> 01:53:22,116 OK, so protocols. 1971 01:53:22,116 --> 01:53:25,996 We're not going to go into deep detail today about them. 1972 01:53:26,386 --> 01:53:31,686 But they are going to be pretty substantial in your iOS usage. 1973 01:53:32,256 --> 01:53:37,806 So the syntax for this, remember that well, in our interface, 1974 01:53:37,806 --> 01:53:39,496 we would also say like :NSObject. 1975 01:53:39,696 --> 01:53:42,966 But here, this angle bracket syntax is how we're going 1976 01:53:42,966 --> 01:53:46,156 to specify that it must adhere to some protocol. 1977 01:53:46,846 --> 01:53:48,816 And so the NSCopying Protocol, 1978 01:53:49,126 --> 01:53:51,526 this is where I'm saying the protocol is kind of interfaces 1979 01:53:51,526 --> 01:53:53,346 from other languages by saying 1980 01:53:53,346 --> 01:53:55,776 that the student interface implements the 1981 01:53:55,776 --> 01:53:56,926 NSCopying Protocol. 1982 01:53:57,226 --> 01:53:59,416 I'm saying that it must implement the methods 1983 01:53:59,416 --> 01:54:02,246 that NSCopying says, anything 1984 01:54:02,246 --> 01:54:03,796 that implements me must implement. 1985 01:54:05,066 --> 01:54:07,336 So, looking at the implementation now, 1986 01:54:09,116 --> 01:54:13,906 if we look at NSCopying, it says that you must implement a copy 1987 01:54:13,906 --> 01:54:15,876 with zone function method. 1988 01:54:16,426 --> 01:54:18,016 And so here's us implementing it. 1989 01:54:18,016 --> 01:54:20,606 You don't really have to care about the syntax of it for now 1990 01:54:20,606 --> 01:54:22,096 or the-- what it actually is doing. 1991 01:54:22,486 --> 01:54:26,096 Just the idea that since student implements the NSCopying 1992 01:54:26,096 --> 01:54:29,286 Protocol, it must implement all the function, 1993 01:54:29,386 --> 01:54:31,336 all the methods that NSCopying says. 1994 01:54:31,896 --> 01:54:40,766 And the use of this as we see is going to be like a lot 1995 01:54:40,766 --> 01:54:42,226 of these functions that-- 1996 01:54:42,226 --> 01:54:45,546 or a lot of like classes that you're going to be using 1997 01:54:45,546 --> 01:54:48,266 with iOS, like a lot of these drawing classes, 1998 01:54:48,666 --> 01:54:50,986 are going to expect you to pass it objects 1999 01:54:51,186 --> 01:54:52,856 that must adhere to certain protocols. 2000 01:54:53,466 --> 01:54:56,566 For example, UITableView is one. 2001 01:54:56,836 --> 01:54:58,766 Let's actually looked at documentation, 2002 01:55:00,266 --> 01:55:01,946 this documentation work. 2003 01:55:02,516 --> 01:55:13,056 [ Pause ] 2004 01:55:13,556 --> 01:55:16,766 OK. So we see in the documentation 2005 01:55:17,046 --> 01:55:20,056 that it looks like a data source. 2006 01:55:20,126 --> 01:55:25,006 So, UITableView is, in like your iPhone, 2007 01:55:25,006 --> 01:55:27,096 it would be like your contact list sort of, 2008 01:55:27,096 --> 01:55:29,786 it's just like a bunch of rows with data in them 2009 01:55:29,786 --> 01:55:31,046 and you can scroll up and down on it. 2010 01:55:31,676 --> 01:55:37,796 So here, UITableView defines a data source property 2011 01:55:38,426 --> 01:55:41,826 where the type of that data source is just an ID 2012 01:55:42,176 --> 01:55:44,586 that implements UITableView data source. 2013 01:55:45,496 --> 01:55:49,466 And so this is important because if you then set this property 2014 01:55:49,466 --> 01:55:52,206 to be some object, that means 2015 01:55:52,206 --> 01:55:55,126 that that object must implement this protocol, 2016 01:55:55,656 --> 01:55:59,106 what this protocol says must be implemented are-- 2017 01:55:59,696 --> 01:56:02,036 so some methods are optional, some are required, 2018 01:56:02,196 --> 01:56:03,746 so these two methods are required. 2019 01:56:04,226 --> 01:56:08,026 And so, when you set that property of a UITableView 2020 01:56:08,026 --> 01:56:11,786 with some object, that object must have these two methods. 2021 01:56:12,096 --> 01:56:16,916 Let's say, like how many rows there should be in this table, 2022 01:56:17,196 --> 01:56:19,746 in this section, and also what should go 2023 01:56:19,746 --> 01:56:20,906 in each particular cell. 2024 01:56:21,726 --> 01:56:24,676 So when you try to create a TableView, 2025 01:56:24,676 --> 01:56:28,166 you need to pass some object that is capable 2026 01:56:28,166 --> 01:56:30,586 of populating the cells of that TableView. 2027 01:56:31,136 --> 01:56:37,476 And so, UITableView knows that you are capable of doing 2028 01:56:37,476 --> 01:56:42,096 that if you implement the protocol. 2029 01:56:42,416 --> 01:56:44,556 And you'll see that that sort of pattern is going 2030 01:56:44,556 --> 01:56:46,296 to be pretty common with a lot of things you do. 2031 01:56:49,716 --> 01:56:50,976 Questions with protocols? 2032 01:56:51,516 --> 01:56:55,476 [ Pause ] 2033 01:56:55,976 --> 01:56:57,146 And that's really why I like it. 2034 01:56:57,146 --> 01:56:58,986 You compare to like a Java interface. 2035 01:56:59,276 --> 01:57:01,006 Protocols are much more similar to those 2036 01:57:01,006 --> 01:57:05,516 since like protocols almost define a new type kind of, 2037 01:57:05,856 --> 01:57:10,036 whereas like an interface in Objective-C is just a list 2038 01:57:10,036 --> 01:57:11,566 of all the methods that you implement. 2039 01:57:12,116 --> 01:57:13,576 It doesn't say anything intelligent 2040 01:57:13,576 --> 01:57:19,216 about like, "OK, you're welcome." 2041 01:57:19,456 --> 01:57:23,696 Really, what protocols allow are like multiple objects to all-- 2042 01:57:23,696 --> 01:57:27,646 multiple classes to all fulfill some common purpose. 2043 01:57:28,116 --> 01:57:31,766 So as long as like-- an example are all these 2044 01:57:31,766 --> 01:57:35,006 like enumeration classes, the collection classes, NSArray, 2045 01:57:35,006 --> 01:57:36,656 and NSDictionary, and all those, 2046 01:57:37,136 --> 01:57:39,936 as long as you appropriately implement some protocol, 2047 01:57:40,176 --> 01:57:43,106 then you are able to use the fast enumeration syntax 2048 01:57:43,176 --> 01:57:46,846 on that object, that for...in syntax. 2049 01:57:47,376 --> 01:57:52,046 And, again, much more than that. 2050 01:57:52,046 --> 01:57:53,856 All right. 2051 01:57:53,856 --> 01:57:55,846 Just-- so you've seen it. 2052 01:57:56,436 --> 01:57:59,716 NSExceptions is very similar to some other languages, the try 2053 01:57:59,716 --> 01:58:02,166 and catch blocks and we also happen to have finally. 2054 01:58:02,606 --> 01:58:07,656 So that's just to know it exists. 2055 01:58:09,146 --> 01:58:11,256 You probably won't even use them that much, 2056 01:58:11,446 --> 01:58:15,216 but that's useful to know. 2057 01:58:15,336 --> 01:58:17,326 NSError is somewhat of an alternative. 2058 01:58:17,326 --> 01:58:19,936 So, instead of having to use 2059 01:58:19,936 --> 01:58:23,676 like the try-catch-finally syntax can be somewhat large, 2060 01:58:23,676 --> 01:58:27,236 especially if like each one of those do something here, 2061 01:58:27,236 --> 01:58:31,696 just like a single line then you've sort of like wrapped it 2062 01:58:31,696 --> 01:58:34,966 with three times as many lines are accomplishing something. 2063 01:58:35,856 --> 01:58:39,486 So, NS-- or well, this sort of syntax, 2064 01:58:40,056 --> 01:58:41,726 this is one of the rare scenarios 2065 01:58:41,726 --> 01:58:45,296 where are you are going to be using ampersand still, so-- 2066 01:58:45,346 --> 01:58:47,666 again, we're never dereferencing an object, 2067 01:58:48,606 --> 01:58:52,636 but we are passing the address of an object. 2068 01:58:53,306 --> 01:58:56,916 We are passing the address of this NSError so that 2069 01:58:56,986 --> 01:59:01,476 if something happens to go wrong when we pass the method bar-- 2070 01:59:01,716 --> 01:59:03,296 the method is called bar:error:. 2071 01:59:03,296 --> 01:59:07,366 So when we pass the method bar:error: foo, 2072 01:59:08,036 --> 01:59:09,836 if something happens to go wrong, 2073 01:59:10,246 --> 01:59:16,856 then foo will instantiate an NSError object and set E 2074 01:59:17,066 --> 01:59:18,546 to be that NSError object. 2075 01:59:19,126 --> 01:59:23,326 So, inside of here, if something went wrong, E will not be nil. 2076 01:59:24,246 --> 01:59:29,776 If we just pass E, then inside of this function, this method, 2077 01:59:29,776 --> 01:59:31,616 it would have to dereference E 2078 01:59:31,696 --> 01:59:32,846 which is something you shouldn't be doing. 2079 01:59:32,846 --> 01:59:34,926 You should never dereference an object. 2080 01:59:35,896 --> 01:59:38,796 Plus, if you try to dereference E, you'd be dereferencing nil. 2081 01:59:40,516 --> 01:59:46,276 [ Inaudible Remark ] 2082 01:59:46,776 --> 01:59:50,846 So it will-- by returning nil, it's indicating 2083 01:59:50,846 --> 01:59:54,126 that something went wrong and then inside of here, now, 2084 01:59:54,126 --> 01:59:56,936 since something must have gone wrong, E must be set 2085 01:59:56,936 --> 01:59:57,926 to something that isn't nil. 2086 01:59:58,296 --> 02:00:01,376 Inside of the function, it must have instantiated an NSError 2087 02:00:01,376 --> 02:00:07,746 object and did like star-- star E equals this NSError object. 2088 02:00:08,516 --> 02:00:19,436 [ Inaudible Remark ] 2089 02:00:19,936 --> 02:00:21,816 Well, it's-- well, the function 2090 02:00:21,816 --> 02:00:24,396 or the method is bar error, bar:error:. 2091 02:00:25,066 --> 02:00:26,616 But if something goes wrong, yeah. 2092 02:00:26,616 --> 02:00:28,776 It-- that's just like when you read the documentation, 2093 02:00:28,776 --> 02:00:32,166 it will say like, "If something goes wrong, nil will be returned 2094 02:00:32,166 --> 02:00:34,866 and error will be set to some NSError." 2095 02:00:35,496 --> 02:00:40,446 So, it's also possible that it will return void and then it's 2096 02:00:40,446 --> 02:00:42,956 up to you just to see if E is still nil 2097 02:00:43,136 --> 02:00:44,526 and that's the way you know there was an error. 2098 02:00:45,296 --> 02:00:49,296 But, that's just-- in this example, we say, nil is returned 2099 02:00:49,296 --> 02:00:52,866 on error and what that error was is inside 2100 02:00:53,946 --> 02:00:57,176 of E. [Inaudible Remark] Yeah, it's not. 2101 02:00:57,336 --> 02:01:01,236 So, instead of just failing, we just put it inside of E. 2102 02:01:04,196 --> 02:01:06,496 But other things do use the try-catch syntax 2103 02:01:06,916 --> 02:01:09,086 so some things don't have this. 2104 02:01:10,916 --> 02:01:12,496 All right. 2105 02:01:13,386 --> 02:01:13,976 Any other questions? 2106 02:01:14,516 --> 02:01:17,276 [ Pause ] 2107 02:01:17,776 --> 02:01:20,626 I think that's it for our Objective-C intro. 2108 02:01:20,986 --> 02:01:25,346 If there is anything left, it was a lot, 2109 02:01:25,346 --> 02:01:30,226 but we haven't really done any iOS stuff so we'll throw all 2110 02:01:30,226 --> 02:01:30,986 that at you next week.