Friday Session 1. Debugging and Xcode Tips and Tricks.srt

1
00:00:00,267 --> 00:00:04,603
[MUSIC]                         

2
00:00:04,672 --> 00:00:07,372
Stanford University.            

3
00:00:07,441 --> 00:00:08,940
>> Alrighty, well,              
hi everybody.                   

4
00:00:09,009 --> 00:00:11,176
My name is Jason.               
I'm one of your two TAs.        

5
00:00:11,178 --> 00:00:13,412
Junjie is the other one.        
She is not here today and       

6
00:00:13,414 --> 00:00:13,445
we are gonna go over today      
kinda two different things.     

7
00:00:14,515 --> 00:00:17,249
we are gonna go over today      
kinda two different things.     

8
00:00:17,317 --> 00:00:19,818
One is just a whirlwind tour    
of Xcode just to make your      

9
00:00:19,886 --> 00:00:21,353
life a lot simpler for          
the entire quarter and          

10
00:00:21,421 --> 00:00:23,856
the rest of your life to make   
it more familiar to you.        

11
00:00:23,924 --> 00:00:26,391
And the other thing is how to   
use the debugger within Xcode   

12
00:00:26,460 --> 00:00:27,426
in particular.                  

13
00:00:29,830 --> 00:00:31,830
than most sections just cuz     
there's not that much material  

14
00:00:31,899 --> 00:00:33,965
to get through, so we'll        
be out of here a bit early.     

15
00:00:34,034 --> 00:00:35,867
But um, there is also,          
there is also no slides or      

16
00:00:35,936 --> 00:00:37,803
anything like that,             
there is no lecture to give,    

17
00:00:37,871 --> 00:00:39,871
it's just I'm gonna hop         
right into the demo.            

18
00:00:39,940 --> 00:00:42,107
And feel free to stop me        
at any point, just shout,       

19
00:00:42,175 --> 00:00:44,009
raise your hand if something    
is not clear if you wanna,      

20
00:00:44,078 --> 00:00:46,110
you wanna learn more about      
something or whatever, and      

21
00:00:46,179 --> 00:00:47,412
I'll stop to do that.           

22
00:00:47,481 --> 00:00:49,414
I know we're going through      
a giant list of key commands.   

23
00:00:49,483 --> 00:00:50,983
It's not like the most          
engaging lecture, so            

24
00:00:51,051 --> 00:00:52,850
I'll try to be as               
engaging as possible, but       

25
00:00:52,919 --> 00:00:54,786
uh, it is actually              
super useful.                   

26
00:00:54,855 --> 00:00:56,922
So if, if I want you to have    
like one take away from,        

27
00:00:56,991 --> 00:00:59,757
from this whole talk, it's      
that, if you wanna get good at  

28
00:00:59,826 --> 00:01:01,893
using Xcode and you wanna feel  
fluent when you're using it,    

29
00:01:01,962 --> 00:01:04,096
you actually need to know       
a lot of key commands.          

30
00:01:04,164 --> 00:01:05,330
It will really help you a lot.  

31
00:01:07,668 --> 00:01:09,968
Xcode from Paul in lectures     
but actually learning all the   

32
00:01:10,037 --> 00:01:12,437
shortcuts for everything will   
make your life way simpler.     

33
00:01:12,506 --> 00:01:14,339
And I hope I can kinda          
convince you today that all     

34
00:01:14,408 --> 00:01:16,208
this stuff is actually          
pretty intuitive.               

35
00:01:16,276 --> 00:01:18,276
It's not just like memorizing   
a bunch of random things, but   

36
00:01:18,345 --> 00:01:20,678
it's all laid out by Apple      
in a very nice and, and         

37
00:01:20,747 --> 00:01:21,346
orderly way.                    

38
00:01:23,717 --> 00:01:25,651
So let's just dive right in.    

39
00:01:25,719 --> 00:01:29,287
I'm gonna pop up an Xcode here  
and I have Concentration open,  

40
00:01:29,356 --> 00:01:31,856
which is the end of             
Wednesday's lecture,            

41
00:01:31,925 --> 00:01:33,392
we had this code working.       

42
00:01:33,460 --> 00:01:36,761
The catch here though is that   
this version of Concentration   

43
00:01:36,830 --> 00:01:40,399
that I'm using right now, I've  
deemed it sad Concentration.    

44
00:01:40,467 --> 00:01:41,433
You can see right               
here on this folder,            

45
00:01:43,470 --> 00:01:45,971
we're gonna investigate         
that using the debugger.        

46
00:01:46,039 --> 00:01:48,039
But before we do that,          
I am gonna hop in and           

47
00:01:48,108 --> 00:01:51,309
give you a tour of Xcode using  
key commands and what not.      

48
00:01:51,378 --> 00:01:54,713
So you remember things from     
lecture where you've seen for   

49
00:01:54,782 --> 00:01:56,415
example, you can navigate       
around all the panes            

50
00:01:56,484 --> 00:01:58,583
by clicking these various       
buttons, but it's gonna         

51
00:01:58,652 --> 00:02:00,318
get really old really           
fast when you're coding.        

52
00:02:00,387 --> 00:02:00,886
If you're also                  

53
00:02:02,989 --> 00:02:04,823
You can get like five           
times faster if you just        

54
00:02:06,493 --> 00:02:08,159
learn how things are laid       
out in some various things.     

55
00:02:08,228 --> 00:02:10,228
So the first thing,             
I'll just kinda go,             

56
00:02:10,297 --> 00:02:12,497
go through Xcode in order,      
kinda from the top left.        

57
00:02:12,566 --> 00:02:15,767
The first thing is, all this    
stuff up here at the top left,  

58
00:02:15,836 --> 00:02:17,836
you can actually do             
automated by key commands.      

59
00:02:17,905 --> 00:02:20,371
So instead of going up and      
clicking Run and what not,      

60
00:02:20,440 --> 00:02:22,374
you can do Cmd+R,               
and that will run.              

61
00:02:24,912 --> 00:02:26,110
So there,                       
there are key commands for      

62
00:02:26,179 --> 00:02:28,246
controlling everything about    
running and, and stopping and   

63
00:02:28,315 --> 00:02:29,515
all that stuff.                 

64
00:02:29,583 --> 00:02:32,184
Um, the next thing I wanna      
talk about is more important    

65
00:02:32,252 --> 00:02:35,487
which is just how you actually  
navigate around all of Xcode.   

66
00:02:35,555 --> 00:02:38,657
And so there are key commands   
for doing things like, if you   

67
00:02:38,725 --> 00:02:41,927
watch the screen right now,     
I can do this, this, this.      

68
00:02:43,597 --> 00:02:45,063
You get really fast             
at this stuff.                  

69
00:02:46,867 --> 00:02:49,334
We're, were opening up          
a second editor right now.      

70
00:02:50,503 --> 00:02:50,936
Right, so                       

71
00:02:53,473 --> 00:02:55,840
how you can like quickly        
get your way around Xcode.      

72
00:02:55,909 --> 00:02:59,144
So when I close everything      
that I just did.                

73
00:02:59,213 --> 00:03:01,513
Suppose that were at a full     
main screen like this,          

74
00:03:01,582 --> 00:03:03,982
the way that everything is      
laid out is very logical,       

75
00:03:04,051 --> 00:03:06,852
where the left-most pane,       
which is called the Navigator,  

76
00:03:06,920 --> 00:03:08,152
is controlled by Cmd+0.         

77
00:03:08,221 --> 00:03:10,688
That's what shows it.           

78
00:03:10,757 --> 00:03:14,692
And then the right-most pane    
is showed using Cmd+Option+0.   

79
00:03:14,761 --> 00:03:18,130
That's what shows and           
hides the op, right-most pane.  

80
00:03:18,198 --> 00:03:21,633
And then within each pane,      
so if I'm on the left pane,     

81
00:03:21,702 --> 00:03:25,837
if I do Cmd+1,2,3,4,5 you see   
how up on the top left here     

82
00:03:25,906 --> 00:03:28,072
we're going through             
these tabs?                     

83
00:03:28,141 --> 00:03:30,976
1, 2, 3, 4, 5, right?           

84
00:03:31,045 --> 00:03:33,011
And then if I do Cmd+Option+0,  
and                             

85
00:03:33,079 --> 00:03:36,414
I look at these tabs up here,   
I just do Cmd+Option+1, 2 and   

86
00:03:36,483 --> 00:03:38,950
I can go through                
all those tabs.                 

87
00:03:39,019 --> 00:03:40,686
So it's actually pretty         
nicely laid out like that.      

88
00:03:40,754 --> 00:03:43,287
You just remember that, Cmd+0   
is for showing and hiding and   

89
00:03:43,356 --> 00:03:44,623
then the numbers are for        
tabbing.                        

90
00:03:44,691 --> 00:03:47,058
And then if you add in Option,  
it does the right side.         

91
00:03:47,127 --> 00:03:48,560
So it's pretty simple.          

92
00:03:48,628 --> 00:03:52,464
If you just do Cmd+Shift+y,     
it toggles the console and      

93
00:03:52,532 --> 00:03:56,168
the debugger at the bottom      
which we'll be working with     

94
00:03:56,236 --> 00:03:57,469
more later today.               

95
00:03:57,538 --> 00:03:59,504
And those commands alone are    
enough to just kind of like     

96
00:03:59,573 --> 00:04:00,939
constantly manage               
your window size,               

97
00:04:01,008 --> 00:04:02,874
especially if you're            
programming on a laptop where   

98
00:04:02,943 --> 00:04:04,676
you only have like limited      
screen real estate.             

99
00:04:04,745 --> 00:04:07,812
It's actually really nice to    
be able to use those commands   

100
00:04:07,881 --> 00:04:09,881
to quickly navigate around.     

101
00:04:09,949 --> 00:04:12,717
The next thing I'll point out   
is that, you know from lecture  

102
00:04:12,786 --> 00:04:15,687
that Xcode has uh,              
two different editors.          

103
00:04:15,755 --> 00:04:18,757
It has the um, the main editor  
that we' re in right here, and  

104
00:04:18,826 --> 00:04:21,726
it has also this thing          
called the assistant editor.    

105
00:04:21,795 --> 00:04:27,132
So if we do                     
a Cmd+Option+Enter.             

106
00:04:27,201 --> 00:04:29,834
It pops up in this second       
pane over here, and             

107
00:04:29,903 --> 00:04:33,171
then we can do Cmd+Enter to     
go back to just one pane, so    

108
00:04:33,240 --> 00:04:35,207
this is super useful.           

109
00:04:35,275 --> 00:04:37,842
The one thing that I'll point   
out about this is that,         

110
00:04:37,911 --> 00:04:41,380
if you go to your,              
your Xcode preferences window,  

111
00:04:41,448 --> 00:04:43,949
we have all these things that   
we can, that we can toggle and  

112
00:04:44,017 --> 00:04:44,549
we won't go through all         

113
00:04:46,519 --> 00:04:47,919
You can go around and           
change your font colors and     

114
00:04:47,988 --> 00:04:49,054
all that good stuff.            

115
00:04:51,658 --> 00:04:54,559
recommend that you utilize,     
which is in Navigation here.    

116
00:04:54,628 --> 00:04:57,896
There's this little check box   
that says, Navigation uses      

117
00:04:57,965 --> 00:05:01,199
the primary editor, versus      
using the focused editor, and   

118
00:05:01,268 --> 00:05:04,235
by default, this is set to      
using the primary editor.       

119
00:05:04,304 --> 00:05:07,539
And that's going to probably    
torture you if you use certain  

120
00:05:07,608 --> 00:05:09,006
other key commands.             

121
00:05:09,075 --> 00:05:10,542
Let me give you an example.     

122
00:05:10,610 --> 00:05:13,511
One of the key commands is for  
opening certain files without   

123
00:05:13,580 --> 00:05:15,146
having to navigate              
there in the,                   

124
00:05:15,215 --> 00:05:16,815
in the file                     
navigator over here.            

125
00:05:16,883 --> 00:05:19,450
So let's say that I,            
we all know that there's        

126
00:05:19,519 --> 00:05:22,454
a file called Card.swift and    
we wanna open it, all I         

127
00:05:22,523 --> 00:05:25,490
have to do is Cmd+Shift+O for   
open, type card, and            

128
00:05:25,559 --> 00:05:29,327
then there's Card.swift,        
and that will open it up.       

129
00:05:29,396 --> 00:05:30,128
Now what if I wanted            

130
00:05:32,900 --> 00:05:35,199
So right here,                  
I am zooming around in the,     

131
00:05:35,268 --> 00:05:37,268
in the right pane and I have    
the right pane selected.        

132
00:05:37,337 --> 00:05:39,670
If I do Cmd+Shift+O and         
I go back to ViewController,    

133
00:05:39,739 --> 00:05:42,707
it still opens in               
the left pane.                  

134
00:05:42,775 --> 00:05:45,309
So if you don't have this use   
focused editor option selected  

135
00:05:45,378 --> 00:05:47,378
it's always going to            
use the left editor or          

136
00:05:47,447 --> 00:05:49,180
the prime editor for            
those key commands.             

137
00:05:49,249 --> 00:05:52,150
So that's why you wanna have    
this box checked, so that now   

138
00:05:52,218 --> 00:05:55,086
when we go over here and        
we have the right one selected  

139
00:05:55,155 --> 00:05:57,655
and we do card, it opens        
it over on the right pan.       

140
00:05:57,724 --> 00:05:58,990
Makes sense?                    

141
00:05:59,059 --> 00:06:02,526
Cool, so I highly               
recommend that you do that.     

142
00:06:02,595 --> 00:06:05,596
Okay, the next thing,           
we're gonna do is actually      

143
00:06:05,665 --> 00:06:08,566
talk about text editing within  
each window really briefly.     

144
00:06:08,635 --> 00:06:11,369
One thing that I wanna point    
out is, you haven't dealt with  

145
00:06:11,437 --> 00:06:14,038
this problem yet because your   
Xcode projects haven't gotten   

146
00:06:14,107 --> 00:06:15,907
very large, but                 
they will get very large.       

147
00:06:15,976 --> 00:06:17,241
There will be lots              
of code files and               

148
00:06:17,310 --> 00:06:19,344
eventually you'll have          
hundreds of files in a single   

149
00:06:19,413 --> 00:06:21,579
project when you're making      
a big Xcode project.            

150
00:06:21,648 --> 00:06:24,682
And one of the things that      
will help you navigate that is  

151
00:06:24,751 --> 00:06:27,452
to help yourself by             
leaving Navigation,             

152
00:06:27,521 --> 00:06:30,688
like Navigation helper things   
throughout your files and       

153
00:06:30,757 --> 00:06:33,524
one way to do that is this      
comment right here that is      

154
00:06:33,593 --> 00:06:35,259
prefixed with comment mark.     

155
00:06:35,295 --> 00:06:35,326
excuse me.                      

156
00:06:37,731 --> 00:06:38,363
below this line.                

157
00:06:41,134 --> 00:06:43,535
this notification in            
this window up here.            

158
00:06:43,604 --> 00:06:44,936
That's where card               
touch behavior is and           

159
00:06:45,004 --> 00:06:46,270
it will jump to that            
point of the file.              

160
00:06:46,339 --> 00:06:48,306
And so you can imagine in big   
files, using these marks is     

161
00:06:48,375 --> 00:06:50,241
actually super helpful          
when they're really long,       

162
00:06:50,309 --> 00:06:51,543
something to navigate around.   

163
00:06:53,313 --> 00:06:56,013
The next thing that I'll point  
out about text editing is,      

164
00:06:56,082 --> 00:06:58,850
it's very useful just to know   
basic text editing commands.    

165
00:06:58,919 --> 00:07:01,386
Like for example, if you        
have many lines selected and    

166
00:07:01,454 --> 00:07:03,821
you want to comment them        
out all of a sudden,            

167
00:07:03,890 --> 00:07:07,758
just Cmd+/ will comment         
things out like that and        

168
00:07:07,827 --> 00:07:10,295
then Cmd+/ again                
will undo them.                 

169
00:07:10,363 --> 00:07:12,897
Another maybe even more useful  
thing is when you get yourself  

170
00:07:12,966 --> 00:07:15,100
into a,                         
a nasty state like this.        

171
00:07:17,070 --> 00:07:19,437
Just mess some stuff up for     
no reason.                      

172
00:07:19,506 --> 00:07:21,372
And you can tell that it's      
really not formatted.           

173
00:07:21,441 --> 00:07:23,074
We can select everything        
that we want and                

174
00:07:23,143 --> 00:07:25,743
do Ctrl+I, I for                
indent and it will just         

175
00:07:25,812 --> 00:07:28,179
magically put everything        
exactly like we wanted.         

176
00:07:28,248 --> 00:07:29,747
So that'll save you a lot       
of time and headache,           

177
00:07:29,816 --> 00:07:31,516
if things are not, if you,      

178
00:07:31,585 --> 00:07:33,951
if you can't tell things that   
are nicely indented or not.     

179
00:07:34,020 --> 00:07:36,054
And I'll list these all         
online on Piazza by the way,    

180
00:07:36,122 --> 00:07:37,922
so it's not like you need       
to know down what they are.     

181
00:07:37,991 --> 00:07:39,324
I just kinda want               
to give you the,                

182
00:07:39,393 --> 00:07:41,426
give you the lay                
of the land here.               

183
00:07:41,495 --> 00:07:43,795
So hopefully we're through      
the, the fast sorta boring      

184
00:07:43,863 --> 00:07:46,364
part of the lecture where it's  
just all of the key commands.   

185
00:07:46,433 --> 00:07:48,199
But I highly recommend that     
you learn all this stuff and    

186
00:07:48,267 --> 00:07:49,967
start getting it into           
your muscle memory so           

187
00:07:50,036 --> 00:07:51,436
that when you're                
navigating on Xcode,            

188
00:07:51,505 --> 00:07:54,206
you're not torturing yourself   
for having to click around      

189
00:07:54,274 --> 00:07:56,941
everywhere and                  
do everything manually.         

190
00:07:57,010 --> 00:07:59,277
The next thing to do is         
to actually start using         

191
00:07:59,346 --> 00:08:00,111
the debugger.                   

192
00:08:02,416 --> 00:08:04,449
we're not actually using        
the version of concentration    

193
00:08:04,518 --> 00:08:06,284
directly from the end           
of Wednesday's lecture.         

194
00:08:06,353 --> 00:08:08,587
We're actually using a          
slightly broken version of it,  

195
00:08:08,655 --> 00:08:11,088
and so let's see what happens   
when we actually run this one.  

196
00:08:11,157 --> 00:08:13,991
I'm gonna run it on             
the iPhone X simulator using    

197
00:08:14,060 --> 00:08:17,929
our trusty Cmd+R key command,   
and let's see what happens.     

198
00:08:30,043 --> 00:08:32,843
So I've crashed, it doesn't     
even work right from            

199
00:08:32,912 --> 00:08:35,747
the start, and we're thrown     
to the app delegate,            

200
00:08:35,815 --> 00:08:37,515
which is the main file.         

201
00:08:37,584 --> 00:08:39,551
It's crashing on the main       
method it says, but             

202
00:08:39,619 --> 00:08:40,785
that's not very helpful.        

203
00:08:40,854 --> 00:08:43,021
So the way that we first        
get more insight into this,     

204
00:08:43,090 --> 00:08:44,756
is to look into                 
the actual stack trace,         

205
00:08:44,824 --> 00:08:46,691
which shows up in               
the console log down here.      

206
00:08:46,760 --> 00:08:48,325
And you just see this           
huge stack trace,               

207
00:08:48,394 --> 00:08:50,361
which goes all the way          
into the internals of iOS,      

208
00:08:50,430 --> 00:08:51,730
all the way down                
through UI kit,                 

209
00:08:51,798 --> 00:08:53,665
and core foundation,            
and all this stuff, and         

210
00:08:53,734 --> 00:08:56,100
it's not very helpful to see    
all these memory addresses.     

211
00:08:56,169 --> 00:08:59,737
But if you scroll up to the     
top in almost every case you    

212
00:08:59,806 --> 00:09:02,140
will see what                   
the actual reason for           

213
00:09:02,208 --> 00:09:04,009
terminating the app was.        

214
00:09:04,077 --> 00:09:07,345
And in this case it tells       
us that there's an uncaught     

215
00:09:07,414 --> 00:09:10,081
exception called                
UnknownKeyException,            

216
00:09:10,150 --> 00:09:12,683
which we may might not          
know what that is.              

217
00:09:12,752 --> 00:09:16,253
It tells us that the reason     
for the crash was, oops,        

218
00:09:16,322 --> 00:09:16,821
sorry.                          

219
00:09:16,890 --> 00:09:17,622
The reason for                  

220
00:09:20,727 --> 00:09:23,727
so it already tells us what     
file something is happening     

221
00:09:23,796 --> 00:09:26,731
in, has some error on           
setValue:forUndefinedKey.       

222
00:09:26,799 --> 00:09:28,433
Unclear exactly what that is,   

223
00:09:28,501 --> 00:09:31,502
cuz we didn't write that        
method, and then this class is  

224
00:09:31,571 --> 00:09:35,006
not key value coding-compliant  
for the key flipCountLabel.     

225
00:09:35,075 --> 00:09:39,710
So that gives us even more      
insight, is something is wrong  

226
00:09:39,779 --> 00:09:44,715
with flipCountLabel, and so     
if we go into view controller,  

227
00:09:44,784 --> 00:09:47,752
and we go check out             
flipCountLabel,                 

228
00:09:47,820 --> 00:09:52,590
we actually see flipCountLabel  
abbreviated to LBL here,        

229
00:09:52,659 --> 00:09:56,027
which is not what it            
says in the debugger.           

230
00:09:56,096 --> 00:09:58,896
Can anyone figure out what's    
actually going on here?         

231
00:09:58,965 --> 00:10:00,599
How does it know to print       
out flipCountLabel?             

232
00:10:01,934 --> 00:10:02,900
Any ideas?                      

233
00:10:02,969 --> 00:10:05,804
If we've named                  
it flipCountLbl,                

234
00:10:05,872 --> 00:10:09,641
then why is it printing         
out flipCountLabel?             

235
00:10:09,709 --> 00:10:11,008
Can anyone think of why?        

236
00:10:11,077 --> 00:10:13,011
No?                             

237
00:10:13,079 --> 00:10:14,179
Yeah, in the back.              

238
00:10:17,817 --> 00:10:18,583
Yeah, exactly.                  

239
00:10:18,652 --> 00:10:19,751
So that's what I named it.      

240
00:10:19,819 --> 00:10:20,418
What he said was,               

241
00:10:22,622 --> 00:10:24,655
So if we go over to             
the storyboard over here,       

242
00:10:24,724 --> 00:10:27,591
actually let's just open up     
both side-by-side using all of  

243
00:10:27,660 --> 00:10:29,094
our happy new key commands.     

244
00:10:31,631 --> 00:10:33,064
So we got the storyboard        
open over here.                 

245
00:10:38,438 --> 00:10:39,804
I'm gonna make this             
fullscreen for a moment,        

246
00:10:39,872 --> 00:10:41,239
cuz it's easier to              
see what's going on.            

247
00:10:43,810 --> 00:10:44,476
If we look inside here,         

248
00:10:48,781 --> 00:10:51,782
Now this right here,            
that I've selected,             

249
00:10:51,851 --> 00:10:54,685
is not actually the official    
name of the object.             

250
00:10:54,754 --> 00:10:58,390
If I open up our assistant      
editor over here, and           

251
00:10:58,458 --> 00:11:00,558
I go over to the view           
controller, and                 

252
00:11:00,627 --> 00:11:03,494
I look at its rightmost pane,   
this is where we see all of     

253
00:11:03,563 --> 00:11:04,663
the things that                 
we've connected, and            

254
00:11:06,633 --> 00:11:09,567
on the storyboard what they're  
actually connected to.          

255
00:11:09,636 --> 00:11:11,569
Here's where you see            
that we have this outlet.       

256
00:11:11,638 --> 00:11:14,271
The name of the outlet is       
Flip Count Label, and it's      

257
00:11:14,340 --> 00:11:17,175
connected to flipCountLabel,    
but if you zoom in here,        

258
00:11:17,244 --> 00:11:20,244
you'll notice that there's      
a little exclamation point or   

259
00:11:20,313 --> 00:11:22,714
an empty thing,                 
as compared to the normal dot.  

260
00:11:22,783 --> 00:11:24,682
So that's it telling you that   
this thing actually can't       

261
00:11:24,751 --> 00:11:27,318
find what it's                  
actually connected to.          

262
00:11:27,387 --> 00:11:29,654
So if we go back over           
into our View Controller,       

263
00:11:29,723 --> 00:11:30,655
in this editor, and             

264
00:11:38,865 --> 00:11:41,166
And then we go back to          
the storyboard editor,          

265
00:11:41,234 --> 00:11:44,035
we should see that, that        
error is no longer there, and   

266
00:11:44,103 --> 00:11:46,504
we actually have                
Flip Count Label connected.     

267
00:11:46,573 --> 00:11:49,407
So this is a bug that you'll    
probably see often at first,    

268
00:11:49,476 --> 00:11:52,377
as you're not quite, I mean,    
it's just hard to keep your     

269
00:11:52,445 --> 00:11:54,745
storyboard in sync with         
your code sometimes.            

270
00:11:54,814 --> 00:11:57,581
So just know that there's this  
error about key value coding    

271
00:11:57,650 --> 00:11:59,484
compliance and                  
that's what it means.           

272
00:11:59,553 --> 00:12:01,152
That you should go              
check this right most           

273
00:12:01,220 --> 00:12:03,120
pane with your                  
View Controller selected, and   

274
00:12:03,189 --> 00:12:04,956
that will help you get          
rid of these errors.            

275
00:12:05,025 --> 00:12:06,524
Cool, so                        
we're gonna save that, and      

276
00:12:06,592 --> 00:12:07,759
then we're gonna run it.        

277
00:12:16,569 --> 00:12:18,803
Okay great, so                  
it's actually running now.      

278
00:12:18,872 --> 00:12:21,272
So if you click around          
to play the game.               

279
00:12:21,341 --> 00:12:26,243
Oops, it crashed, and so if I   
look down inside the console    

280
00:12:26,312 --> 00:12:29,713
here, I don't actually          
have any logs.                  

281
00:12:29,782 --> 00:12:32,316
It didn't actually show me in   
the console why it crashed.     

282
00:12:32,385 --> 00:12:34,919
In fact,                        
I have no info anywhere.        

283
00:12:34,987 --> 00:12:36,220
Let's try and run it again and  

284
00:12:36,289 --> 00:12:38,356
see if we can figure out        
what causes it to crash.        

285
00:12:38,425 --> 00:12:39,557
It looked like that             
time it crashed when            

286
00:12:39,626 --> 00:12:40,291
I clicked on a card.            

287
00:12:43,763 --> 00:12:47,365
Okay, that time, it let me      
click on one of the cards, but  

288
00:12:47,434 --> 00:12:50,735
it still crashed, so            
let's try it again.             

289
00:12:50,803 --> 00:12:52,770
Let's see if we can figure      
out some sort of pattern for    

290
00:12:52,839 --> 00:12:53,638
what's going on.                

291
00:12:56,509 --> 00:12:59,076
That time it crashed            
after four cards.               

292
00:12:59,145 --> 00:13:01,679
So does anyone have an idea     
for how we can actually start   

293
00:13:01,748 --> 00:13:03,414
figuring out how                
to debug this?                  

294
00:13:03,482 --> 00:13:04,015
Like how on Earth are we        

295
00:13:05,485 --> 00:13:08,386
It seems to be crashing         
randomly after some number      

296
00:13:08,455 --> 00:13:09,220
of cards, and                   

297
00:13:15,795 --> 00:13:16,728
Anyone have an idea?            

298
00:13:18,531 --> 00:13:20,898
Even if you think it's silly,   
just say something.             

299
00:13:20,967 --> 00:13:22,200
Say one way we can do this.     

300
00:13:22,268 --> 00:13:23,034
Print statements?               

301
00:13:23,102 --> 00:13:23,935
Yeah, print statements.         

302
00:13:25,671 --> 00:13:27,538
frustrating if you were in      
a really big app though.        

303
00:13:27,607 --> 00:13:29,106
But you already see             
the problem with print          

304
00:13:29,175 --> 00:13:31,175
statements is, if we're         
gonna use print statements,     

305
00:13:31,244 --> 00:13:33,311
what the heck are we gonna do,  
go inside every method, and     

306
00:13:33,380 --> 00:13:34,812
type print at every             
point in the method,            

307
00:13:34,881 --> 00:13:36,514
and figure out where,           
and what's going on?            

308
00:13:36,583 --> 00:13:37,849
We have to inspect              
our entire app,                 

309
00:13:37,917 --> 00:13:40,484
imagine we had like a 100,000   
lines of code that'd be really  

310
00:13:40,553 --> 00:13:41,085
frustrating.                    

311
00:13:44,424 --> 00:13:47,558
think about when the actual     
app is crashing.                

312
00:13:47,626 --> 00:13:49,593
At what point is it crashing?   

313
00:13:49,662 --> 00:13:51,662
When you flip a card.           

314
00:13:51,731 --> 00:13:52,830
When I flip a card.             

315
00:13:52,899 --> 00:13:54,065
Can you use a break             
point somewhere?                

316
00:13:54,133 --> 00:13:56,034
Bingo, so you say,              
just using a break point,       

317
00:13:56,102 --> 00:13:58,369
because it's definitely         
crashing when we flip a card.   

318
00:13:58,438 --> 00:13:59,571
So that's a new idea.           

319
00:14:03,409 --> 00:14:04,908
inside that method.             

320
00:14:04,977 --> 00:14:07,378
And then that will help         
us hopefully figure out,        

321
00:14:07,447 --> 00:14:10,281
when the crashing happens       
we'll be able to step through,  

322
00:14:10,350 --> 00:14:12,517
and hopefully figure            
out what's going on.            

323
00:14:12,585 --> 00:14:14,319
So the way break                
points work in Xcode,           

324
00:14:14,387 --> 00:14:16,888
and if you haven't used break   
points before it's a way        

325
00:14:16,956 --> 00:14:19,457
for your debugger to pause      
execution of your program on    

326
00:14:19,525 --> 00:14:21,258
a certain line of code.         

327
00:14:21,327 --> 00:14:23,628
So if we go inside              
the touchCard method,           

328
00:14:23,696 --> 00:14:24,995
which is we know,               
the first thing that            

329
00:14:25,064 --> 00:14:27,465
happens directly when           
we click on a card.             

330
00:14:27,533 --> 00:14:30,701
We can click over here on the   
left pane on the line of code,  

331
00:14:30,770 --> 00:14:32,437
and it pops up this             
little blue arrow, and          

332
00:14:32,505 --> 00:14:33,871
that's what a break point is.   

333
00:14:33,940 --> 00:14:36,307
And that instructs the          
debugger to please stop there   

334
00:14:36,375 --> 00:14:37,175
when we get there.              

335
00:14:40,380 --> 00:14:43,447
in the left down here, and      
you can see that it has this    

336
00:14:43,516 --> 00:14:46,551
little blue arrow that looks    
just like this one, and         

337
00:14:46,619 --> 00:14:48,753
when I click on it              
it turns into grey,             

338
00:14:48,821 --> 00:14:51,189
which means break               
points are disabled.            

339
00:14:51,257 --> 00:14:53,223
All break points in the entire  
program are disabled, so        

340
00:14:53,292 --> 00:14:55,293
if you want break points to be  
enabled you have to activate    

341
00:14:55,362 --> 00:14:56,628
them this way.                  

342
00:14:56,696 --> 00:14:59,563
There's also a pane, up inside  
the navigator over here,        

343
00:14:59,632 --> 00:15:02,400
that looks the same way, and    
it'll show you a list of all    

344
00:15:02,468 --> 00:15:04,835
your break points throughout    
your entire Xcode project.      

345
00:15:04,904 --> 00:15:06,037
So, you can also go             
up here to this pane.           

346
00:15:08,441 --> 00:15:09,874
do with break points            
than just this.                 

347
00:15:09,943 --> 00:15:12,877
You can also go to this little  
plus at the bottom left of      

348
00:15:12,946 --> 00:15:16,180
this pane, and you can set      
certain special break points.   

349
00:15:16,248 --> 00:15:18,916
So for example, there's one     
called an exception break       

350
00:15:18,985 --> 00:15:21,051
point, so if I add that,        
what this does is,              

351
00:15:21,120 --> 00:15:22,687
anytime an exception            
is thrown,                      

352
00:15:22,755 --> 00:15:24,555
if you throw an exception       
in your app,                    

353
00:15:24,624 --> 00:15:27,391
instead of just throwing the    
exception to the console, or    

354
00:15:27,460 --> 00:15:30,528
crashing, or what not, it'll    
actually always, by default,    

355
00:15:30,597 --> 00:15:32,963
open the debugger and           
pause on that line of code.     

356
00:15:33,032 --> 00:15:34,732
So if you just always           
have this all exceptions        

357
00:15:34,800 --> 00:15:36,467
break point running             
that will actually help         

358
00:15:36,535 --> 00:15:38,002
you in your developing for      
example, so                     

359
00:15:38,070 --> 00:15:40,204
you can actually customize      
break points here that way.     

360
00:15:40,273 --> 00:15:42,840
You can also disable            
individual break points from    

361
00:15:42,909 --> 00:15:43,474
this pane.                      

362
00:15:46,112 --> 00:15:47,879
the one that we just            
set right here, but             

363
00:15:47,947 --> 00:15:50,514
this one that I just mentioned  
about exceptions causing        

364
00:15:50,583 --> 00:15:52,783
break points to happen,         
this one is disabled.           

365
00:15:52,852 --> 00:15:54,452
So you can selectively          
go enable and                   

366
00:15:54,520 --> 00:15:56,988
disable break points all        
across every file off on this   

367
00:15:57,056 --> 00:15:58,756
one pane, which is nice.        

368
00:15:58,824 --> 00:16:00,224
But oftentimes all              
that you need to do,            

369
00:16:00,292 --> 00:16:02,059
I'm gonna disable               
the exceptions one.             

370
00:16:02,128 --> 00:16:04,161
Oftentimes all that you need    
to do is actually within        

371
00:16:04,230 --> 00:16:07,331
an individual file, set the     
break point in that one file.   

372
00:16:07,400 --> 00:16:09,033
So okay if we run               
the program now.                

373
00:16:13,572 --> 00:16:16,507
When I click on a card we'll    
see that what happens is we     

374
00:16:16,576 --> 00:16:18,176
end up on this line of code.    

375
00:16:19,312 --> 00:16:21,712
So the program is paused at     

376
00:16:21,781 --> 00:16:24,048
this line where we're           
setting off the card number.    

377
00:16:24,116 --> 00:16:26,250
And the first thing to point    
out is that you'll notice       

378
00:16:26,319 --> 00:16:28,619
in the debugger itself we       
actually have a trace of        

379
00:16:28,688 --> 00:16:31,355
everything that's stored off    
in memory at this point.        

380
00:16:31,424 --> 00:16:34,625
So self would refer to the      
view controller in this case.   

381
00:16:34,694 --> 00:16:36,160
And you can see if I zoom in,   
you can see                     

382
00:16:36,229 --> 00:16:38,096
that it says concentration      
view controller and             

383
00:16:38,164 --> 00:16:40,464
this is the memory address      
of the view controller, but     

384
00:16:40,533 --> 00:16:42,867
it not only gives you that,     
it gives you a drop down menu   

385
00:16:42,936 --> 00:16:45,669
with all of the things that     
are instance variables          

386
00:16:45,738 --> 00:16:49,040
stored off on that              
instance of that class.         

387
00:16:49,108 --> 00:16:53,911
So things like we have the      
instance of the actual game     

388
00:16:53,980 --> 00:16:57,048
of concentration and that has   
lots of properties itself.      

389
00:16:57,116 --> 00:17:00,184
If it has the array of cards    
and then it also has that       

390
00:17:00,252 --> 00:17:02,786
variable index of the one and   
only face up card, and we can   

391
00:17:02,855 --> 00:17:05,957
expand cards and we can look    
into each card and then we can  

392
00:17:06,026 --> 00:17:07,959
find out that the identifier    
for that card is five.          

393
00:17:08,027 --> 00:17:10,461
So you can actually see all of  
the things that are stored off  

394
00:17:10,529 --> 00:17:13,163
right here,                     
inside of the debugger, so      

395
00:17:13,232 --> 00:17:17,034
that's super nice, and we can   
do that, use that to confirm    

396
00:17:17,103 --> 00:17:20,438
something like maybe we         
want to make sure that.         

397
00:17:20,506 --> 00:17:21,839
The identifiers that we've set  

398
00:17:21,908 --> 00:17:24,408
actually have an equal          
number of pairs of options.     

399
00:17:24,477 --> 00:17:26,544
So, if we go through,we         
see that the first one is       

400
00:17:26,612 --> 00:17:29,013
identifier five, the second     
one has identifier three,       

401
00:17:29,082 --> 00:17:29,913
third one has four.             

402
00:17:29,982 --> 00:17:32,583
Four, okay great,               
here's a pair.                  

403
00:17:32,652 --> 00:17:34,818
We shouldn't see another four,  
right?                          

404
00:17:34,887 --> 00:17:37,688
There's a one and               
we should see,                  

405
00:17:37,756 --> 00:17:41,325
we should see one through six,  
correct?                        

406
00:17:41,394 --> 00:17:42,660
And we should see               
each one twice, so              

407
00:17:42,729 --> 00:17:44,795
anyway, that'll be like a way   
to figure that out quickly      

408
00:17:44,864 --> 00:17:46,864
without having go manually and  
print everything out.           

409
00:17:46,932 --> 00:17:49,967
Another thing that we can do    
at any given point is over      

410
00:17:50,036 --> 00:17:53,336
inside the console, LLDB,       
stands for your debugger,       

411
00:17:53,405 --> 00:17:55,740
the DB part stands for          
debugger.                       

412
00:17:55,808 --> 00:17:58,309
We can actually print out any   
object that we want to be able  

413
00:17:58,378 --> 00:17:59,076
to inspect it.                  

414
00:17:59,145 --> 00:18:00,111
So if I do a PO,                

415
00:18:05,518 --> 00:18:06,784
Give it a moment.               

416
00:18:06,853 --> 00:18:10,254
And you notice it prints out    
this optional concentration,    

417
00:18:10,323 --> 00:18:12,990
because concentration           
is of type optional.            

418
00:18:13,059 --> 00:18:14,458
In this case, it's what's       
called an implicitly            

419
00:18:14,527 --> 00:18:15,326
unwrapped optional.             

420
00:18:18,531 --> 00:18:19,897
In other words, it's not nil.   

421
00:18:19,966 --> 00:18:22,132
The other value in the enum     
for an optional is sum.         

422
00:18:22,201 --> 00:18:24,902
So we know that                 
concentration is set here.      

423
00:18:24,970 --> 00:18:27,871
Another thing we can do is      
actually we can print out by    

424
00:18:27,940 --> 00:18:30,741
just typing p for print so      
it just works magic             

425
00:18:32,578 --> 00:18:35,379
abilities to figure how to      
format the thing that we need   

426
00:18:35,448 --> 00:18:39,584
to print out in the way they    
think is the best readable.     

427
00:18:39,652 --> 00:18:40,485
So if I print out game,         

428
00:18:43,389 --> 00:18:47,158
prints out cards, all twelve    
values and then all the info    

429
00:18:47,227 --> 00:18:49,126
that we were just looking       
at inside the debugger.         

430
00:18:49,195 --> 00:18:51,495
But it does it all there        
formatted very nicely.          

431
00:18:51,563 --> 00:18:52,729
And then we know that           
index of one and                

432
00:18:52,798 --> 00:18:53,898
only face up card is nil so     

433
00:18:57,303 --> 00:18:58,703
We can also do that for         
any other object.               

434
00:18:58,771 --> 00:19:00,671
So I print out flipCountLabel,  

435
00:19:02,475 --> 00:19:04,542
it prints out that its          
a UI label optional.            

436
00:19:05,878 --> 00:19:09,446
It's a UI view,                 
which has a UI responder.       

437
00:19:09,515 --> 00:19:12,483
And anyway the point is p is    
very nice it's very helpful     

438
00:19:12,551 --> 00:19:13,951
for printing anything           
out whatsoever.                 

439
00:19:15,187 --> 00:19:17,387
So, I'm back to our actual      
bug, at this point.             

440
00:19:17,456 --> 00:19:20,357
We have this problem we're      
clicking on, we click           

441
00:19:20,426 --> 00:19:22,526
on a card and we're stopped     
at this break point and         

442
00:19:22,595 --> 00:19:24,962
we wanna figure out why         
this thing is crashing.         

443
00:19:25,031 --> 00:19:26,530
So the first thing              
that we might do                

444
00:19:26,599 --> 00:19:29,500
to figure out what line we're   
crashing on in this case,       

445
00:19:29,569 --> 00:19:31,135
since we're not getting         
an exception and                

446
00:19:31,204 --> 00:19:34,271
we have no idea what's going    
on, is we might go use these    

447
00:19:34,340 --> 00:19:36,974
navigation options inside       
the actual debugger here.       

448
00:19:37,042 --> 00:19:38,542
So if you look in right here,   

449
00:19:38,610 --> 00:19:40,811
we have a few different         
options right here.             

450
00:19:40,880 --> 00:19:43,047
One of them is continue         
program execution and           

451
00:19:43,115 --> 00:19:46,083
what that means is okay we're   
paused at a break point.        

452
00:19:46,152 --> 00:19:48,452
Just continue running the       
program until we hit the next   

453
00:19:48,520 --> 00:19:50,054
break point, or                 
if there are no breakpoints,    

454
00:19:50,123 --> 00:19:51,255
just continue                   
running the program.            

455
00:19:52,391 --> 00:19:53,524
So let's try that right now,    

456
00:19:53,592 --> 00:19:58,128
let's click, let's click        
on continue running.            

457
00:19:58,197 --> 00:19:59,363
Okay, in this case              
we didn't crash,                

458
00:19:59,432 --> 00:20:00,864
that time that we               
tapped on touch card,           

459
00:20:00,933 --> 00:20:02,533
so it's just continuing         
the program.                    

460
00:20:02,602 --> 00:20:04,502
We're not on a break point      
right now, so we click again.   

461
00:20:05,871 --> 00:20:07,304
Okay, we're back at             
the same break point, and       

462
00:20:07,373 --> 00:20:08,206
we can continue again.          

463
00:20:09,575 --> 00:20:12,676
Oh, and that time               
the program crashed, and        

464
00:20:12,745 --> 00:20:14,078
we're not sure                  
what's going on.                

465
00:20:14,147 --> 00:20:16,313
But we know that it definitely  
happened right after            

466
00:20:16,381 --> 00:20:17,948
this first line of touchCard.   

467
00:20:18,017 --> 00:20:22,019
So let's see how we can go      
into a little bit more detail.  

468
00:20:28,160 --> 00:20:29,693
>> Okay, so                     
we click on the card again.     

469
00:20:29,762 --> 00:20:31,996
Rather than continuing          
the execution, instead,         

470
00:20:32,064 --> 00:20:34,165
we can pick the second option   
here which is step over.        

471
00:20:36,269 --> 00:20:38,001
Oops, saw the little            
help dialog pop up for          

472
00:20:38,070 --> 00:20:39,070
a second there.                 

473
00:20:39,138 --> 00:20:40,404
I wanna get that pop            
up on the screen.               

474
00:20:43,276 --> 00:20:45,109
So you can step over            
an instruction.                 

475
00:20:47,713 --> 00:20:49,713
Let's maybe do the next         
line of code and                

476
00:20:49,782 --> 00:20:52,549
we can keep going like this     
hoping that this is the time    

477
00:20:52,618 --> 00:20:54,619
where the crush                 
actually happens.               

478
00:21:00,960 --> 00:21:03,760
And it's not, unfortunately.    

479
00:21:03,829 --> 00:21:06,162
So actually it doesn't          
help us with our problem.       

480
00:21:06,231 --> 00:21:07,331
Does anyone have                
any other ideas?                

481
00:21:11,103 --> 00:21:12,502
How do you think we can         
go further to figure            

482
00:21:12,571 --> 00:21:13,904
out what the problem            
actually is?                    

483
00:21:15,441 --> 00:21:17,608
Take a look at, take a look     
at this method here.            

484
00:21:26,718 --> 00:21:28,886
Well actually,                  
it didn't crash that time,      

485
00:21:28,955 --> 00:21:30,420
so that was kind                
of a bad exercise.              

486
00:21:30,489 --> 00:21:32,389
But I'm just saying,            
in general,                     

487
00:21:32,458 --> 00:21:35,025
once we hit the time that it    
does crash, what's something    

488
00:21:35,094 --> 00:21:37,327
else that we could do           
to actually go further?         

489
00:21:37,396 --> 00:21:40,364
Any ideas?                      
>> Set a break point.           

490
00:21:42,568 --> 00:21:43,033
>> There we go.                 

491
00:21:43,102 --> 00:21:43,668
So she just,                    

492
00:21:45,671 --> 00:21:46,671
inside concentration.           

493
00:21:48,541 --> 00:21:50,974
we're also calling other        
methods inside of touchCard.    

494
00:21:51,043 --> 00:21:52,575
And then there's another        
method after that.              

495
00:21:52,644 --> 00:21:54,611
There's also                    
updateViewFromModel,            

496
00:21:54,680 --> 00:21:55,313
so actually,                    

497
00:21:58,116 --> 00:21:59,483
Which means, it can be          
crashing anywhere inside        

498
00:21:59,552 --> 00:22:01,985
the chooseCard, or any where    
inside updateViewFromModel.     

499
00:22:02,054 --> 00:22:04,054
So one thing that we could      
do is we could go to            

500
00:22:04,123 --> 00:22:06,256
both of these methods           
like updateViewFromModel,       

501
00:22:06,325 --> 00:22:07,658
and we can set                  
a break point there.            

502
00:22:07,726 --> 00:22:12,429
And then we could pop open a,   
let's pop open card over here,  

503
00:22:12,498 --> 00:22:15,199
and we'll go to chooseCard,     
oh excuse me                    

504
00:22:15,268 --> 00:22:17,835
we're go to concentration over  
here and we'll put a break      

505
00:22:17,904 --> 00:22:20,604
point inside choose card and    
now we have three different     

506
00:22:20,673 --> 00:22:24,274
break points set as you can     
see in the break point pane.    

507
00:22:24,343 --> 00:22:28,479
And that'll make it stop at     
all the places where it could   

508
00:22:28,547 --> 00:22:30,247
possibly be at the start        
of the method.                  

509
00:22:30,315 --> 00:22:32,883
But another, I'm not gonna do   
that right now, another way of  

510
00:22:32,952 --> 00:22:37,888
doing that actually is to use   
the The next option inside      

511
00:22:37,956 --> 00:22:38,989
the debugger pane.              

512
00:22:41,961 --> 00:22:43,260
So if you click on something    

513
00:22:45,064 --> 00:22:46,664
Let me get back to              
one window here.                

514
00:22:48,567 --> 00:22:53,137
Once we get to a method,        
Like chooseCard,                

515
00:22:53,206 --> 00:22:55,572
we can see this next option     
here is step into and           

516
00:22:55,641 --> 00:22:58,074
that's how we get inside        
the actual method, so           

517
00:22:58,143 --> 00:23:01,779
if I click step into, now we    
are at the top of chooseCard.   

518
00:23:01,848 --> 00:23:04,047
And now if we want we can       
step over each line inside of   

519
00:23:04,116 --> 00:23:05,249
chooseCard.                     

520
00:23:05,317 --> 00:23:06,683
And we can inspect              
the code if we want,            

521
00:23:06,752 --> 00:23:08,452
we can read it to make          
sure everything's okay.         

522
00:23:10,757 --> 00:23:12,523
We could put extra break        
points inside here if we see    

523
00:23:12,592 --> 00:23:14,125
something that might            
be suspicious.                  

524
00:23:15,360 --> 00:23:16,559
Notice that if we're            
inside a four loop,             

525
00:23:16,628 --> 00:23:18,329
that's a lot of iterations,     

526
00:23:18,398 --> 00:23:20,764
it would take forever to        
step over the whole time.       

527
00:23:20,832 --> 00:23:22,399
So you can get yourself         
in trouble real fast            

528
00:23:22,468 --> 00:23:23,833
if you're stepping              
into methods that               

529
00:23:23,902 --> 00:23:25,202
have a lot of                   
behavior going on.              

530
00:23:25,270 --> 00:23:27,170
But that aren't relevant to     
actually what's going on.       

531
00:23:27,239 --> 00:23:28,239
But you get the idea.           

532
00:23:29,542 --> 00:23:30,107
So let's continue,              

533
00:23:33,779 --> 00:23:37,782
Let's, this time let's step     
inside updateViewFromModel.     

534
00:23:40,019 --> 00:23:41,852
So that's the method that's     
right beneath this one.         

535
00:23:42,888 --> 00:23:44,287
And let's step over this.       

536
00:23:44,356 --> 00:23:47,324
We're gonna go through all the  
indices inside cardButtons,     

537
00:23:47,393 --> 00:23:49,393
which is kind of a pain         
because we have to go           

538
00:23:49,461 --> 00:23:50,795
through this big for loop and   

539
00:23:50,863 --> 00:23:53,697
see if anyone sees anything     
suspicious in this method.      

540
00:23:56,968 --> 00:23:58,803
Just point it out,              
point it out if you see it.     

541
00:24:00,138 --> 00:24:01,405
If something weird              
is going on.                    

542
00:24:05,444 --> 00:24:07,377
Anybody?                        

543
00:24:07,446 --> 00:24:11,715
It's the world's worst          
line of code of all time.       

544
00:24:11,784 --> 00:24:12,616
What is this?                   

545
00:24:14,286 --> 00:24:14,819
What is this?                   

546
00:24:14,887 --> 00:24:15,553
Who put this here?              

547
00:24:17,656 --> 00:24:20,757
it's information this way       
to exit your app, right?        

548
00:24:20,826 --> 00:24:24,160
So we're just actually          
exiting with negative 1.        

549
00:24:24,229 --> 00:24:28,198
It turns out we're exiting a    
flipCount, which that thing we  

550
00:24:28,267 --> 00:24:31,935
keep in track of at the bottom  
of that is greater than some    

551
00:24:32,003 --> 00:24:35,538
random number that's            
generated between this.         

552
00:24:35,607 --> 00:24:36,974
What the heck?                  
This line couldn't just make    

553
00:24:37,042 --> 00:24:37,675
any sense, right?               

554
00:24:40,746 --> 00:24:44,348
debugger because it's like      
it's giving us no information   

555
00:24:44,416 --> 00:24:45,349
in the console so               

556
00:24:48,754 --> 00:24:52,022
Anyway, so obviously this is    
the problem, if we get rid      

557
00:24:52,090 --> 00:24:54,658
of this completely              
pointless in same line of       

558
00:24:54,727 --> 00:24:57,995
code that I put in there,       
then we run the program again   

559
00:25:04,437 --> 00:25:06,770
We're gonna stop at that        
break point, so maybe we'll,    

560
00:25:06,839 --> 00:25:08,038
we'll disable it this time,     

561
00:25:08,107 --> 00:25:10,207
cuz we're not sure if we        
fixed all of the problems.      

562
00:25:10,275 --> 00:25:13,010
So we'll keep that break        
point there just in case, but   

563
00:25:13,079 --> 00:25:14,644
we'll disable it and            
hit continue.                   

564
00:25:14,713 --> 00:25:16,614
And then we'll try to           
play concentration,             

565
00:25:18,351 --> 00:25:19,850
See if anything                 
strange is going on.            

566
00:25:19,919 --> 00:25:22,719
It actually seems like it's     
working more this time.         

567
00:25:22,788 --> 00:25:23,887
Also, I'm not actually          
playing right now.              

568
00:25:23,956 --> 00:25:25,389
I promise I'm not this          
bad at this game.               

569
00:25:27,026 --> 00:25:28,592
But it looks like we            
fixed the problem.              

570
00:25:28,661 --> 00:25:31,128
And we know we have fixed one   
problem because there's not     

571
00:25:31,197 --> 00:25:33,063
an exit in our code which       
is kinda ridiculous.            

572
00:25:33,132 --> 00:25:35,266
Are there any questions about   
using the actual debugger?      

573
00:25:35,334 --> 00:25:35,933
Are you done here?              

574
00:25:38,804 --> 00:25:40,069
Everyone understand kind        
of the general idea?            

575
00:25:40,138 --> 00:25:41,771
It's actually pretty simple,    
for                             

576
00:25:41,840 --> 00:25:44,007
navigating around               
the memory hierarchy and        

577
00:25:44,076 --> 00:25:46,476
then using these commands       
to step through your code.      

578
00:25:46,545 --> 00:25:47,177
That's all make sense?          

579
00:25:48,514 --> 00:25:50,747
Okay cool, one thing I          
wanna show you is that          

580
00:25:50,816 --> 00:25:52,882
the debugger is not quite as    
simple as everything that just  

581
00:25:52,951 --> 00:25:54,485
appears the pane right here.    

582
00:25:54,553 --> 00:25:56,520
It turns out that there's       
something inside of Xcode's     

583
00:25:56,589 --> 00:25:59,256
preferences called behaviors,   
and this is an Xcode            

584
00:25:59,325 --> 00:26:02,025
wide thing, it's actually       
really useful and cool.         

585
00:26:02,094 --> 00:26:04,895
And what behaviors is for       
various parts of running your   

586
00:26:04,963 --> 00:26:08,265
app, and                        
actually gives you the ability  

587
00:26:08,333 --> 00:26:11,835
to make custom configurations   
for when certain events occur.  

588
00:26:11,904 --> 00:26:13,637
You can say if this             
thing happens,                  

589
00:26:13,705 --> 00:26:15,138
then do this thing to x code.   

590
00:26:15,207 --> 00:26:18,341
So for example, right now       
when we pause inside,           

591
00:26:18,410 --> 00:26:21,311
when the app is running,        
whenever we pause,              

592
00:26:21,380 --> 00:26:25,215
we have this option here that   
says, show the navigator.       

593
00:26:26,685 --> 00:26:27,684
We have that checked.           

594
00:26:27,753 --> 00:26:30,387
So if we change this to hide,   
for example,                    

595
00:26:30,456 --> 00:26:33,524
then when the app pauses,       
watch what happens.             

596
00:26:37,896 --> 00:26:39,129
So you're gonna                 
touch on the card.              

597
00:26:40,666 --> 00:26:43,533
Did you notice that             
the navigator pane on the left  

598
00:26:43,602 --> 00:26:45,635
disappeared when                
that happened?                  

599
00:26:45,704 --> 00:26:46,370
So that's interesting.          

600
00:26:48,640 --> 00:26:51,041
we're debugging, we might want  
Xcode to just, by default,      

601
00:26:51,110 --> 00:26:53,410
just go to a certain state cuz  
we don't know whenever we're    

602
00:26:53,479 --> 00:26:55,712
running the app what state our  
Xcode is currently in, but      

603
00:26:55,781 --> 00:26:57,647
we know that when we're         
debugging we want it to be      

604
00:26:57,716 --> 00:26:58,782
in particular state.            

605
00:26:58,851 --> 00:27:00,384
So you can actually go          
customize all that stuff        

606
00:27:00,452 --> 00:27:01,652
inside behaviors.               

607
00:27:01,720 --> 00:27:03,987
In the interests of time and    
sanity, I won't go through      

608
00:27:04,056 --> 00:27:05,455
every single little option,     
like we could play              

609
00:27:05,524 --> 00:27:07,758
a sound when certain            
things happen or whatever.      

610
00:27:07,827 --> 00:27:09,560
You can actually go through     
the Behaviors pane and          

611
00:27:09,628 --> 00:27:12,862
kinda check and see everything  
that it can do for you.         

612
00:27:12,931 --> 00:27:14,932
So it's actually                
pretty useful.                  

613
00:27:15,000 --> 00:27:15,765
Any questions about behaviors?  

614
00:27:15,834 --> 00:27:16,467
Does that make sense?           

615
00:27:19,638 --> 00:27:20,571
Okay, great.                    

616
00:27:23,709 --> 00:27:26,777
a little bit about what         
actually the Xcode file itself  

617
00:27:26,845 --> 00:27:29,479
contains, because it's kind of  
opaqued people the first time   

618
00:27:29,548 --> 00:27:30,413
they have used Xcode.           

619
00:27:30,482 --> 00:27:32,448
So this is your                 
actual project file.            

620
00:27:32,517 --> 00:27:35,185
It has all these different      
tabs inside of it, and          

621
00:27:35,254 --> 00:27:38,122
there's just a lot              
going on inside here.           

622
00:27:38,190 --> 00:27:41,291
In general, I am not going to   
go through every little point,  

623
00:27:41,360 --> 00:27:43,927
but in general, what I would    
encourage you to do is          

624
00:27:43,996 --> 00:27:46,797
understand the difference       
between build settings and      

625
00:27:46,866 --> 00:27:49,866
what goes on inside of build    
settings, and build phases,     

626
00:27:49,935 --> 00:27:51,035
and what that means.            

627
00:27:53,672 --> 00:27:56,039
like figure out what version    
of our programming language     

628
00:27:56,107 --> 00:27:57,207
that we're running with.        

629
00:27:57,276 --> 00:27:58,175
That's something                
that's going to go              

630
00:27:58,244 --> 00:27:58,909
into your build settings.       

631
00:28:00,679 --> 00:28:03,780
So we can either scroll down    
and look for that option like,  

632
00:28:03,849 --> 00:28:06,883
here we find Swift language     
version set to Swift 4.0 or     

633
00:28:06,952 --> 00:28:09,586
you can actually use this       
handy thing coz this menu       

634
00:28:09,655 --> 00:28:10,987
can get kind of large, and      

635
00:28:11,056 --> 00:28:14,157
type something like language,   
and then, okay, great.          

636
00:28:14,225 --> 00:28:17,861
I was just filtering to         
just Swift language.            

637
00:28:17,929 --> 00:28:19,863
So I would encourage you to     
go through build settings,      

638
00:28:19,932 --> 00:28:22,465
and just see what things that   
there are to change and what    

639
00:28:22,534 --> 00:28:25,101
not, and you'll see this, can   
get actually kind of large,     

640
00:28:25,170 --> 00:28:27,738
the more complex your           
Xcode product is.               

641
00:28:27,807 --> 00:28:29,406
Both phases is                  
separate from that.             

642
00:28:29,475 --> 00:28:32,509
And the thing that I would      
point you towards here is,      

643
00:28:32,578 --> 00:28:33,977
this is where you see           
all the source files            

644
00:28:34,045 --> 00:28:35,179
that are used inside your app.  

645
00:28:38,917 --> 00:28:40,617
Then there's the second         
section called link             

646
00:28:40,686 --> 00:28:42,219
binary with libraries.          

647
00:28:42,287 --> 00:28:43,854
So that's if you wanna          
actually add a library          

648
00:28:43,923 --> 00:28:45,822
to use to your project which    
we are gonna get into later     

649
00:28:45,891 --> 00:28:46,457
in this quarter.                

650
00:28:49,395 --> 00:28:51,495
besides just putting            
a label or a button or          

651
00:28:51,563 --> 00:28:53,730
any of the stuff that           
comes stock in UI kit.          

652
00:28:53,799 --> 00:28:56,567
Say that we wanted to put like  
a map because we are making     

653
00:28:56,635 --> 00:28:59,469
an app like map something       
like that what we will do is    

654
00:28:59,538 --> 00:29:01,872
add a new library to our        
app and type in map, and        

655
00:29:01,940 --> 00:29:04,908
we find this thing called map   
kit, and then you type add and  

656
00:29:04,976 --> 00:29:08,044
that's where all you're adding  
for frameworks happens.         

657
00:29:08,113 --> 00:29:09,880
And then we see it created      
this new Frameworks folder      

658
00:29:09,949 --> 00:29:12,349
over here,                      
it has a MapKit inside of it.   

659
00:29:12,417 --> 00:29:15,385
And now we can go inside any    
file, like ViewController.      

660
00:29:15,454 --> 00:29:19,355
We can go to the top of that    
file and say import MapKit and  

661
00:29:19,424 --> 00:29:21,357
it's there.                     

662
00:29:21,426 --> 00:29:22,025
Make sense?                     

663
00:29:24,129 --> 00:29:25,129
the Xcode file for now.         

664
00:29:28,100 --> 00:29:30,867
The one caveat I'll talk        
about with the Xcode file is    

665
00:29:30,936 --> 00:29:33,670
if you're using Git or          
any kind of source control,     

666
00:29:33,739 --> 00:29:36,406
you will actually be            
committing the Xcode project    

667
00:29:36,474 --> 00:29:39,409
file itself to the repository   
and imagine that you're         

668
00:29:39,478 --> 00:29:42,345
working on source control       
with other people online.       

669
00:29:42,414 --> 00:29:45,048
If two different people have    
a merged conflict within        

670
00:29:45,117 --> 00:29:47,016
the actual Xcode                
project file itself,            

671
00:29:47,085 --> 00:29:49,786
that's just a big file that     
stores off a bunch of data by   

672
00:29:49,855 --> 00:29:52,656
your Xcode project, that can    
be kind of nasty to learn how   

673
00:29:52,725 --> 00:29:54,057
to merge those conflicts.       

674
00:29:54,126 --> 00:29:54,825
So that means,                  

675
00:29:56,662 --> 00:29:59,763
code it might be worth looking  
up online ways to help manage   

676
00:29:59,832 --> 00:30:02,032
the Xcode project file itself   
inside source control.          

677
00:30:02,100 --> 00:30:04,367
Cuz it's not as simple as       
doing source control inside     

678
00:30:04,436 --> 00:30:05,302
an actual code file.            

679
00:30:07,406 --> 00:30:09,939
project file that you'll wanna  
learn about what it actually    

680
00:30:10,008 --> 00:30:11,008
looks like internally.          

681
00:30:12,111 --> 00:30:13,209
So that's all that              
I have planned for              

682
00:30:13,278 --> 00:30:14,444
today does anyone               
have any questions or           

683
00:30:14,513 --> 00:30:15,345
anything that we went over.     

684
00:30:15,414 --> 00:30:16,613
Does all make sense?            

685
00:30:18,583 --> 00:30:20,083
key commands in the debugger,   
yeah sure.                      

686
00:30:20,152 --> 00:30:23,153
>> Is it possible to do some    
sort of version control?        

687
00:30:23,222 --> 00:30:23,987
>> Or right sure, so            

688
00:30:26,791 --> 00:30:29,526
So I was just sort of alluding  
to that when I was talking      

689
00:30:29,595 --> 00:30:31,861
about the Xcode                 
project file itself.            

690
00:30:31,930 --> 00:30:35,098
The answer is yes,              
you can use source control.     

691
00:30:35,166 --> 00:30:37,267
Most people, pretty much        
everybody these days uses GIT.  

692
00:30:37,335 --> 00:30:39,035
So highly recommend             
you go learn GIT.               

693
00:30:39,104 --> 00:30:42,906
If you dont know GIT,           
you can go online and quickly,  

694
00:30:42,975 --> 00:30:44,841
I would recommend, there's      
something called PRO GIT.       

695
00:30:44,910 --> 00:30:49,947
And that's a free book          
that you can learn online.      

696
00:30:50,015 --> 00:30:50,981
Learn from online.              

697
00:30:56,121 --> 00:30:58,788
Okay, great, so here's          
this book called Pro Git.       

698
00:30:58,857 --> 00:31:00,323
And if you haven't              
used Git before,                

699
00:31:00,392 --> 00:31:01,925
I highly recommend that         
you don't just go off and       

700
00:31:01,994 --> 00:31:02,859
try to use Git.                 

701
00:31:02,927 --> 00:31:04,695
I highly recommend              
that you go off and             

702
00:31:04,763 --> 00:31:06,563
you read something              
like Pro Git first.             

703
00:31:06,631 --> 00:31:09,265
So that you actually learn      
what's going on with Git and    

704
00:31:09,334 --> 00:31:11,768
how it represents source        
control under the hood.         

705
00:31:11,836 --> 00:31:14,570
It'll really help you because   
one of the big pain points for  

706
00:31:14,639 --> 00:31:17,374
people, when they are first     
learning source control is you  

707
00:31:17,442 --> 00:31:19,843
learn a few commands for        
how to commit code online and   

708
00:31:19,912 --> 00:31:21,311
how to send it                  
to other people.                

709
00:31:21,380 --> 00:31:23,580
But then, when you run into     
a problem, of some sort, and    

710
00:31:23,649 --> 00:31:26,616
you don't know how to           
undo that problem,              

711
00:31:26,685 --> 00:31:28,418
It's really hard to figure out  
what's going on if you don't    

712
00:31:28,487 --> 00:31:29,619
know how to Git                 
actually stores things.         

713
00:31:29,688 --> 00:31:31,087
So it's really necessary        
to go through and               

714
00:31:31,156 --> 00:31:34,691
read something like this book   
to understand how Git works.    

715
00:31:34,759 --> 00:31:36,059
And then if you don't           
have a GitHub account,          

716
00:31:36,128 --> 00:31:37,660
go to github.com and            

717
00:31:37,729 --> 00:31:39,396
immediately create              
an account and                  

718
00:31:39,464 --> 00:31:43,433
start creating your repository  
and learning all the commands   

719
00:31:43,502 --> 00:31:45,135
that are better explained       
to you inside this book.        

720
00:31:45,203 --> 00:31:46,236
I highly recommend that.        

721
00:31:49,241 --> 00:31:50,107
in particular,                  

722
00:31:53,044 --> 00:31:58,782
So I'll do file, new project,   
I'll create a single view       

723
00:31:58,851 --> 00:32:04,754
app,I'll call it test, And      
then you'll see that when I'm   

724
00:32:04,823 --> 00:32:06,989
actually creating the project,  
I'll put in my desktop here.    

725
00:32:07,058 --> 00:32:09,025
It actually has a source        
control option for              

726
00:32:09,094 --> 00:32:10,360
creating a Git repository.      

727
00:32:10,428 --> 00:32:12,862
So actually, when you check     
this it'll, it'll put your      

728
00:32:12,931 --> 00:32:15,065
project with a .git file        
in the actual directory.        

729
00:32:15,133 --> 00:32:16,899
And then you can push           
that online to GitHub.          

730
00:32:16,968 --> 00:32:17,968
So it'll do that                
automatically so                

731
00:32:18,037 --> 00:32:18,769
you don't need to               
do it manually.                 

732
00:32:22,140 --> 00:32:23,273
Any other questions?            

733
00:32:25,110 --> 00:32:25,609
No.                             

734
00:32:27,045 --> 00:32:27,644
talk to me afterwards.          

735
00:32:29,180 --> 00:32:31,114
Thank you all.                  

736
00:32:31,182 --> 00:32:35,352
>> For more please visit        
us at stanford.edu.