1
00:00:05,550 --> 00:00:10,800
Alright, so it's time to start creating our app to download the flickr feed and pass out the information

2
00:00:10,800 --> 00:00:14,420
that we need, so we need to start a new project in Android Studio.

3
00:00:14,420 --> 00:00:23,810
So I'm going to do that, and I'm going to call this one Flickr Browser. The company domain,

4
00:00:23,810 --> 00:00:31,600
I'm going to have learn programming dot Academy as I've done for other videos in this course, and as

5
00:00:31,600 --> 00:00:35,980
usual tick the box to include Kotlin support if you're using Kotlin, and leave it

6
00:00:35,980 --> 00:00:40,330
unticked if you're using Java.

7
00:00:40,330 --> 00:00:46,210
Click on next, and on this screen we're going to choose API 17 as we normally do,

8
00:00:46,210 --> 00:00:53,730
we've done for other projects in this course, click on next. Now in the template screen here I've currently got

9
00:00:53,730 --> 00:00:55,800
the choices that you can see on screen.

10
00:00:55,800 --> 00:01:00,510
However keep in may that Google do change the templates from time to time, and the options you've got

11
00:01:00,510 --> 00:01:02,550
available may be different.

12
00:01:02,550 --> 00:01:07,560
And as I mentioned in the templates video in section 3, these are just templates that we can add and

13
00:01:07,560 --> 00:01:09,300
remove code as needed.

14
00:01:09,300 --> 00:01:13,830
So it makes sense to choose a template that best fits your application, and there should always be something

15
00:01:13,830 --> 00:01:19,020
like the empty activity, that'll create a project with very little code filled in for you.

16
00:01:19,020 --> 00:01:24,960
Now this app we're creating is going to use a menu, but we won't be using the floating action button because

17
00:01:24,960 --> 00:01:31,410
you can see at the bottom of the basic activity template, this one here, basic activity has both a menu and

18
00:01:31,410 --> 00:01:37,580
a fab, a floating action button, and you can see the menu at the top half here of the templates image.

19
00:01:37,580 --> 00:01:42,810
Now I don't want both, but it's easier to remove code than go to the trouble of adding code for the menu,

20
00:01:42,810 --> 00:01:46,590
back in. So basic activity is the one that we're going to use here.

21
00:01:46,590 --> 00:01:50,970
Once again if you have different options in your version of Android Studio when you come to watch this

22
00:01:50,970 --> 00:01:56,980
video, choose the simplest available template that includes a menu. So I'm going to click on next now that I've chosen

23
00:01:56,980 --> 00:02:05,300
basic activity. I'm going to leave all these names at the moment as the default. While we're creating this

24
00:02:05,300 --> 00:02:11,570
app I'm going to show you how to manually rename and change things anyway. So with that done I'm going to click on finish. We're going to wait

25
00:02:11,570 --> 00:02:20,900
while Android Studio creates the project for us.

26
00:02:20,900 --> 00:02:25,760
Alright so you can see we've just about finished, and our default application's being created,

27
00:02:25,760 --> 00:02:33,170
and we should see two created layouts here, and I'll just expand up here so we can have a look, look in the res folder.

28
00:02:33,170 --> 00:02:38,750
And we just need to give it a little bit longer to complete, and then we'll be able to see. Alright there we go. I can

29
00:02:38,750 --> 00:02:40,700
see now that in our layout folder,

30
00:02:40,700 --> 00:02:46,580
we've got activity main and content main dot xml, and we saw those in the template videos.

31
00:02:46,580 --> 00:02:48,770
Now Google may decide to change that,

32
00:02:48,770 --> 00:02:52,370
so if you only got a single layout xml file created that's fine.

33
00:02:52,370 --> 00:02:57,410
Just make your changes in that one. OK now I want to add logging code to our app.

34
00:02:57,410 --> 00:03:02,120
I mentioned this in the button counter app, in that section of the course, when we looked at the activity

35
00:03:02,120 --> 00:03:05,850
life cycle, but I'm going to go over it briefly again here.

36
00:03:05,850 --> 00:03:11,060
Logging when your methods start and end is one of the most useful techniques you can use when trying

37
00:03:11,060 --> 00:03:14,540
to understand how the Android framework operates.

38
00:03:14,540 --> 00:03:19,030
So I'm going to leave the user interface, the creation of that, until later.

39
00:03:19,030 --> 00:03:22,400
We're going to start by downloading the data and then parsing it.

40
00:03:22,400 --> 00:03:26,810
So we're going to be writing a lot of output to the log cat, so that we can check what's happening and

41
00:03:26,810 --> 00:03:28,760
see that things are working.

42
00:03:28,760 --> 00:03:35,420
Now this app will also be using an async task to perform the download on a separate thread. So that stops

43
00:03:35,420 --> 00:03:41,400
the user interface from appearing to hang when a potentially long running task is going on.

44
00:03:41,400 --> 00:03:46,400
Now it's a good idea to do things like downloading or reading lots of data from a file or database in

45
00:03:46,400 --> 00:03:47,930
a separate thread.

46
00:03:47,930 --> 00:03:54,890
In fact the http class, which we're going to use, will give an error if we try to download on the main user

47
00:03:54,890 --> 00:03:56,210
interface thread.

48
00:03:56,210 --> 00:04:01,280
Now messaging threads can be tricky but the async task does all the hard work for us.

49
00:04:01,280 --> 00:04:06,290
So we're going to take a similar approach to the top 10 downloader app, but I'm going to be doing things

50
00:04:06,290 --> 00:04:12,200
slightly differently when we come to use the data downloaded by the async task.

51
00:04:12,200 --> 00:04:16,519
Now as I mentioned in the introduction, the app's also going to be using an adapter

52
00:04:16,519 --> 00:04:21,529
when we come to display the data. Now the way all the various classes work together can take a while

53
00:04:21,529 --> 00:04:22,760
to understand,

54
00:04:22,760 --> 00:04:28,100
so what I'm going to do is log a message each time a method's called. Now the messages in the log will

55
00:04:28,100 --> 00:04:33,080
then show what methods are being called, and when. This allows us to see what's happening,

56
00:04:33,080 --> 00:04:38,900
and the order that things are being called. Now those log entries will make it much easier to understand

57
00:04:38,900 --> 00:04:40,700
how the app works.

58
00:04:40,700 --> 00:04:44,900
Now up until now we've used a private variable for the log tag.

59
00:04:44,900 --> 00:04:50,820
So I'll start this app by showing you another way to define it, using something called a companion object.

60
00:04:50,820 --> 00:04:57,300
Now Kotlin doesn't have a direct equivalent to Java's static variables but we can create something similar.

61
00:04:57,300 --> 00:05:05,020
Now I'm going to add it to the end of our main activity class, so let's open that up, and down here before the last right

62
00:05:05,020 --> 00:05:11,310
curly brace, I'm going to type companion, object and just press enter there.

63
00:05:11,310 --> 00:05:20,740
OK like so, and then within the companion object we're going to type private const val, TAG in upper case, equals

64
00:05:20,740 --> 00:05:26,070
double quotes MainActivity. So that's our companion object.

65
00:05:26,070 --> 00:05:32,410
And then what we're going to do is come up to our onCreate method up here, and we're going to actually to use that.

66
00:05:32,410 --> 00:05:41,770
So basically on the first line, before the super.OnCreate code, we're going to type Log dot d parentheses TAG

67
00:05:41,770 --> 00:05:53,840
in uppercase, comma space, then onCreate in double quotes, called. OK we're also going to add the same thing, a log

68
00:05:53,840 --> 00:05:58,550
entry to onCreateOptionsMenu and on items, onOptionsItemsSelected.

69
00:05:58,550 --> 00:06:06,740
So I'm going to take a copy of that line, first line of the onCreateOptionsMenu, just put it in there. This time we'll

70
00:06:06,740 --> 00:06:15,730
change it though, so it's onCreateOptionsMenu, and for the onOptionsItemsSelected,

71
00:06:15,730 --> 00:06:31,020
we're going to put a Log.d before the return when, so that's onOptionsItemSelected called, as you can see. OK.

72
00:06:31,020 --> 00:06:35,660
That's a fairly standard debug logging line that we've used a few times now.

73
00:06:35,660 --> 00:06:38,040
So what I'm going to do is run this to make sure that it's working,

74
00:06:38,040 --> 00:06:41,680
so we're going to start the app, and I'm going to start my emulator.

75
00:06:41,680 --> 00:06:53,770
It's not started on this device, so I'll just fast-forward this one starting. OK,

76
00:06:53,770 --> 00:06:55,130
there's our app running, and

77
00:06:55,130 --> 00:07:01,190
if you go back to log cat, we should be able to see that output hopefully, and what I can do to make sure we

78
00:07:01,190 --> 00:07:09,770
can actually filter on main activity, so let's try doing that, and there we go, main activity.

79
00:07:09,770 --> 00:07:14,930
That's enough there, you can see we've got our two options at the moment, onCreate is being called, and on

80
00:07:14,930 --> 00:07:21,340
CreateOptionsMenu has also been called. So what have we done differently, and perhaps more importantly,

81
00:07:21,340 --> 00:07:23,230
why am I showing you this.

82
00:07:23,230 --> 00:07:28,300
Well to answer the second question first, I'm showing you this because you're going to see it being used.

83
00:07:28,300 --> 00:07:33,760
It's the code that'll be generated automatically, when you use Android Studio to convert Java code

84
00:07:33,760 --> 00:07:35,600
to Kotlin for one thing.

85
00:07:35,600 --> 00:07:39,730
Now I'm not going to show you how to convert Java to Kotlin yet, and that's mainly because it's too

86
00:07:39,730 --> 00:07:46,270
easy just do that yet and end up not really writing Kotlin. But you'll see these companion objects

87
00:07:46,270 --> 00:07:50,810
like we've created here, used for things like analog tag.

88
00:07:50,810 --> 00:07:56,900
So it's important to be familiar with code like this, and again this code I'm talking about is the code on line 44.

89
00:07:56,900 --> 00:08:04,040
Now Java has things called static fields, and these belong to the class rather than to the instances

90
00:08:04,040 --> 00:08:07,400
of the class. Now don't worry too much about that.

91
00:08:07,400 --> 00:08:13,490
We're working with Kotlin not Java after all, but one reason for using those static fields is that there's

92
00:08:13,490 --> 00:08:15,920
only one copy created.

93
00:08:15,920 --> 00:08:23,220
Now if we used a normal variable, each instance of main activity would create a new copy of the tag variable.

94
00:08:23,220 --> 00:08:29,100
Now obviously that's not a good use of memory because each copy would contain exactly the same text,

95
00:08:29,100 --> 00:08:34,970
and if we created 1000 instances of main activity, you'd have a thousand variables all with exactly the

96
00:08:34,970 --> 00:08:35,900
same value,

97
00:08:35,900 --> 00:08:41,870
the string main activity, so that's nearly 12K of ram used up, which is a bit of a waste to put it mildly.

98
00:08:41,870 --> 00:08:47,310
So that's one reason for using class variables rather than instance variables.

99
00:08:47,310 --> 00:08:52,610
Now the equivalent way to do that in Kotlin is to use a companion object, and declare tag

100
00:08:52,610 --> 00:08:57,140
in this case, in there. Now unfortunately it's not exactly equivalent.

101
00:08:57,140 --> 00:09:03,740
In fact because we've used const here on line 45, we end up with a tag being placed in line.

102
00:09:03,740 --> 00:09:10,010
So that means the text is copied into our code, every where that we've used the tag variable.

103
00:09:10,010 --> 00:09:14,690
Now that may not make much sense, so I'm going to convert the code to Java to show what's being

104
00:09:14,690 --> 00:09:16,850
produced for us.

105
00:09:16,850 --> 00:09:20,600
Now if you don't know Java, don't worry too much about the code we're about to see.

106
00:09:20,600 --> 00:09:27,190
The point is to show you how our tag variable is really used where the Kotlin program is compiled.

107
00:09:27,190 --> 00:09:32,230
Now converting Kotlin to Java is currently a two step process.

108
00:09:32,230 --> 00:09:39,600
So first thing is the Decompile Kotlin to Java option, this is on the tools Kotlin menu,

109
00:09:39,600 --> 00:09:44,590
Decompile Kotlin to Java, which is currently greyed. So it's basically not available yet,

110
00:09:44,590 --> 00:09:50,720
but what we can do instead, is use the Show Kotlin Bytecode option to see what our Kotlin code compiles

111
00:09:50,720 --> 00:10:02,830
to. So basically, tools, Kotlin, Show Kotlin Bytecode.

112
00:10:02,830 --> 00:10:10,040
If I bring this over a little bit more, you can see all this strange code in the Kotlin Bytecode pane. Now there's very few

113
00:10:10,040 --> 00:10:13,990
people on the planet who can understand this Bytecode.

114
00:10:13,990 --> 00:10:16,190
Now I'm not going to attempt to make sense of it.

115
00:10:16,190 --> 00:10:23,030
It's intended for the JVM to execute, not for humans to read, but what we can do is click the decompile

116
00:10:23,030 --> 00:10:25,960
button to convert it back to Java.

117
00:10:25,960 --> 00:10:33,500
So go go ahead and do that, and I'm going to close this window,

118
00:10:33,500 --> 00:10:37,070
and this is the decompiled version converted back to Java.

119
00:10:37,070 --> 00:10:42,950
Now this might look horrible, but if we scroll down and have a look we can see the Log.d calls

120
00:10:42,950 --> 00:10:49,410
in each of the methods - Log.d again, Log.d and Log.d.

121
00:10:49,410 --> 00:10:56,480
So notice that the string main activity is actually repeated in each of those calls, three times there.

122
00:10:56,480 --> 00:11:03,020
That's what I meant by the tag value being placed in line. Now our attempt to save memory by using

123
00:11:03,020 --> 00:11:06,790
the Kotlin equivalent of a static field hasn't worked out too well. Our

124
00:11:06,790 --> 00:11:15,400
code's duplicating the value of tag, each time we do any logging. OK I'm going to close the decompiled Java tab here, and 

125
00:11:15,400 --> 00:11:21,290
I've already closed the Kotlin Bytecode pane. I'm going to go back to our code now on the screen. So you'll almost

126
00:11:21,290 --> 00:11:26,300
certainly come across code that uses a companion object like we've used here.

127
00:11:26,300 --> 00:11:31,130
But I'm going to suggest that you don't do it in your activities. So just to be clear I'm not saying

128
00:11:31,130 --> 00:11:33,140
that you shouldn't use companion objects.

129
00:11:33,140 --> 00:11:36,440
We're using them in some of our code and they do have their uses.

130
00:11:36,440 --> 00:11:39,110
What I'm saying is that I wouldn't use one here.

131
00:11:39,110 --> 00:11:43,250
Now one reason is, we're only going to have one instance of main activity anyway.

132
00:11:43,250 --> 00:11:48,260
Well now we may create thousands of instances of some classes, such as the feed entry class in our Top

133
00:11:48,260 --> 00:11:53,480
10 downloader. We created an instance of feed entry for each row in the list view.

134
00:11:53,480 --> 00:11:59,390
So we definitely created quite a few of those, but it's very rare for an app to create several instances

135
00:11:59,390 --> 00:12:01,370
of an activity at the same time,

136
00:12:01,370 --> 00:12:06,260
so the benefit of a static field in saving memory doesn't really apply here.

137
00:12:06,260 --> 00:12:11,810
Now if you're comfortable with Java, and want to check the decompiled code again for, after removing const

138
00:12:11,810 --> 00:12:16,070
from line 45, you'll see why that's also not a good option.

139
00:12:16,070 --> 00:12:24,640
So I'm going to comment out our companion object code anyway, rather than deleting it, so it's available for reference.

140
00:12:24,640 --> 00:12:30,560
Now I've covered this now, because it's about now that you probably want to know about the lint boarding

141
00:12:30,560 --> 00:12:32,920
when we declared tag as a normal variable.

142
00:12:32,920 --> 00:12:40,080
So let's just come up here and do that first, right at the top, we're going to do it as the first entry inside the class, so private

143
00:12:40,080 --> 00:12:50,230
val, TAG in uppercase equals, in double quotes MainActivity, and we get a weak warning that private property

144
00:12:50,230 --> 00:12:56,380
tag doesn't match, so come over here, private property name tag doesn't match regex.

145
00:12:56,380 --> 00:13:01,860
Now we're getting that warning because variable names should begin with a lower case letter. Constants

146
00:13:01,860 --> 00:13:05,290
should be in all capitals and we're using tag as a constant,

147
00:13:05,290 --> 00:13:07,360
but we haven't declared it to be one.

148
00:13:07,360 --> 00:13:11,980
We've just seen why we don't want to do that, but it does mean we get this warning.

149
00:13:11,980 --> 00:13:16,720
Now one way to remove this warning is to name tag in lowercase.

150
00:13:16,720 --> 00:13:19,150
That's an option but not something we want to do,

151
00:13:19,150 --> 00:13:23,680
if we're working with XML for example. There's all sorts of examples where we might want to refer

152
00:13:23,680 --> 00:13:29,130
to tags, and using tag in lowercase for our logging would just cause confusion.

153
00:13:29,130 --> 00:13:30,850
Now I don't actually have an answer for this.

154
00:13:30,850 --> 00:13:37,120
The best solution I can think of would be to disable the lint check for this line of code, but unfortunately

155
00:13:37,120 --> 00:13:38,740
that's not possible at the moment.

156
00:13:38,740 --> 00:13:45,510
It is actually worth clicking on TAG, and then come over here and check it on the light bulb options, to see

157
00:13:45,510 --> 00:13:48,540
if there's an option to suppress the warning in the future.

158
00:13:48,540 --> 00:13:50,810
For now I'm just going to live with the warning.

159
00:13:50,810 --> 00:13:55,050
Now that's not ideal but at the moment it's the best option we have available.

160
00:13:55,050 --> 00:14:02,640
OK, so moving. Now as I mentioned previously we don't need the floating action bar code in the onCreate method. So,

161
00:14:02,640 --> 00:14:05,880
that's because we're not using the floating action button in this app.

162
00:14:05,880 --> 00:14:09,580
So I'm going to go ahead and delete that code, that's this code here from fab.setOn

163
00:14:09,580 --> 00:14:18,780
ClickListener, and comment all that out, like so, and the other thing I'm going to do, is actually add a log entry for when the

164
00:14:18,780 --> 00:14:28,380
method ends. So I'm going to do a Log.d after that, parentheses TAG comma double quotes onCreate ends.

165
00:14:28,380 --> 00:14:33,240
So each time this onCreate function is called from now on, we'll see the message "onCreate called"

166
00:14:33,240 --> 00:14:37,650
when the function starts, and "onCreate ends" when it finishes.

167
00:14:37,650 --> 00:14:42,450
Now I'm not going to be including logging like this in every single function, but I will add it to the

168
00:14:42,450 --> 00:14:46,770
interesting ones so that we can see the flow of the program when it runs.

169
00:14:46,770 --> 00:14:50,580
Now Android Studio should also remove the fab imports automatically,

170
00:14:50,580 --> 00:14:56,420
but if it doesn't, they'll appear in grey to show they're not being used. So scroll up to the top and have a look at our imports.

171
00:14:56,420 --> 00:15:03,770
In my case you can see they've actually being removed, and I'll put this back just to show you what I mean.

172
00:15:03,770 --> 00:15:13,650
And we can see how they're added automatically, and if I comment that out again, they're actually removed,

173
00:15:13,650 --> 00:15:18,660
see the snack bar gets removed for us automatically in the imports. Well there's actually three, there's a floating action

174
00:15:18,660 --> 00:15:21,490
button, a snack bar and then the Android.view.view, and

175
00:15:21,490 --> 00:15:27,030
you can see that they've all, they're now no longer showing in the input section.

176
00:15:27,030 --> 00:15:29,280
Alright so this video's got quite long. Our

177
00:15:29,280 --> 00:15:34,200
basic project has been set up, so I'm gonna stop the video here, and in the next video we'll start looking

178
00:15:34,200 --> 00:15:38,180
at downloading our json data. So I'll see you in that next video.