1
00:00:00,350 --> 00:00:03,030
We've just finished updating
our activities layout

2
00:00:03,030 --> 00:00:05,960
to have a placeholder view group for
our fragments.

3
00:00:05,960 --> 00:00:07,990
Now let's head over to MainActivity and

4
00:00:07,990 --> 00:00:10,520
use this placeholder to
display our new list fragment.

5
00:00:11,820 --> 00:00:15,420
Before we can display our list fragment,
it needs to exist.

6
00:00:15,420 --> 00:00:19,010
Let's create a new list fragment variable
at the bottom of the onCreate method.

7
00:00:20,210 --> 00:00:21,230
List fragment.

8
00:00:21,230 --> 00:00:24,910
Let's call it fragment = new ListFragment.

9
00:00:26,710 --> 00:00:28,420
Now that we've got our ListFragment,

10
00:00:28,420 --> 00:00:32,760
all we need to do is add this ListFragment
to our place holder view group.

11
00:00:32,760 --> 00:00:36,970
Let's start by creating a new fragment
manager variable named, fragment manager.

12
00:00:38,140 --> 00:00:39,570
Fragment manager.

13
00:00:39,570 --> 00:00:42,740
And make sure you're getting the one
from the Android.app package and

14
00:00:42,740 --> 00:00:44,180
not the one from the support package.

15
00:00:45,680 --> 00:00:50,330
Name it FragmentManager, and
then let's set it = getFragmentManager.

16
00:00:51,645 --> 00:00:54,297
[NOISE] The fragment
manager is an interface for

17
00:00:54,297 --> 00:00:56,275
interacting with our fragments.

18
00:00:56,275 --> 00:01:00,418
It helps us keep track of our fragments,
let's us manage the back stack of our

19
00:01:00,418 --> 00:01:04,310
fragments, and gives us access to
the fragment transactions A.P.I.

20
00:01:04,310 --> 00:01:08,430
which allows us to do things like add or
remove fragments.

21
00:01:08,430 --> 00:01:13,520
On the next line, let's create a new
fragment transaction variable and

22
00:01:13,520 --> 00:01:15,055
let's call it FragmentTransaction.

23
00:01:16,780 --> 00:01:24,018
Then let's set it =
fragmentManager.begintransaction.

24
00:01:24,018 --> 00:01:26,080
Then we see a warning

25
00:01:27,280 --> 00:01:30,640
that this transaction should be
completed with the commit call.

26
00:01:31,650 --> 00:01:33,280
So let's add two lines below here.

27
00:01:35,820 --> 00:01:43,140
And add that commit call
fragmentTransaction.commit.

28
00:01:43,140 --> 00:01:46,390
Fragment transactions are a lot
like shared preferences.

29
00:01:46,390 --> 00:01:49,610
Any changes won't be made permanent
until there's a call to commit.

30
00:01:50,770 --> 00:01:52,640
Back up on the line we skipped,

31
00:01:52,640 --> 00:01:55,906
let's finally add our list fragment
to our placeholder view group.

32
00:01:55,906 --> 00:02:00,816
Let's type fragmentTransaction.add,

33
00:02:00,816 --> 00:02:05,997
and for
the first parameter let's pass in our

34
00:02:05,997 --> 00:02:11,466
placeholder as the ID, R.id.placeholder.

35
00:02:13,070 --> 00:02:15,450
And for the second parameter,
let's pass in our fragment.

36
00:02:17,510 --> 00:02:18,240
Awesome.

37
00:02:18,240 --> 00:02:20,600
Now let's test the app and
see our fragment in action.

38
00:02:25,100 --> 00:02:25,890
Bummer.

39
00:02:25,890 --> 00:02:27,270
An error.

40
00:02:27,270 --> 00:02:27,980
Over in the log.

41
00:02:36,095 --> 00:02:39,360
It looks like we've got
an illegal state exception.

42
00:02:39,360 --> 00:02:42,010
The specified child already has a parent.

43
00:02:42,010 --> 00:02:46,190
You must call removeView on
the child's parent first.

44
00:02:46,190 --> 00:02:47,890
Okay, so where did this error occur?

45
00:02:51,700 --> 00:02:54,680
Nowhere, great.

46
00:02:54,680 --> 00:02:59,025
This might be a good time to talk about
why fragments can sometimes get a bad rap.

47
00:03:00,560 --> 00:03:02,710
There's just a lot of stuff to handle.

48
00:03:02,710 --> 00:03:04,250
On top of fragment managers and

49
00:03:04,250 --> 00:03:08,980
fragment transactions, fragments
themselves also have a life cycle.

50
00:03:08,980 --> 00:03:11,530
And the interplay between
the fragment life cycle and

51
00:03:11,530 --> 00:03:16,120
the activity life cycle can sometimes
leave you scratching your head, like here.

52
00:03:17,440 --> 00:03:18,720
To fix this error.

53
00:03:18,720 --> 00:03:21,020
we need to head over to
our list fragment class.

54
00:03:22,770 --> 00:03:26,630
Let's add a third parameter to
the inflate method and pass in false.

55
00:03:29,590 --> 00:03:31,620
The third parameter determines whether or

56
00:03:31,620 --> 00:03:36,770
not we attach this view to the view
group provided as the second parameter.

57
00:03:36,770 --> 00:03:39,360
It might seem weird that
we would set this to false

58
00:03:39,360 --> 00:03:41,910
when we actually do want to
attach to that view group.

59
00:03:43,450 --> 00:03:46,080
But when on Create view returns,

60
00:03:46,080 --> 00:03:50,050
our view will be automatically added to
the container view group by the system.

61
00:03:51,260 --> 00:03:55,360
So if we don't set this to false,
it'll be added twice and

62
00:03:55,360 --> 00:03:56,990
will get the error we saw earlier.

63
00:03:58,830 --> 00:04:01,249
Now that that's fixed,
let's run the app again.

64
00:04:06,128 --> 00:04:07,750
And there's our fragment.

65
00:04:07,750 --> 00:04:08,990
Nice.

66
00:04:08,990 --> 00:04:13,230
In the next video, we'll start making our
list fragment look a bit more list like.