1
00:00:00,170 --> 00:00:04,220
We're updating our model but
now we need to update our view as well,

2
00:00:04,220 --> 00:00:08,230
which can be a little bit
tricky especially with Android.

3
00:00:08,230 --> 00:00:08,990
We'll need to wait for

4
00:00:08,990 --> 00:00:12,890
the activities on create method
before we can create the view.

5
00:00:12,890 --> 00:00:16,940
So we aren't going to be able to
initialize our view right from the get go.

6
00:00:16,940 --> 00:00:20,340
To remedy this let's create a property for
our view and

7
00:00:20,340 --> 00:00:23,450
then once our view has been created,
we'll call a function and

8
00:00:23,450 --> 00:00:26,920
our game presenter class to
populate our view property.

9
00:00:26,920 --> 00:00:31,200
First let's make a property for our view
and since we're going to be setting its

10
00:00:31,200 --> 00:00:35,990
value later with a function, we'll need
to declare this property as mutable.

11
00:00:35,990 --> 00:00:41,850
At the the top of our class, let's type
var view, give it a type of GameView.

12
00:00:44,810 --> 00:00:48,330
And then, since we don't have
anything to set it to yet, and

13
00:00:48,330 --> 00:00:53,800
we have to set it to something, let's
set it to null, which gives us an error,

14
00:00:53,800 --> 00:00:58,690
null cannot be a value of
non null type GameView.

15
00:00:58,690 --> 00:01:00,618
Okay, so what does that mean?

16
00:01:00,618 --> 00:01:05,560
Well in Kotlin if you want an object to
be able to equal null you need to add

17
00:01:05,560 --> 00:01:11,030
a question mark after the datatype, this
is one of my favorite parts about Kotlin.

18
00:01:11,030 --> 00:01:15,200
It's not much but when you have to take
the time to think about whether a property

19
00:01:15,200 --> 00:01:20,110
can be null or not I find that
I end up writing better code.

20
00:01:20,110 --> 00:01:23,130
And definitely have a lot
fewer null pointer exceptions.

21
00:01:23,130 --> 00:01:25,980
Anyway, now that we've got our
view property let's create

22
00:01:25,980 --> 00:01:27,470
a function to populate it.

23
00:01:27,470 --> 00:01:29,935
And let's name it setGameView.

24
00:01:30,950 --> 00:01:35,770
Let's make it taken the gameview
as a parameter and then

25
00:01:35,770 --> 00:01:40,860
inside this function let's set our view
property equal to our gameView parameter.

26
00:01:42,510 --> 00:01:46,370
And now that we've got access to our view
let's update it at the bottom of our

27
00:01:46,370 --> 00:01:51,360
onDeckTap function, view.update and

28
00:01:51,360 --> 00:01:54,608
pass in our GameModel.

29
00:01:54,608 --> 00:01:57,729
Nice, but what's this are all about?

30
00:01:57,729 --> 00:01:58,626
Only safe or

31
00:01:58,626 --> 00:02:04,203
non null asserted calls are allowed on
a noble receiver of type game view.

32
00:02:04,203 --> 00:02:08,757
This is just another way that Kotlin makes
sure we really know what we're doing

33
00:02:08,757 --> 00:02:10,277
when dealing with nulls.

34
00:02:10,277 --> 00:02:14,160
You see Kotlin knows our
view property can be null.

35
00:02:15,600 --> 00:02:19,681
Kotlin also knows that it's
possible that we're calling this

36
00:02:19,681 --> 00:02:24,980
update function on a null object,
which makes Kotlin very unhappy.

37
00:02:24,980 --> 00:02:28,420
To solve this issue Kotlin
gives us two options.

38
00:02:28,420 --> 00:02:31,170
We can add a question
mark before the call, and

39
00:02:31,170 --> 00:02:35,590
now if our view is null,
we won't call the update function and

40
00:02:35,590 --> 00:02:41,430
this whole line will just return null or
on the other hand

41
00:02:41,430 --> 00:02:46,100
if our view is not null, then it will call
the update function just like we want.

42
00:02:46,100 --> 00:02:50,470
The other way we can handle this
is to use two exclamation points.

43
00:02:50,470 --> 00:02:53,510
When we precede a call with
two exclamation points,

44
00:02:53,510 --> 00:02:57,970
we are promising Kotlin that whatever
is before the exclamation points is not

45
00:02:57,970 --> 00:03:02,910
going to be null and if we promise that
something isn't going to be null and

46
00:03:02,910 --> 00:03:06,660
then it is null we'll get
a null pointer exception.

47
00:03:06,660 --> 00:03:10,410
So just to be on the safe side
let's go back to using a safe call

48
00:03:10,410 --> 00:03:11,631
by adding in our question mark.

49
00:03:14,110 --> 00:03:15,300
Great work.

50
00:03:15,300 --> 00:03:17,770
Now that we're done with
the onDeckTap function

51
00:03:17,770 --> 00:03:20,460
let's move on to our onWasteTap function.

52
00:03:20,460 --> 00:03:24,410
Let's declare the function fun onWasteTap.

53
00:03:25,480 --> 00:03:29,450
And then inside, let's update the model,

54
00:03:29,450 --> 00:03:34,076
GameModel.onWasteTap and
then update the view.

55
00:03:34,076 --> 00:03:36,027
View?

56
00:03:36,027 --> 00:03:40,246
To make sure that we null for
the whole statement if our view is null,

57
00:03:40,246 --> 00:03:42,550
.update and pass in our GameModel.

58
00:03:43,780 --> 00:03:44,650
And actually,

59
00:03:44,650 --> 00:03:49,360
wouldn't it be nice if we didn't have
to pass in the GameModel each time?

60
00:03:49,360 --> 00:03:51,840
After all, it is a singleton.

61
00:03:51,840 --> 00:03:56,240
Let's head over to our GameView interface
and see if we can't add our GameModel

62
00:03:56,240 --> 00:04:01,167
instance as a default value, = GameModel.

63
00:04:02,660 --> 00:04:08,310
Now back in our game presenter we can
stop passing in our model as a parameter.

64
00:04:10,310 --> 00:04:14,890
Nice, getting back to our two remaining
functions to give us a head start.

65
00:04:14,890 --> 00:04:17,069
Let's just copy them in
from our game model class.

66
00:04:29,797 --> 00:04:37,392
Then let's delete the function bodies, And

67
00:04:37,392 --> 00:04:41,773
starting with onFoundationTap
we need to first call

68
00:04:41,773 --> 00:04:47,758
GameModel.onFoundationTap, and
pass along the foundationIndex.

69
00:04:50,062 --> 00:04:51,813
Then we need to update our view.

70
00:04:53,707 --> 00:05:00,115
Finally, for our on tableau tap function,
we need to call GameModel.onTableauTap.

71
00:05:01,640 --> 00:05:07,650
Pass in our TableauIndex and
our cardIndex and then update our view.

72
00:05:10,740 --> 00:05:13,880
All right, we've completely
finished our game of solitaire.

73
00:05:13,880 --> 00:05:17,600
And while I know we won't be getting
to the UI part until the next course,

74
00:05:17,600 --> 00:05:21,480
that doesn't mean we can't see some
sweet solitaire action in this course.

75
00:05:21,480 --> 00:05:22,560
In the next stage,

76
00:05:22,560 --> 00:05:25,340
we'll look into creating a test to
make sure that our game is working.