1
00:00:04,720 --> 00:00:06,970
So now that we've got the layout change

2
00:00:06,970 --> 00:00:09,549
to include our extra button, it's time to

3
00:00:09,549 --> 00:00:11,260
write the code to make the button work.

4
00:00:11,260 --> 00:00:13,809
Now remember that the solution I'm going

5
00:00:13,809 --> 00:00:15,940
to show you is only one solution, so if

6
00:00:15,940 --> 00:00:17,710
your solution works then that's fine

7
00:00:17,710 --> 00:00:20,110
and you've completed the challenge. So

8
00:00:20,110 --> 00:00:21,730
what I'm going to do first is start by

9
00:00:21,730 --> 00:00:23,530
deleting all the commented out code from

10
00:00:23,530 --> 00:00:25,540
a few videos ago. So I'm going to open my

11
00:00:25,540 --> 00:00:27,760
project pane. I'm going to come down to

12
00:00:27,760 --> 00:00:29,800
our MainActivity, and I'm going to

13
00:00:29,800 --> 00:00:31,450
delete all this code, as I mentioned,

14
00:00:31,450 --> 00:00:33,550
that has been commented out. Now I don't

15
00:00:33,550 --> 00:00:36,280
need to delete the imports, but depending

16
00:00:36,280 --> 00:00:38,499
how you've configured Android Studio, you

17
00:00:38,499 --> 00:00:40,659
might have two import lines here, that are

18
00:00:40,659 --> 00:00:42,579
now showing as unused - are sort of greyed

19
00:00:42,579 --> 00:00:44,829
out. So if that's the case, they've probably

20
00:00:44,829 --> 00:00:46,569
been commented out if you've followed, been

21
00:00:46,569 --> 00:00:48,460
following a previous video, so delete

22
00:00:48,460 --> 00:00:50,710
those now. But in my case, because I've

23
00:00:50,710 --> 00:00:52,030
configured Android Studio to

24
00:00:52,030 --> 00:00:54,460
automatically remove unused imports, I

25
00:00:54,460 --> 00:00:56,409
don't need to do anything there. But I'm

26
00:00:56,409 --> 00:00:57,850
going to go ahead and delete this block

27
00:00:57,850 --> 00:00:59,499
over here, that's been, that I've commented out;

28
00:00:59,499 --> 00:01:03,370
the three private definitions Then also

29
00:01:03,370 --> 00:01:05,830
down here, this block of code, which we

30
00:01:05,830 --> 00:01:07,690
discussed the reasons why we don't need

31
00:01:07,690 --> 00:01:09,610
that anymore in the previous video, a few

32
00:01:09,610 --> 00:01:12,040
videos ago. I'm gonna delete that as well,

33
00:01:12,040 --> 00:01:15,670
and just clear up some empty lines there

34
00:01:15,670 --> 00:01:18,460
as well. Alright, so you may have decided

35
00:01:18,460 --> 00:01:20,110
to change the listener for the operator

36
00:01:20,110 --> 00:01:22,420
button, and include the Neg button as

37
00:01:22,420 --> 00:01:24,850
just another operator. For my solution,

38
00:01:24,850 --> 00:01:26,320
though, I decided to create a new

39
00:01:26,320 --> 00:01:28,930
listener, in the same way as we used in

40
00:01:28,930 --> 00:01:31,150
the last section. So what I'm going to do

41
00:01:31,150 --> 00:01:33,250
is add that to the end of the onCreate

42
00:01:33,250 --> 00:01:37,050
method, right down here down the bottom -

43
00:01:37,050 --> 00:01:40,480
basically, here on line 58. So I'm going

44
00:01:40,480 --> 00:01:45,940
to type buttonNeg.set

45
00:01:45,940 --> 00:01:47,010
OnClickListener,

46
00:01:47,010 --> 00:01:50,740
and setOnClickListener

47
00:01:50,740 --> 00:01:53,470
needs the code. So we're going to start

48
00:01:53,470 --> 00:01:58,620
with a left curly brace view and an arrow.

49
00:01:58,620 --> 00:02:02,890
Then on the next line, val value is equal

50
00:02:02,890 --> 00:02:08,639
to a newNumber.text.toString.

51
00:02:08,639 --> 00:02:10,720
Then we're going to do a test here to see

52
00:02:10,720 --> 00:02:15,550
whether it's empty, so if value dot

53
00:02:15,550 --> 00:02:16,870
isEmpty.

54
00:02:16,870 --> 00:02:19,660
If it is empty, then we're going to open a code

55
00:02:19,660 --> 00:02:21,670
block and we're going to set the new

56
00:02:21,670 --> 00:02:25,569
Number, or set number, the edittext, dot

57
00:02:25,569 --> 00:02:28,690
setText parentheses, and we're going to

58
00:02:28,690 --> 00:02:30,430
set that to the minus sign - the

59
00:02:30,430 --> 00:02:33,910
negative sign. Otherwise, we're going to

60
00:02:33,910 --> 00:02:35,799
do some more processing, so we're gonna

61
00:02:35,799 --> 00:02:37,450
have an else block there. And we're going to

62
00:02:37,450 --> 00:02:40,780
start the else block with a try, and

63
00:02:40,780 --> 00:02:45,069
we're going to catch e : and it's going

64
00:02:45,069 --> 00:02:48,340
to be a NumberFormatException, Number

65
00:02:48,340 --> 00:02:52,599
FormatException. And what we're trying

66
00:02:52,599 --> 00:02:54,760
to do here is, we're going to put a

67
00:02:54,760 --> 00:02:55,959
comment here, indicating what would have

68
00:02:55,959 --> 00:02:57,430
happened for a Number Format Exception.

69
00:02:57,430 --> 00:03:00,420
So in in this case, the new number was

70
00:03:00,420 --> 00:03:05,019
set to that already, or a period. So clear

71
00:03:05,019 --> 00:03:09,610
it, if that's the case; newNumber.set

72
00:03:09,610 --> 00:03:11,860
Text parentheses and two double quotes,

73
00:03:11,860 --> 00:03:13,840
just to an empty string. So that's what

74
00:03:13,840 --> 00:03:15,760
happened if the newNumber Format

75
00:03:15,760 --> 00:03:18,549
Exception is thrown, but assuming it's not

76
00:03:18,549 --> 00:03:20,170
thrown, we want to add some code there

77
00:03:20,170 --> 00:03:22,870
to process the number accordingly. So

78
00:03:22,870 --> 00:03:27,040
we're gonna put var doubleValue is

79
00:03:27,040 --> 00:03:31,870
equal to value.toDouble. Then we're

80
00:03:31,870 --> 00:03:35,889
gonna type doubleValue star equals minus

81
00:03:35,889 --> 00:03:37,420
1, so we're multiplying the value by

82
00:03:37,420 --> 00:03:39,840
negative 1. Then we're gonna type newNumber

83
00:03:39,840 --> 00:03:48,000
dot setText doubleValue.toString,

84
00:03:48,000 --> 00:03:50,200
so converting it back to a string so

85
00:03:50,200 --> 00:03:52,780
that we can set the EditText back with

86
00:03:52,780 --> 00:03:55,450
a value - and that should, effectively, be

87
00:03:55,450 --> 00:03:57,400
it. So I've set the onClickListener,

88
00:03:57,400 --> 00:03:59,079
basically, in the same way as we did for

89
00:03:59,079 --> 00:04:01,030
the Button Click Counter, using a lambda.

90
00:04:01,030 --> 00:04:03,579
Now, no other buttons will be using this

91
00:04:03,579 --> 00:04:05,470
listener, so there's no need to create a

92
00:04:05,470 --> 00:04:07,690
named instance, but there's no problem if

93
00:04:07,690 --> 00:04:09,910
you have in your solution. And we'll

94
00:04:09,910 --> 00:04:11,560
probably get a warning from Android

95
00:04:11,560 --> 00:04:13,690
Studio, because one of our layouts

96
00:04:13,690 --> 00:04:16,029
doesn't have a buttonNeg. So if you see

97
00:04:16,029 --> 00:04:17,160
that, don't worry too much about that.

98
00:04:17,160 --> 00:04:22,990
And come over here and have a look, and I've

99
00:04:22,990 --> 00:04:24,880
got a semicolon there from my Java days, so

100
00:04:24,880 --> 00:04:26,169
let me delete that, because it's warning

101
00:04:26,169 --> 00:04:27,909
us about that - which you don't need

102
00:04:27,909 --> 00:04:29,320
because, of course, this is Kotlin and not

103
00:04:29,320 --> 00:04:30,249
Java.

104
00:04:30,249 --> 00:04:32,199
And this is the other one I was talking

105
00:04:32,199 --> 00:04:34,149
about; The resource is missing in some of

106
00:04:34,149 --> 00:04:36,129
layout versions. Parameter view is never

107
00:04:36,129 --> 00:04:37,899
used, and it's talking about the fact here,

108
00:04:37,899 --> 00:04:40,929
that we don't, basically, don't have a

109
00:04:40,929 --> 00:04:43,539
buttonNeg button on both our layouts

110
00:04:43,539 --> 00:04:44,709
because, of course, we've only, at the

111
00:04:44,709 --> 00:04:47,769
moment, updated the landscape version. So

112
00:04:47,769 --> 00:04:50,559
the code itself is pretty simple. If the

113
00:04:50,559 --> 00:04:52,689
text in the widget is empty, then we're

114
00:04:52,689 --> 00:04:54,279
setting it to the minus character and

115
00:04:54,279 --> 00:04:56,529
we're done - that's this code up here, on

116
00:04:56,529 --> 00:04:59,499
line 61. Now the four, the other digit

117
00:04:59,499 --> 00:05:01,119
buttons will add their digits after the

118
00:05:01,119 --> 00:05:03,039
minus, so negative numbers can be

119
00:05:03,039 --> 00:05:05,829
entered. However, if the input text isn't

120
00:05:05,829 --> 00:05:07,779
blank, we go into the else code block.

121
00:05:07,779 --> 00:05:10,209
The code then tries to negate any

122
00:05:10,209 --> 00:05:12,249
number that may have been typed into the

123
00:05:12,249 --> 00:05:14,919
widget. Now if that works, the number is

124
00:05:14,919 --> 00:05:17,019
multiplied by negative 1 to negate it,

125
00:05:17,019 --> 00:05:20,559
here on line 65. Then the widget is

126
00:05:20,559 --> 00:05:22,929
updated with the new value. So positive

127
00:05:22,929 --> 00:05:24,729
numbers in that scenario become negative,

128
00:05:24,729 --> 00:05:27,099
and negative numbers become positive, and

129
00:05:27,099 --> 00:05:29,289
that's exactly what we want here. If

130
00:05:29,289 --> 00:05:31,539
however, there wasn't a valid number, then

131
00:05:31,539 --> 00:05:32,559
that's going to be picked up by the

132
00:05:32,559 --> 00:05:34,599
try/catch block. Now we've already

133
00:05:34,599 --> 00:05:36,669
checked for an empty string, and we're

134
00:05:36,669 --> 00:05:38,019
actually setting the text to a minus

135
00:05:38,019 --> 00:05:40,119
sign if that is the case. So we don't

136
00:05:40,119 --> 00:05:41,259
need to check for that again, in the

137
00:05:41,259 --> 00:05:43,389
catch block. So the only other values

138
00:05:43,389 --> 00:05:44,919
that could cause the catch block to be

139
00:05:44,919 --> 00:05:47,139
entered, are the minus symbol by itself,

140
00:05:47,139 --> 00:05:49,059
if that's been entered, or a decimal

141
00:05:49,059 --> 00:05:52,599
point by itself, or a minus decimal. So

142
00:05:52,599 --> 00:05:53,679
all we really have to do is clear the

143
00:05:53,679 --> 00:05:58,059
text in the widget, in that scenario. So

144
00:05:58,059 --> 00:06:00,189
that's it - the app should still work but

145
00:06:00,189 --> 00:06:02,829
I do have to be careful now, how I test it

146
00:06:02,829 --> 00:06:05,079
at this stage though. 

147
00:06:05,079 --> 00:06:07,629
Remember that we haven't modified the

148
00:06:07,629 --> 00:06:10,509
portrait layout yet, so the layout

149
00:06:10,509 --> 00:06:12,610
won't have a buttonNeg, and the code

150
00:06:12,610 --> 00:06:14,669
will crash if I run it in portrait mode. So 

151
00:06:14,669 --> 00:06:18,459
I'm going to start the emulator up. I'm

152
00:06:18,459 --> 00:06:21,129
going to run the app, and I'm going to

153
00:06:21,129 --> 00:06:22,629
switch to landscape before doing

154
00:06:22,629 --> 00:06:23,769
anything else, just to make sure it

155
00:06:23,769 --> 00:06:24,999
doesn't crash - and that's probably too

156
00:06:24,999 --> 00:06:27,999
slow to do that now, but I'll try. So I'll

157
00:06:27,999 --> 00:06:29,739
switch to landscape, basically, to avoid

158
00:06:29,739 --> 00:06:31,329
the portrait code from running, and

159
00:06:31,329 --> 00:06:33,759
luckily the program is still compiling,

160
00:06:33,759 --> 00:06:40,190
so I'll just wait and speed this up.

161
00:06:40,190 --> 00:06:42,150
Okay, so you can see the app's running.

162
00:06:42,150 --> 00:06:43,620
Because we're in landscape mode, we

163
00:06:43,620 --> 00:06:45,510
didn't crash, and we can see our neg

164
00:06:45,510 --> 00:06:48,660
Button over here. So let's see whether it

165
00:06:48,660 --> 00:06:52,830
works. I'm going to start by typing 58 x

166
00:06:52,830 --> 00:07:06,030
9, pressing neg, + 22 / neg, and the

167
00:07:06,030 --> 00:07:12,510
negative sign there, 5 equals. So

168
00:07:12,510 --> 00:07:14,100
basically, we end up with the value of

169
00:07:14,100 --> 00:07:17,430
100, which is correct in this case. So

170
00:07:17,430 --> 00:07:18,990
basically, you saw that it successfully

171
00:07:18,990 --> 00:07:21,390
negates an existing number 9, and also

172
00:07:21,390 --> 00:07:23,670
allowed for a negative number - negative 5 -

173
00:07:23,670 --> 00:07:25,830
to be entered. Now of course, if I go trying

174
00:07:25,830 --> 00:07:28,650
to go back now to portrait mode, we're

175
00:07:28,650 --> 00:07:30,030
going to get a crash, as we see straight

176
00:07:30,030 --> 00:07:31,440
away, and it said, actually, a

177
00:07:31,440 --> 00:07:32,880
NullPointerException, if we have a look

178
00:07:32,880 --> 00:07:40,100
in logcat; a NullPointerException,

179
00:07:40,100 --> 00:07:42,390
attempting to evoke virtual method

180
00:07:42,390 --> 00:07:43,830
for the Button.set

181
00:07:43,830 --> 00:07:44,550
OnClickListener.

182
00:07:44,550 --> 00:07:47,760
And that is, of course, because we haven't

183
00:07:47,760 --> 00:07:49,830
added the button to the portrait layout

184
00:07:49,830 --> 00:07:52,650
yet. Now sometimes you have to create

185
00:07:52,650 --> 00:07:54,780
different layouts, so that your app looks

186
00:07:54,780 --> 00:07:57,300
ok at different screen sizes. Doing that

187
00:07:57,300 --> 00:07:59,160
does create extra work because you have

188
00:07:59,160 --> 00:08:01,950
to maintain more than one layout. Now you

189
00:08:01,950 --> 00:08:03,510
can test the app before modifying all

190
00:08:03,510 --> 00:08:05,760
the layouts, just like I did here, to make

191
00:08:05,760 --> 00:08:07,680
sure it all works, before putting in the

192
00:08:07,680 --> 00:08:10,950
effort to modify both layouts. Just be

193
00:08:10,950 --> 00:08:12,570
careful to set your emulator into the

194
00:08:12,570 --> 00:08:14,580
working mode before running the app, and

195
00:08:14,580 --> 00:08:16,500
don't cause the other layout to be used,

196
00:08:16,500 --> 00:08:18,000
until you've gone ahead and created, or

197
00:08:18,000 --> 00:08:20,250
modified it. Alright, so I'll end this

198
00:08:20,250 --> 00:08:21,840
video here. In the next one, we'll make

199
00:08:21,840 --> 00:08:24,090
changes to the portrait layout, and add

200
00:08:24,090 --> 00:08:25,680
the negButton to that portrait layout

201
00:08:25,680 --> 00:08:27,810
to get it working, and we'll then have the

202
00:08:27,810 --> 00:08:31,790
app completed. See you in the next video.