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Well done!
You have completed Build a Simple Android App with Kotlin!
Preview
The last thing we need to do is pick a new background color each time we display a new fact. Try it yourself, then watch this video for my explanation.
Documentation
- RelativeLayout Class Reference
- Color Class Reference - Contains several Color constants you can use
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We're almost done.
0:00
The last thing we need to do
is pick a new background color
0:01
each time we display a new fact.
0:04
Sounds simple enough, right?
0:07
If you're feeling adventurous, why
don't you pause me and try it yourself.
0:08
Then come back and see how I do it.
0:12
Here are the steps you need to do.
0:15
Step one, declare a property with
the data type of RelativeLayout?
0:17
And set it equal to null.
0:22
The format is just like
our other view fields but
0:24
with a different name and data type.
0:26
Step two, set this property in the
onCreate method just like the other views.
0:29
You may need to add an ID to
the RelativeLayout in the layout file.
0:35
Step three, where we set a new fun fact,
0:39
call the setBackgroundColor
method on this new variable.
0:42
Use Color.RED as the parameter.
0:46
All right, did you get it working?
0:51
Let's switch to FunFactsActivity and
start from the top.
0:53
Declare a property with the data
type of RelativeLayout?
0:56
Let's add a new line below our
showFactButton declaration,
1:00
and type private
var_relativeLayout: RelativeLayout?
1:07
And set it equal to null.
1:13
Okay, on to step two.
1:17
Set this property on the onCreate method.
1:19
Let's add a new line below where
we initialized showFactButton.
1:22
And then type relativeLayout
1:26
= findViewById(R.id.).
1:32
And that's right, we haven't give
our relativeLayout and ID yet.
1:38
If we had, we will be be able
to see that ID in this list.
1:42
Let's open of our layout file.
1:46
So Project > res > layout
> activity_fun_facts.xml.
1:48
Let me have the preview and
inside this first RelativeLayout tab,
1:54
let's add an ID property.
1:59
Let's add a line after where
we set the padding and
2:01
type android:id="@+id/relative
" with a lower case r.
2:08
Remember, we could have also set
the ID from the design tab by
2:19
selecting the RelativeLayout
from the component tree and
2:22
then setting the ID on the property pane.
2:25
Looks good, let's go back to our
activity and reference our new ID.
2:28
Let's hit Ctrl+Space,
to bring back up auto complete.
2:34
And then select relativeLayout.
2:40
And finally,
add the cast to relativeLayout.
2:42
So much for step two.
2:45
Next step, step three,
where we set a new fun fact called the set
2:47
background color method on our new
variable using Color.RED as the parameter.
2:51
This is referring to our onClick listener.
2:56
At the bottom,
let's reference our new variable and
2:59
assert that it isn't null,
relativeLayout!!
3:04
Then, using auto complete as our guide,
let's add a dot and type sbc.
3:09
Just typing the first
letter of each word and
3:15
a method is another way to let auto
complete know what we're looking for.
3:17
Let's select
the setBackgroundColor method and
3:22
it takes in an into
color as the parameter.
3:25
For this example,
we're just using a system color.
3:27
Inside the parenthesis, let's type
the class name, Color with a capital C.
3:31
And hit Enter to import it and
then add dot RED.
3:35
All right, let's give it a shot.
3:41
Now, when we first tap the button,
3:46
it should change the background
color to red and it does, cool.
3:48
Let's pause for a moment and
3:52
then we'll make some changes to
use a new color for each fact.
3:54
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