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Now that we've covered a bit of the generated code, it's time to write our own! In this video we'll write Kotlin code in our FunFactsActivity class to declare our TextView and Button.
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[MUSIC]
0:00
Now that we're comfortable using
the design editor to make changes to our
0:04
layouts, it's time to write some code.
0:08
Let's start by taking a look
at some of the code that was
0:10
automatically generated for our project.
0:13
Using the Android perspective
makes our code easy to find,
0:16
it's right here in the java folder.
0:20
But if you happened to be
in the project perspective.
0:22
Remember that our Java code can be found
at app > source > main > and then Java.
0:26
It's right above our resources folder.
0:32
Let's switch back to
the Android perspective and
0:35
take a look inside the java folder.
0:38
Now we can see the package name we
chose when we created our project.
0:41
This is where all of our
code will go by default.
0:45
Inside this package,
we'll find one file, FunFactsActivity.
0:48
And if we double click it,
it opens up over here in the code editor.
0:53
Now we can close the rest of these files.
0:58
Let's right click on FunFactsActivity
up here and choose Close Others.
1:00
And I'll also close the project pane.
1:07
In Android, an activity represents
a screen that users can interact with.
1:10
We'll learn much more about
activities later but for
1:15
now, let's focus on this onCreate method.
1:17
The onCreate method is called when
our activity is first created.
1:21
And since our app only has one activity,
1:24
this onCreate method will be called
when our app is first started.
1:27
You might have noticed that this
method also has one parameter,
1:31
a bundled variable called
savedInstanceState.
1:34
We won't be using this variable in
our app, so let's ignore it for now.
1:38
Inside onCreate, the most important
line is the call to setContentView.
1:42
This method tells the activity which
layout file we want to use for the screen.
1:47
This R.layout.activity_fun_facts
parameter, is an ID
1:51
which points to the activity_fun_facts
XML file and the layout directory.
1:56
This is where the layout we've been
working on gets attached to our activity.
2:01
Okay, time to make the magic happen.
2:06
The first thing we need to do is declare
two properties or member variables.
2:08
One for our FunFact text view and
one for our button.
2:13
A property is the name for
a variable that is inside the class but
2:16
outside all of the methods.
2:21
Using properties for
2:23
our views means that we'll be able to
access them from any method in our class.
2:24
This is especially useful because there's
often more than one method that needs
2:29
access to our views.
2:33
Let's start by adding a line
at the top of the class.
2:34
Then let's add a comment to
help explain what we're doing.
2:39
Remember it's two forward slashes for
a single line comment.
2:42
Let's type slash, slash space and
then type Declare our View variables.
2:46
Then on a new line let's declare our
fun fact text view as private var
2:54
factTextView, Then since,
3:00
we're using colon,
we also need to set it equal to something.
3:05
But we won't have access to our text
view and until the onCreate method.
3:10
So for now, let's just set it equal to no.
3:15
Let's have a colon and then for
the data type, let's use TextView but
3:18
add a question mark to the end to
let colon know it might be null.
3:23
Then let's set it equal to null and
there we go.
3:29
Also, if TextView is in red, that just
means it hasn't been imported yet.
3:33
Hit Alt+Enter to import it.
3:38
One more thing, note that we won't be
using the m prefix for our properties.
3:40
Sometimes, when you see Android code, they
might declare their variables like this.
3:45
And according to the Android
source style guide, all fields or
3:51
properties should start
with a lower case m.
3:54
However, most code isn't written that way.
3:58
So unless you plan on contributing
to Android source code,
4:01
feel free to drop the m prefix
as we'll be doing here.
4:04
If you'd like to read more
about these style guidelines,
4:08
check out the link in
the teacher's notes below.
4:11
Now we need to declare our button.
4:13
Let's add a new line in our TextView and
type private var showFactButton.
4:15
Then, let's add a colon and for
the type, start typing Button.
4:22
Notice that Android Studio is
trying to guess what we're typing.
4:28
Once the top choice is button,
hit Enter or
4:32
Tab to let Android Studio
autocomplete that for us.
4:35
It even adds the import statement.
4:39
Then, to finish it up,
let's add a question mark and equals null.
4:41
All right, but why do these
names change to gray like this?
4:47
If we hover over one of our properties,
4:52
we get a quick tip saying that
our Property is never used.
4:54
The gray coloring will go away
once we use these variables.
4:57
Another thing I want to point
out are the import statements,
5:01
we can view them by hitting
the little plus button up here.
5:04
By default,
our class only has a couple of imports,
5:08
but every time we use a new
class like TextView or button.
5:11
Android Studio will try to automatically
add the corresponding import statement,
5:15
if you use a class that
isn't important yet.
5:20
Let say I delete the button import.
5:23
Then you'll have something
it'll look like this.
5:27
To fix it, just place your
cursor in the missing class and
5:30
hit Alt+Enter to import it.
5:34
Let's take a short break and
5:36
then we'll see how to assign our
views to these new variables.
5:38
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