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Awesome now it's time to assign
values to these new variables.

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00:00:04,840 --> 00:00:08,260
Let's start by adding four new
lines to the bottom of onCreate.

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Then on the second new line
let's add a comment, // Assign

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the Views from the layout file
to the corresponding variables.

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00:00:26,030 --> 00:00:28,780
It's important that we don't
assign the views until

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after the call to setContentView.

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If we try to access a view from our
layout before calling setContentView,

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it won't exist and we'll get an error.

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On the next line, let's start typing
factTextView and then an = sign.

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And now what we need is a method that will
take in the ID that we set on the layout

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and return our TextView.

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Fortunately, every activity has a method
for this, and it's called findViewById.

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Let's start typing findViewById
after the equals sign.

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00:01:02,304 --> 00:01:07,054
And notice that as you're typing the auto
complete feature is filling it in below.

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Android Studio analyzes what we're
typing offers suggestions that

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match what we've typed so far.

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Automatic code completion is awesome,
it's super convenient, and it makes it so

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that we only need to remember
the first few letters of something and

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Android Studio will take care of the rest.

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Now we can either finish
typing this method, or

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we can just hit Enter to select
it from code completion.

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And now we see a hint about
the parameter we need to use here.

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The findViewById method requires
an ID as its parameter.

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But rather than just type
in the ID from the layout,

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we must refer to it through
a generated resource class.

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When we built our project,
Android automatically builds a class for

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us called simply R,
which stands for resources.

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This class contains all
the IDs of our files and

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the res directory, as well as a ton
of other default resource IDs.

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If we open the project pane and

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switch to the project perspective and
then drill into app,

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build, generated, source, r, debug, and

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then our package name,
we can even open the R class.

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Though notice at the top
there's a warning saying,

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files under the build folder
are generated and should not be edited.

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We're not here to edit anything, it's just
nice to know where the R class comes from.

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Let's close this and
switch back to the Android perspective.

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And I'll hide the project pane again.

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Back in funfactsactivity.java,
let's type a capital R followed by a dot.

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Then we need to pick which type
of resource we're looking for.

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Since we're looking for an ID,
let's type id followed by another dot.

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And look at that, it's showing us
the IDs that we set in our layout.

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Let's pick factTextView, and
hit Enter to select it, and semicolon.

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00:03:07,441 --> 00:03:11,582
Now depending on which version
of Android you're using,

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you might see an error, like I do, or

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if you're targeting a newer version of
Android, everything will be just fine.

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So what happened?

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Let's take a look at some code to see what
changed in the new version of Android.

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Here we've got a Java project where
we've mocked out some classes from

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the Android API.

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We start by creating a fake view class,
and

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then we create a button and text view
classes that extend from our view class.

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Then we create an activity class and give
it a findViewById method that takes in

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an integer and returns a view, just like
you'd find in the actual activity class.

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Inside this method,
we create a local view variable.

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And depending on whether the ID is
a one or a two, we set it equal to

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either a new button or a new text view
before returning a view variable.

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Finally we've got a main activity class
which extends from activity, and inside

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that class' constructor we try to set up
two variables, a button and a text view.

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This is the same error I'm getting back
in Android Studio, incompatible types.

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It's expecting a button but we're
setting it equal to a view to fix this.

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Since we know that findViewById
with the parameter

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of 1 will indeed return a button,
we can just cache the returned

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value to a button by adding
the word Button and parentheses.

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And we can do the same thing for

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a text view by using Alt Enter
to apply a quick fix.

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However, in Android Oreo they
made a change to the way we

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use findViewById that means
we no longer need the cast.

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So let's undo the casts.

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And now let's take a look at how they
change the findViewById function.

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Up in the findViewById method,
instead of returning a view,

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we want to use something called generics
to let us return multiple types.

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Don't worry too much if this
part doesn't make sense.

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What's important is how it affects our
view variables, not how it's implemented.

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Let's start by declaring our generic and

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what types it's allowed to
have inside angle brackets.

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Here we're declaring a generic,
named T, and

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saying it can only be a class
with the view class as a parent.

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Then instead of returning a view,
let's return our new generic type, T.

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Finally since we've changed the return
type from View to our generic type

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that extends View, we need to add a cast
to our view variable before we return it.

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00:06:00,746 --> 00:06:07,275
Perfect, now we no longer need to add
a cast to our findViewById calls.

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00:06:07,275 --> 00:06:10,510
Though since this change is fairly recent,
you're likely to encounter

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a lot of code that still uses
casts with findViewById.

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00:06:15,530 --> 00:06:18,530
So if you see any code
that's still using casts and

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it's not giving you issues,
feel free to ignore it.

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00:06:21,820 --> 00:06:24,320
You're just on a newer version
of Android than we are.