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Adapter Class & ViewHolder Sub-Class
5:45Let's create an Adapter!
With our good start and what will be our
user interface, we now need to create
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our adapter class and ViewHolder subclass
to connect our data to our display.
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Since the adapter relies on the
ViewHolder, we'll tackle that code first.
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The ViewHolder is a subclass
that resides inside our adapter.
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Let's get that adapter class all set up.
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To keep a clean code base,
let's make a new package called adapters.
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New package, Adapters.
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And inside here, do a new Java class.
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We'll name it HourlyAdapter.
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And the superclass, it's gonna
come from the RecycleView.Adapter.
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And hit OK.
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And first thing, we get an error.
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We hover over the error,
it shows about how this class
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must either be declared abstract or
implement the abstract method listed.
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If we do the quick fix,
there's an option to implement methods.
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Implement methods, we want all of those,
so we'll select them all and hit OK.
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And with the magic of Android Studio,
our methods are set up and
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our errors are gone.
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We see that Android Studio has added
some annotations in here for us as well.
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We're overriding some and
we have this NonNull annotation too.
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If that one is unfamiliar to you, it
allows the compiler to determine cases where
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a code path might receive a null value.
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And it helps to prevent
NullPointerExceptions.
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Check the teacher's notes for
more information on NonNull annotations.
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We need to write our subclass for
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our ViewHolder which will describe
the views within each row item.
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Let's come down here to the bottom.
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We'll give some space.
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We'll do public class ViewHolder and
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we want it to extend from
RecyclerView.ViewHolder.
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And we see, there's another error.
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This error says there is no
default constructors available.
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Now, we'll fix that here in a second.
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But with our ViewHolder subclass defined,
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we can specify it up in our
adapter class definition.
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We're gonna use HourlyAdapter.ViewHolder.
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All right.
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Let's head back to our sub class
where there's a few things to add.
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We want our binding variables,
and we want our constructor.
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Our constructor will do view lookups for
each subview.
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Okay.
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Let's start with the binding.
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Recall that by using the Android data
binding library, it generates a class for
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us based on the layout name.
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By default, the name of the class is
based on the name of the layout file,
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converts it to pascal case, and
adds the binding suffix to it.
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In this case, it is HourlyListItemBinding.
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So we'll do public HourlyListItemBinding,
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and it cannot resolve that symbol.
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Let's see.
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We have a typo here in our name for
list_item.xml.
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Let's refactor and rename that.
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Clean that up.
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Okay.
So sometimes,
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Android Studio doesn't do our import
of our binding for us automatically.
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We'll do a quick fix to do our import.
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And now, for our constructor.
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So we want public ViewHolder.
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It will take an HourlyListItemBinding
as our parameter.
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HourlyLayoutBinding is
what we'll call that.
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So inside the constructor,
we call super in passing our binding.
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So super(hourlyLayoutBinding).
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And then, we also need a call to getRoot,
which returns the outermost view in
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the layout file associated
with our particular binding.
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And then we connect our bindings.
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hourlyListItemBinding =
hourlyLayoutBinding.
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That was kinda of a lot.
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Let's go over that one more time.
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Our ViewHolder extends from
RecyclerView.ViewHolder, and
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we bind the variables that
are being used inside the view.
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Then, we create a constructor for
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this ViewHolder class to do
view lookups for each subview.
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The constructor takes an item binding as
the parameter, which we pass into super
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inside the constructor and
call getRoot to grab the outermost view.
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Then, we connect the bindings together.
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And that's it for the ViewHolder.
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Let's take a quick break to get up and
stretch a bit,
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and then get the rest
of the adapter set up.
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