[MUSIC]

[SOUND] Welcome back.

When we last visited Stormy, it was looking great with its amazing interface.

But behind the scenes, I think it was still feeling a bit under the weather.

Because it still can't use the data we worked so

hard to get from the Dark Sky API.

Thinking back to our MVC design, where should we wire all of this together?

That's right, the controller, which for this project is our main activity.

Let's use Android's data binding library to help us connect our data to our view,

and do so in an efficient manner.

This library allows us to reduce the boilerplate code we have seen in other

projects with member variable, decorations, and using find view by ID.

We can bind our layout, and logic together in a flexible manner.

There's one thing I definitely like to mention here before we see this in

action though.

While using the data binding library is efficient,

it is just one approach to connect data from a model to a view.

Please don't think of this as the way to do these tasks, but

simply a way to do them.

With that in mind, let's get started.

As I mentioned, with the Android data binding library, we don't need to go

through the member variable creation, and find view by ID process.

Let's have a look at the documentation to see what it says about how to get set up.

Looks like we need to enable data binding in our build environment.

And then we need to make some changes to our layout file a little bit.

And then we can bind our data to our view.

Should be relatively straightforward.

Let's head into Android Studio, and make these changes.

First, we need to head into our apps build.gradle་file, and

enable data binding.

So here in the Android section,

we need to add dataBinding,

enabled = true.

Since we made a change to the gradle file, we need to re-sync.

The next step is to go into the XML file for the activity, and make a few changes.

We'll go here into our text.

Go back up to the top.

We'll need to add a new level to our XML hierarchy called layout.

And we'll add a new data element.

Android uses this layout to generate a binding class

where all the bindings from the layout properties are held.

Let's get our XML set up, and then we'll talk about what's going on.

So we'll need to add a new tag, Of layout.

Up here at the top.

We'll cut and paste the closing one.

And put it down at the bottom.

And then we need to cut and

paste our XML namespace information into the opening layout tag.

So we go back up here to the top.

We want cut that.

And paste it in there.

Great, now we're back to a valid XML document.

One other area needs to be added here to allow us access to our data.

It's actually called a data element, and that's easy to remember.

So we'll add a data element.

Inside our data tags, we want to define a variable.

Which, according to the documentation,

describes a property that may be used within this layout.

So we'll do variable.

Since we're working with weather, let's name it weather.

And we want to assign it a type of our current weather, and

we use the package name to get to that.

So type com.teamtreehouse.stormy.CurrentWeather.

Terrific.

So what's going on here?

Well, the Android data binding library is going to generate a binding class for

us based on this information.

The name of the generated class is based on the name of the layout file.

The name is then converted to Pascal case.

Meaning the first letter of all the words are uppercased, and

adding the word binding as a suffix.

In our case here, our layout is called activity_main.xml.

So the class generated by data binding is called ActivityMainBinding.

We can use this over a main activity to connect our data to our view.

Before we do that, let's use our newly bound data to set one value in the layout.

Let's look for our summary text view.

timeValue, locationValue.

SummaryValue.

Here it is with our default value of Stormy with a chance of meatballs.

We want to update that to use our data.

To access our data, we use the @ symbol, followed by a pair of curly braces.

Inside the curly braces,

we use the variable name we assigned in the data element up at the top.

Then a period, and then the data point we want to use.

So in this case, here for Android text, we would type @,

the curly braces, our variable name was weather,

and our element is summary.

Okay, I don't want to leave you in a bind but

before we change all of these values, we need to update our data model slightly.

And then we need to go into main activity to set all this up programmatically.

We'll do that next.