android data binding with a custom view

Question

The Android data binding guide discusses binding values within an activity or fragment, but is there a way to perform data binding with a custom view?

I would like to do something like:

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <com.mypath.MyCustomView
        android:id="@+id/my_view"
        android:layout_width="match_parent"
        android:layout_height="40dp"/>

</LinearLayout>

with my_custom_view.xml:

<layout>

<data>
    <variable
        name="myViewModel"
        type="com.mypath.MyViewModelObject" />
</data>

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@{myViewModel.myText}" />

</LinearLayout>

</layout>

While it appears possible to do this by setting custom attributes on the custom view, this would quickly become cumbersome if there's a lot of values to bind.

Is there a good way to accomplish what I'm trying to do?

Answer 1

In your Custom View, inflate layout however you normally would and provide a setter for the attribute you want to set:

private MyCustomViewBinding mBinding;
public MyCustomView(...) {
    ...
    LayoutInflater inflater = (LayoutInflater)
        context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    mBinding = MyCustomViewBinding.inflate(inflater);
}

public void setMyViewModel(MyViewModelObject obj) {
    mBinding.setMyViewModel(obj);
}

Then in the layout you use it in:

<layout xmlns...>
    <data>
        <variable
            name="myViewModel"
            type="com.mypath.MyViewModelObject" />
    </data>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <com.mypath.MyCustomView
            android:id="@+id/my_view"
            app:myViewModel="@{myViewModel}"
            android:layout_width="match_parent"
            android:layout_height="40dp"/>

    </LinearLayout>
</layout>

In the above, an automatic binding attribute is created for app:myViewModel because there is a setter with the name setMyViewModel.

Answer 2

First, don't do this if this custom view is already being <include> in another layout, such as activity etc. You'll just get an exception about the tag being unexpected value. The data binding already ran the binding on it, so you're set.

Did you try using onFinishInflate to run the bind? (Kotlin example)

override fun onFinishInflate() {
    super.onFinishInflate()
    this.dataBinding = MyCustomBinding.bind(this)
}

Keep in mind that if you use the binding in your view, it won't be able to be created programmatically, at least it would be very convoluted to support both even if you can.

Answer 3

Following the solution presented by george the graphical editor in android studio was no longer able to render the custom view. The reason is, that no view is actually inflated in the following code:

public MyCustomView(...) {
    ...
    LayoutInflater inflater = (LayoutInflater)
        context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    mBinding = MyCustomViewBinding.inflate(inflater);
}

I suppose that the binding handles the inflation, however the graphical editor did not like it.

In my specific use case I wanted to bind a single field and not an entire view model. I came up with (kotlin incoming):

class LikeButton @JvmOverloads constructor(
        context: Context,
        attrs: AttributeSet? = null,
        defStyleAttr: Int = 0
) : ConstraintLayout(context, attrs, defStyleAttr) {

    val layout: ConstraintLayout = LayoutInflater.from(context).inflate(R.layout.like_button, this, true) as ConstraintLayout

    var numberOfLikes: Int = 0
      set(value) {
          field = value
          layout.number_of_likes_tv.text = numberOfLikes.toString()
      }
}

The like button consists of an image and a text view. The text view holds the number of likes, which I want to set via data binding.

By using the setter for numberOfLikes as an attribute in the following xml, data binding automatically makes the association:

<views.LikeButton
  android:id="@+id/like_btn"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  app:numberOfLikes="@{story.numberOfLikes}" />

Further reading: https://medium.com/google-developers/android-data-binding-custom-setters-55a25a7aea47

Answer 4

There are some good answers on here already, but I wanted to offer what I believe to be the simplest.

Create your custom control with the layout tags surrounding it, just like any other layout. See the following toolbar for example. this gets used in each of the activity classes

<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto">

<data>
    <variable name="YACustomPrefs" type="com.appstudio35.yourappstudio.models.YACustomPreference" />
</data>

<android.support.design.widget.CoordinatorLayout
    android:layout_width="match_parent"
    android:layout_height="?attr/actionBarSize">

    <android.support.design.widget.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/YATheme.AppBarOverlay">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="@color/colorPrimary"
            app:popupTheme="@style/YATheme.PopupOverlay"/>

    </android.support.design.widget.AppBarLayout>

</android.support.design.widget.CoordinatorLayout>

Now this custom layout is a child of every Activity. You simply treat it as such in the onCreate binding setup.

  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    binding = DataBindingUtil.setContentView(this, R.layout.activity_main)
    binding.yaCustomPrefs = YACustomPreference.getInstance(this)
    binding.toolbarMain?.yaCustomPrefs = YACustomPreference.getInstance(this)
    binding.navHeader?.yaCustomPrefs = YACustomPreference.getInstance(this)

    binding.activity = this
    binding.iBindingRecyclerView = this
    binding.navHeader?.activity = this

    //local pointer for notify txt badge
    txtNotificationCountBadge = txtNotificationCount

    //setup notify if returned from background so we can refresh the drawer items
    AppLifeCycleTracker.getInstance().addAppToForegroundListener(this)

    setupFilterableCategories()
    setupNavigationDrawer()
}

Notice I set the children's content at the same time I do the parent and it is all done through dot notation access. As long as the files are surrounded with layout tags and you named them, it is simple to do.

Now if the custom class has it's own associated code inflation, then it can easily just do it's own binding in it's onCreate or constructor, but you get the picture. If you have your own class just throw the following in the constructor to match it's named binding class. It follows the name convention of the layout file pascal cased, so it's easy to find and auto fill.

    LayoutInflater inflater = (LayoutInflater)
    context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
mBinding = NameOfCustomControlBinding.inflate(inflater);

Hope that helps.