如何从包含合并标记的布局访问视图包含在另一个布局中？

Question

I use Android Studio 3.6-RC1 and build tools version 3.6.0-rc01 and encountered an issue with ViewBinding feature:

I have activity_test.xml file with the following markup:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <include
        android:id="@+id/view_merged"
        layout="@layout/merge_view" />
</LinearLayout>

And merge_view.xml with following markup:

<merge xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:id="@+id/label"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Merge view" />
</merge>

Activity code looks like the following:

class TestActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        val binding = ActivityTestBinding.inflate(layoutInflater)
        setContentView(binding.root)

        binding.viewMerged.label.text = "New text"

    }
}

Problem is when I try to access TextView from merged layout, the app throws an exception with the message java.lang.NullPointerException: Missing required view with ID: viewMerged.

The generated binding class looks like the following:

public final class ActivityTestBinding implements ViewBinding {
  @NonNull
  private final LinearLayout rootView;

  @NonNull
  public final MergeViewBinding viewMerged;

  private ActivityTestBinding(@NonNull LinearLayout rootView,
      @NonNull MergeViewBinding viewMerged) {
    this.rootView = rootView;
    this.viewMerged = viewMerged;
  }

  @Override
  @NonNull
  public LinearLayout getRoot() {
    return rootView;
  }

  @NonNull
  public static ActivityTestBinding inflate(@NonNull LayoutInflater inflater) {
    return inflate(inflater, null, false);
  }

  @NonNull
  public static ActivityTestBinding inflate(@NonNull LayoutInflater inflater,
      @Nullable ViewGroup parent, boolean attachToParent) {
    View root = inflater.inflate(R.layout.activity_test, parent, false);
    if (attachToParent) {
      parent.addView(root);
    }
    return bind(root);
  }

  @NonNull
  public static ActivityTestBinding bind(@NonNull View rootView) {
    // The body of this method is generated in a way you would not otherwise write.
    // This is done to optimize the compiled bytecode for size and performance.
    String missingId;
    missingId: {
      View viewMerged = rootView.findViewById(R.id.view_merged);
      if (viewMerged == null) {
        missingId = "viewMerged";
        break missingId;
      }
      MergeViewBinding viewMergedBinding = MergeViewBinding.bind(viewMerged);
      return new ActivityTestBinding((LinearLayout) rootView, viewMergedBinding);
    }
    throw new NullPointerException("Missing required view with ID: ".concat(missingId));
  }
}

Am I missing something or there is no way to access views from included layouts with tags or it is not yet shipped in Android Studio 3.6-RC1?

Answer 1

I wrote an article about using ViewBinding with <merge> tag which you can find here

Basically, what you need to do is

• Don't give <include> tag any ID.
• Call bind() method of generated merge layout binding, passing the root view of the layout you included your layout in.
• Access your view from the object of merge binding

For example, you have merge_view.xml so you'll have MergeViewBinding class generated and this is how you will access the view from this layout.

class TestActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        val binding = ActivityTestBinding.inflate(layoutInflater)
        val mergeBinding = MergeViewBinding.bind(binding.root)
        setContentView(binding.root)
        mergeBinding.label.text = "New text"
    }
}

Answer 2

Simply use the binding of the view/file. Here is an example:

import ch.zkb.mobile.bank.databinding.MyFragmentBinding
import ch.zkb.mobile.bank.databinding.MyMergeBinding

class MyFragment : (R.layout.my_fragment) {

    private val binding by viewBinding(MyFragmentBinding::bind)
    private val mergeBinding by viewBinding(MyMergeBinding::bind)

    ...
}

View example:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <include layout="@layout/my_merge" />

</LinearLayout>

Make sure, you build it first, so the Binding is generated.