如何从包含合并标签的布局访问视图，该标签包含在另一个布局中？

Question

我使用 Android Studio 3.6-RC1 和构建工具版本 3.6.0-rc01 并遇到了 ViewBinding 功能的问题：

我有带有以下标记的 activity_test.xml 文件：

<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>

以及带有以下标记的merge_view.xml：

<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>

活动代码如下所示：

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"

    }
}

问题是当我尝试从合并布局访问 TextView 时，应用程序会抛出异常并显示消息 java.lang.NullPointerException: Missing required view with ID: viewMerged.

生成的绑定类如下所示：

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));
  }
}

我是否遗漏了什么，或者无法从包含的带有标签的布局中访问视图，或者它尚未在 Android Studio 3.6-RC1 中提供？

Answer 1

我写了一篇关于使用带有<merge>标签的ViewBinding的文章，你可以找到here

基本上，你需要做的是

• 不要给<include>标签任何ID。
• 调用生成的合并布局绑定的bind() 方法，传递包含布局的布局的根视图。
• 从合并绑定对象访问您的视图

例如，您有merge_view.xml，因此您将生成MergeViewBinding 类，这就是您从该布局访问视图的方式。

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

只需使用视图/文件的绑定。这是一个例子：

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)

    ...
}

查看示例：

<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>

确保，您首先构建它，以便生成 Binding。