android - 如何从包含合并标签的布局访问 View ，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>

并带有以下标记的 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>

Activity 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(bind)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 View ，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 ViewBinding 和 <merge> 的文章您可以找到的标签 here

基本上，你需要做的是

不给<include>标记任何 ID。

调用 bind()生成合并布局绑定(bind)的方法，传递包含布局的布局的 Root View 。

从合并绑定(bind)的对象访问您的 View

例如，您有 merge_view.xml所以你会有 MergeViewBinding生成的类，这就是您从该布局访问 View 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"
    }
}