ViewBinding技术

1. ViewBinding视图绑定

$~~~~$在模块中启用视图绑定之后，系统会为该模块中的每个 XML 布局文件生成一个绑定类。绑定类的实例包含对在相应布局中具有 ID 的所有视图的直接引用。通过视图绑定功能，可以替代findViewById，从而更轻松地编写可与视图交互的代码。

2. 使用条件

$~~~~$视图绑定在 Android Studio 3.6 Canary 11 及更高版本中可用。

3. 开启视图绑定

android {
 viewBinding {
    enabled = true
  }
}

4. 忽略某个布局文件的视图绑定

<LinearLayout
    tools:viewBindingIgnore="true" >
</LinearLayout>

5. 生成XML绑定类

$~~~~$为某个模块启用视图绑定功能后，系统会为该模块中包含的每个XML布局文件各生成一个绑定类。每个绑定类均包含对根视图以及具有ID的所有视图的引用。绑定类的名称为：XML文件的名称转换为驼峰式大小写+Binding。

XML文件： activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">
    <TextView
        android:id="@+id/tv_hello_world"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

$~~~~$自动生成绑定类文件：

ActivityBleBinding.java
public final class ActivityBleBinding implements ViewBinding {
  @NonNull
  private final RelativeLayout rootView;
  @NonNull
  public final FloatingActionButton floatingButton;
  @NonNull
  public final LinearLayout llAdapterTip;
  @NonNull
  public final RecyclerView recyclerView;
  @NonNull
  public final SwipeRefreshLayout swipeLayout;
  @NonNull
  public final TextView tvAdapterStates;
  @NonNull
  public final TextView tvTip;
  private ActivityBleBinding(@NonNull RelativeLayout rootView,
      @NonNull FloatingActionButton floatingButton, @NonNull LinearLayout llAdapterTip,
      @NonNull RecyclerView recyclerView, @NonNull SwipeRefreshLayout swipeLayout,
      @NonNull TextView tvAdapterStates, @NonNull TextView tvTip) {
    this.rootView = rootView;
    this.floatingButton = floatingButton;
    this.llAdapterTip = llAdapterTip;
    this.recyclerView = recyclerView;
    this.swipeLayout = swipeLayout;
    this.tvAdapterStates = tvAdapterStates;
    this.tvTip = tvTip;
  }
  @Override
  @NonNull
  public RelativeLayout getRoot() {
    return rootView;
  }
  @NonNull
  public static ActivityBleBinding inflate(@NonNull LayoutInflater inflater) {
    return inflate(inflater, null, false);
  }
  @NonNull
  public static ActivityBleBinding inflate(@NonNull LayoutInflater inflater,
      @Nullable ViewGroup parent, boolean attachToParent) {
    View root = inflater.inflate(R.layout.activity_ble, parent, false);
    if (attachToParent) {
      parent.addView(root);
    }
    return bind(root);
  }
  @NonNull
  public static ActivityBleBinding 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.
    int id;
    missingId: {
      id = R.id.floatingButton;
      FloatingActionButton floatingButton = rootView.findViewById(id);
      if (floatingButton == null) {
        break missingId;
      }
      id = R.id.ll_adapter_tip;
      LinearLayout llAdapterTip = rootView.findViewById(id);
      if (llAdapterTip == null) {
        break missingId;
      }
      id = R.id.recyclerView;
      RecyclerView recyclerView = rootView.findViewById(id);
      if (recyclerView == null) {
        break missingId;
      }
      id = R.id.swipeLayout;
      SwipeRefreshLayout swipeLayout = rootView.findViewById(id);
      if (swipeLayout == null) {
        break missingId;
      }
      id = R.id.tv_adapter_states;
      TextView tvAdapterStates = rootView.findViewById(id);
      if (tvAdapterStates == null) {
        break missingId;
      }
      id = R.id.tv_tip;
      TextView tvTip = rootView.findViewById(id);
      if (tvTip == null) {
        break missingId;
      }
      return new ActivityBleBinding((RelativeLayout) rootView, floatingButton, llAdapterTip,
          recyclerView, swipeLayout, tvAdapterStates, tvTip);
    }
    String missingId = rootView.getResources().getResourceName(id);
    throw new NullPointerException("Missing required view with ID: ".concat(missingId));
  }
}

$~~~~$该类实现了ViewBinding接口，： ViewBinding.java

/** A type which binds the views in a layout XML to fields. */
public interface ViewBinding {
    /**
     * Returns the outermost {@link View} in the associated layout file. If this binding is for a
     * {@code <merge>} layout, this will return the first view inside of the merge tag.
     */
    @NonNull
    View getRoot();
}

6. 使用绑定类文件