Jetpack——viewbinding

viewbinding是什么？

视图绑定是一项可让您更轻松地编写与视图交互的代码的功能。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。

viewbinding解决什么问题？

用于代替findViewById()

viewbinding实现

在build.gradle中添加

android {
    ...
    buildFeatures {
        viewBinding = true
    }
}

对于每一个布局都会生成一个Binding类，如activity_main.xml会生成ActivityMainBinding

<?xml version="1.0" encoding="utf-8"?>

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

    <TextView
        android:id="@+id/tv"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

</LinearLayout>

对于每个带id的控件都会生成对应变量

class MainActivity : AppCompatActivity() {

    private lateinit var binding: ActivityMainBinding

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)
        binding.tv.text = "AAA"
    }
}

viewbanding源码解析

在build目录下会生成Binding类，如下

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

  @NonNull
  public final LinearLayout main;

  @NonNull
  public final TextView tv;

  private ActivityMainBinding(@NonNull LinearLayout rootView, @NonNull LinearLayout main,
      @NonNull TextView tv) {
    this.rootView = rootView;
    this.main = main;
    this.tv = tv;
  }

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

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

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

  @NonNull
  public static ActivityMainBinding 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: {
      LinearLayout main = (LinearLayout) rootView;

      id = R.id.tv;
      TextView tv = ViewBindings.findChildViewById(rootView, id);
      if (tv == null) {
        break missingId;
      }

      return new ActivityMainBinding((LinearLayout) rootView, main, tv);
    }
    String missingId = rootView.getResources().getResourceName(id);
    throw new NullPointerException("Missing required view with ID: ".concat(missingId));
  }
}

ViewBindings类如下

public class ViewBindings {

    private ViewBindings() {
    }

    /**
     * Like `findViewById` but skips the view itself.
     *
     * @hide
     */
    @Nullable
    public static <T extends View> T findChildViewById(View rootView, @IdRes int id) {
        if (!(rootView instanceof ViewGroup)) {
            return null;
        }
        final ViewGroup rootViewGroup = (ViewGroup) rootView;
        final int childCount = rootViewGroup.getChildCount();
        for (int i = 0; i < childCount; i++) {
            final T view = rootViewGroup.getChildAt(i).findViewById(id);
            if (view != null) {
                return view;
            }
        }
        return null;
    }
}

原文地址：https://blog.csdn.net/qq_35258036/article/details/145195117

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