ViewBinding

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一、配置

build.gradle 文件配置

android {
    //...
    viewBinding {
        enabled = true
    }
	  //或者gradle plugin 7.0以上也可以用如下写法
		buildFeatures {
        viewBinding true
    }
}

如果希望在生成绑定类是忽略某个布局文件，tools:viewBindingIgnore="true"添加属性到布局文件的根视图中

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

<androidx.constraintlayout.widget.ConstraintLayout 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"
    **tools:viewBindingIgnore="true**">

</androidx.constraintlayout.widget.ConstraintLayout>

二、使用

2.1、创建XML视图文件

当前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生成一个绑定类。每个绑定类均包含对根视图已经具有ID 的所有视图的应用。

系统生成绑定类名称：将XML文件的名字转换为驼峰式大小写，并在末尾添加Binding一词

假设布局文件名为：fragment_customize.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>"
    android:layout_width="match_parent"

    android:layout_height="match_parent">

    <TextView
        android:id="@+id/firstView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintRight_toRightOf="parent" />

    <Button
        android:id="@+id/threeView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />


</androidx.constraintlayout.widget.ConstraintLayout>

按照上面的规则说明，系统会给我们生成FragmentCustomizeBinding 文件（文件位置在build/generated/data_binding_base_class_source_out目录下)。

// Generated by view binder compiler. Do not edit!
package xxx;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.TextView;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.constraintlayout.widget.ConstraintLayout;
import androidx.viewbinding.ViewBinding;
import androidx.viewbinding.ViewBindings;
import com.mumu.joker.R;
import java.lang.NullPointerException;
import java.lang.Override;
import java.lang.String;

public final class FragmentCustomizeBinding implements ViewBinding {
  @NonNull
  private final ConstraintLayout rootView;

  @NonNull
  public final TextView firstView;

  @NonNull
  public final Button threeView;


  private FragmentCustomizeBinding(@NonNull ConstraintLayout rootView, @NonNull TextView firstView,
      @NonNull Button threeView) {
    this.rootView = rootView;
    this.firstView = firstView;
    this.threeView = threeView;
  }

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

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

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

  @NonNull
  public static FragmentCustomizeBinding 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.firstView;
      TextView firstView = ViewBindings.findChildViewById(rootView, id);
      if (firstView == null) {
        break missingId;
      }

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

      return new FragmentCustomizeBinding((ConstraintLayout) rootView, firstView, threeView);
    }
    String missingId = rootView.getResources().getResourceName(id);
    throw new NullPointerException("Missing required view with ID: ".concat(missingId));
  }
}

所生成的绑定类具体三个属性：rootView 、firstView、threeView 。可以看到没有ID的在绑定类中是不存在引用的。

rootView 属性是私用的，可以通过getRoot()方法获取根视图的引用

2.2、在Activity中使用

在Actvity的onCreate()方法中执行以下步骤：

1. 调用绑定类的inflate()静态方法，创建绑定类的实例。
2. 调用绑定类的getRoot()方法或者kotlin的属性语法获取根视图的引用
3. 调用Activity的setContentView()方法，传递根视图对象
4. 后续即可使用绑定类的实例来引用XML任何具有ID的视图

private lateinit var binding: ActivityMainBinding


override fun onCreate(savedInstanceState: Bundle?) {
		super.onCreate(savedInstanceState)

    binding = ActivityMainBinding.inflate(layoutInflater)
    setContentView(binding.root)
  }

2.3、在Fragment中使用

在Fragment的onCreateView()方法中执行以下步骤：

1. 调用绑定类的inflate()静态方法，创建绑定类的实例。
2. 调用绑定类的getRoot()方法或者kotlin的属性语法获取根视图的引用
3. 在onCreateView()方法中返回根视图
4. 后续即可使用绑定类的实例来引用XML任何具有ID的视图

private var _binding: FragmentCustomizeBinding? = null


private val binding get() = _binding!!

override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
		_binding = FragmentCustomizeBinding.inflate(inflater, container, false)
    return binding.root
  }


override fun onDestroyView() {
    super.onDestroyView()
    _binding = null
  }