Android之viewBing（视图绑定）

首先我们需要从Android studio模块编译脚本中加入依赖：

    viewBinding {
        enabled = true

    }

• 如图
  

布局文件

放置了三个button

 <Button
     android:layout_below="@+id/id_text01"
     android:text="@string/view_binding"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     android:id="@+id/id_button_1"
     ></Button>
 <Button
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     android:id="@+id/id_button_2"
     android:layout_below="@id/id_button_1"
     />

 <Button
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     android:id="@+id/id_button_3"
     android:layout_below="@id/id_button_2"
     android:text="@string/there_"
     />

加载布局

• 以前加载布局

// 老办法
setContentView(R.layout.activity_main);

• 现在加载布局

 // 新办法
 ActivityMainBinding binding = ActivityMainBinding.inflate(getLayoutInflater());
 setContentView(binding.getRoot());

• 对比

 // 老办法
 setContentView(R.layout.activity_main);
 // 新办法
 ActivityMainBinding binding = ActivityMainBinding.inflate(getLayoutInflater());
 setContentView(binding.getRoot());

获得控件

• 以前

findViewById(R.id.id_button_3).setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        Toast.makeText(MainActivity.this, "我是传统发放除法的", Toast.LENGTH_SHORT).show();
    }
});

• 现在

binding.idButton2.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        Toast.makeText(MainActivity.this,"2222", Toast.LENGTH_SHORT).show();
    }
});

• 对比

binding.idButton2.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        Toast.makeText(MainActivity.this,"2222", Toast.LENGTH_SHORT).show();
    }
});

findViewById(R.id.id_button_3).setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        Toast.makeText(MainActivity.this, "我是传统发放除法的", Toast.LENGTH_SHORT).show();
    }
});

需要说明的

首先可以注意到在xml的布局文件里面，控件id的名命都是依靠下划线来进行分割的。

但是在java代码中调用的时候，却丢失了下划线转化成了驼峰命名。

这是因为Android view的优化机制导致的。
如果想要细看的话可以打开自己编译生成的文件。会多出来一个文件就是viewbinding自动生成的文件。

// Generated by view binder compiler. Do not edit!
package com.example.learnandroidfromgoogle.databinding;

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

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

  @NonNull
  public final Button idButton1;

  @NonNull
  public final Button idButton2;

  @NonNull
  public final RelativeLayout idRelative;

  @NonNull
  public final TextView idText01;

  private ActivityMainBinding(@NonNull ConstraintLayout rootView, @NonNull Button idButton1,
      @NonNull Button idButton2, @NonNull RelativeLayout idRelative, @NonNull TextView idText01) {
    this.rootView = rootView;
    this.idButton1 = idButton1;
    this.idButton2 = idButton2;
    this.idRelative = idRelative;
    this.idText01 = idText01;
  }

  @Override
  @NonNull
  public ConstraintLayout 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.
    String missingId;
    missingId: {
      Button idButton1 = rootView.findViewById(R.id.id_button_1);
      if (idButton1 == null) {
        missingId = "idButton1";
        break missingId;
      }
      Button idButton2 = rootView.findViewById(R.id.id_button_2);
      if (idButton2 == null) {
        missingId = "idButton2";
        break missingId;
      }
      RelativeLayout idRelative = rootView.findViewById(R.id.id_relative);
      if (idRelative == null) {
        missingId = "idRelative";
        break missingId;
      }
      TextView idText01 = rootView.findViewById(R.id.id_text01);
      if (idText01 == null) {
        missingId = "idText01";
        break missingId;
      }
      return new ActivityMainBinding((ConstraintLayout) rootView, idButton1, idButton2, idRelative,
          idText01);
    }
    throw new NullPointerException("Missing required view with ID: ".concat(missingId));
  }
}

本文参考了以下内容：

• Android官网教程