View.setTag()的作用

這個東西在一些需要用到Adapter自定控件顯示方式的時候非常有用
Adapter 有個getView方法，可以使用setTag把查找的view緩存起來方便多次重用
public View getView(int position, View convertView, ViewGroup parent) {
       ViewHolder vh;

       if (convertView == null) {
               LayoutInflater inflater = (LayoutInflater) mWidgetsSwitchApp
                               .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
               convertView = inflater.inflate(R.layout.app_gallery_item, null);
               vh = new ViewHolder();
               vh.view1 = (ImageView) convertView.findViewById(R.id.view1);
               vh.view2 = (ImageView) convertView.findViewById(R.id.view2);
               vh.view3= (ImageView) convertView.findViewById(R.id.view3);
               vh.view4 = (ImageView) convertView.findViewById(R.id.view4);
               convertView.setTag(vh);
       } else {
               vh = (ViewHolder) convertView.getTag();
       }
//其他的代碼可以直接使用 vh.view1、vh.view2、vh.view3 、vh.view4
}

View中的setTag（Onbect）表示給View添加一個格外的數據，以後可以用getTag()將這個數據取出來。

可以用在多個Button添加一個監聽器，每個Button都設置不同的setTag。這個監聽器就通過getTag來分辨是哪個Button 被按下。

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class Main extends Activity {

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Button button1 = (Button) findViewById(R.id.Button01);
Button button2 = (Button) findViewById(R.id.Button02);
Button button3 = (Button) findViewById(R.id.Button03);
Button button4 = (Button) findViewById(R.id.Button04);
MyListener listener = new MyListener();
button1.setTag(1);
button1.setOnClickListener(listener);
button2.setTag(2);
button2.setOnClickListener(listener);
button3.setTag(3);
button3.setOnClickListener(listener);
button4.setTag(4);
button4.setOnClickListener(listener);
}

public class MyListener implements View.OnClickListener {

@Override
public void onClick(View v) {
int tag = (Integer) v.getTag();
switch (tag) {
case 1:
System.out.println(“button1 click”);
break;
case 2:
System.out.println(“button2 click”);
break;
case 3:
System.out.println(“button3 click”);
break;
case 4:
System.out.println(“button4 click”);
break;
}
}

}

}