View.setTag()與View.getTag()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，以后可以用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; 
} 
} 

}