view的setTag() 和 getTag()应用 ViewHolder

转自 http://www.cnblogs.com/qingblog/archive/2012/07/03/2575140.html

View中的setTag(Onbect)表示给View添加一个格外的数据，以后可以用getTag()将这个数据取出来。 

可以用在多个Button添加一个监听器，每个Button都设置不同的setTag。这个监听器就通过getTag来分辨是哪个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;
     }
   }
 }
}

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; 
     }
   }
 }
}

在写listView 时候要重写BaseAdapter 
需要在每个item都加上button 点击button做相应操作 
这个时候需要button里面设置下 这行的属性button.setTag(item.user.name); 
然后处理button事件。 
这个东西在一些需要用到Adapter自定控件显示方式的时候非常有用 
Adapter 有个getView方法，可以使用setTag把查找的view缓存起来方便多次重用 

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();
    }
    //其他的代码可以直接使用 vh.view1、vh.view2、vh.view3 、vh.view4
}

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(); 
    }
    //其他的代码可以直接使用 vh.view1、vh.view2、vh.view3 、vh.view4
}

你可以看看android的源码，特别有listview的，你就会发现这个函数很多时候有妙用!呵呵! 
我的一点理解是，绑定数据，特别是绑定数据到view。而且可以用getTag()取得，很方便，而且是任意类型的数据，真的很酷。 
在实例BaseAdapter()的getView(position, convertView, par)里有用到。convertView这里会用到setTag() getTag()。就可以生成convertView并复用里面的widget 
一直觉得这个东西没啥用setTag()，不过只要能用上 就是比较巧的了 
在一个程序中呢 我有好多个button 我想点击一个出现1 点击第二个出现2 

for (int i = 0; i < 20; i++) {
     cells[i] = (ImageView) findViewById(cellIDs[i]);
     cells[cellnumber++].setOnClickListener(new OnClickListener() {

          public void onClick(View v){
              cellClicked(cellnumber, v);
          }
      });
}

for (int i = 0; i < 20; i++) {
     cells[i] = (ImageView) findViewById(cellIDs[i]);
     cells[cellnumber++].setOnClickListener(new OnClickListener() {
 
          public void onClick(View v){ 
              cellClicked(cellnumber, v); 
          }
      });
}

上面的代码效率不高 而且 无论点击哪一个都会出现21 当然这是我逻辑错误那怎么实现呢 

OnClickListener listener = new OnClickListener() {

     public void onClick(View v){
        int cellId = (Integer) v.getTag(); cellClicked(cellId, v);
     }
}
View v;
for (int i = 0; i < 20; i++){
    v = findViewById(cellIDs[i]);
    v.setOnClickListener(listener);
    v.setTag(i);
}

OnClickListener listener = new OnClickListener() {
 
     public void onClick(View v){ 
        int cellId = (Integer) v.getTag(); cellClicked(cellId, v); 
     }
}
View v;
for (int i = 0; i < 20; i++){ 
    v = findViewById(cellIDs[i]); 
    v.setOnClickListener(listener); 
    v.setTag(i); 
}

这样呢就实例话一个listener，同时通过tag传值就不是每一个实例都做了