Android中View的setTag与getTag行为理解一例

public class ViewHolderAdapter extends ArrayAdapter {
    
    static class ViewHolder {
         TextView text1;
         TextView text2;
         TextView longtext;
    }

    public View getView(int position, View convertView, ViewGroup parent) {

         Log.d(TAG, "position=" + position);

         ViewHolder holder;

         if (convertView == null) {
               convertView = mInflater.inflate(R.layout.list_item, parent, false);
               holder = new ViewHolder();
               holder.text1 = (TextView) convertView.findViewById(R.id.text1);
               holder.text2 = (TextView) convertView.findViewById(R.id.text2);
               holder.longtext = (TextView) convertView.findViewById(R.id.longtext);
               convertView.setTag(holder);
         } else {
               holder = (ViewHolder) convertView.getTag();
         }
 
         MyObj data = getItem(position);
         holder.text1.setText(data.text1);
         holder.text2.setText(data.text2);
         holder.longtext.setText(data.longText);
         
         return convertView;
   }
}

<RelativeLayout 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"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.settagandgettag.MainActivity" >

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="" />

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/textView1"
        android:layout_marginTop="120dp"
        android:layout_toRightOf="@+id/textView1"
        android:text="Button" />

</RelativeLayout>

package com.example.settagandgettag;

import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;

import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends ActionBarActivity {

    Button btn =null;
    TextView tv = null;
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        tv = (TextView)findViewById(R.id.textView1);
        btn =(Button)findViewById(R.id.button1);
        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                MyObject obj = new MyObject();
                obj.str="str before change";
                tv.setTag(obj);
                Log.v("#1", ((MyObject)tv.getTag()).str);
                
                obj.str="str after change";
                Log.v("#2", ((MyObject)tv.getTag()).str);
            }
        });
    
    }

    public class MyObject{
        public String str = "";
        
    }
    
    
    
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }
}