Handler 简单介绍

简单点说，哪个线程new Handler（）了当前这个对象，handerl就会处理哪个线程。
所以，android UI线程里创建了一个Handler，再用次handler来更改UI，就会没有问题额。

 1 package com.example.fd;
 2 
 3 import android.app.Activity;
 4 import android.os.Bundle;
 5 import android.os.Handler;
 6 import android.os.Message;
 7 import android.view.Menu;
 8 import android.view.View;
 9 import android.view.View.OnClickListener;
10 import android.widget.Button;
11 import android.widget.ImageButton;
12 import android.widget.TextView;
13 
14 import com.example.fd.R.id;
15 
16 public class MainActivity extends Activity {
17     Handler mh;
18     TextView te;
19     Button bt1;
20     ImageButton bt2;
21     @Override
22     protected void onCreate(Bundle savedInstanceState) {
23         super.onCreate(savedInstanceState);
24         setContentView(R.layout.activity_main);
25         te=(TextView)findViewById(id.textView1);
26         bt2=(ImageButton)findViewById(id.imageButton1);
27         bt1=(Button)findViewById(id.button1);
28         bt2.setOnClickListener(new OnClickListener(){
29             public void onClick(View v){
30                 Runnable rn=new Runnable(){
31                     public void run(){
32                         te.setText("aaaaa");
33                     }
34                 };
35                 Message ms=new Message();
36                 ms.what=1;
37                 mh.sendMessage(ms);
38             }
39         });
40         bt1.setOnClickListener(new OnClickListener(){
41             public void onClick(View v){
42                 Runnable rn=new Runnable(){
43                     public void run(){
44                         te.setText("This is now Handler");
45                     }
46                 };
47                 Message msg=new Message();
48                 msg.what=2;
49                 //mh.post(rn);
50                 mh.sendMessage(msg);
51             }
52         });
53         mh=new Handler(){
54             public void handleMessage(Message msg){
55                 switch (msg.what){
56                     case 1:
57                         te.setText("this is from Handler");
58                         break;
59                     case 2:
60                         te.setText("This is from Hander 2");
61                         break;
62                         
63                 }
64             }
65         };
66         
67     }
68 
69 
70     @Override
71     public boolean onCreateOptionsMenu(Menu menu) {
72         // Inflate the menu; this adds items to the action bar if it is present.
73         getMenuInflater().inflate(R.menu.main, menu);
74         return true;
75     }
76     
77 }