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 }
package com.example.fd;
import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ImageButton;
import android.widget.TextView;
import com.example.fd.R.id;
public class MainActivity extends Activity {
Handler mh;
TextView te;
Button bt1;
ImageButton bt2;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
te=(TextView)findViewById(id.textView1);
bt2=(ImageButton)findViewById(id.imageButton1);
bt1=(Button)findViewById(id.button1);
bt2.setOnClickListener(new OnClickListener(){
public void onClick(View v){
Runnable rn=new Runnable(){
public void run(){
te.setText("aaaaa");
}
};
Message ms=new Message();
ms.what=1;
mh.sendMessage(ms);
}
});
bt1.setOnClickListener(new OnClickListener(){
public void onClick(View v){
Runnable rn=new Runnable(){
public void run(){
te.setText("This is now Handler");
}
};
Message msg=new Message();
msg.what=2;
//mh.post(rn);
mh.sendMessage(msg);
}
});
mh=new Handler(){
public void handleMessage(Message msg){
switch (msg.what){
case 1:
te.setText("this is from Handler");
break;
case 2:
te.setText("This is from Hander 2");
break;
}
}
};
}
@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;
}
}