Android 主线程和线程之间相互发送消息

通过分析Activity源码，我们知道每个Activity都有一个Looper，所以主线程在接收Message是不需要调用Looper.prepare()和Looper.loop()，但是线程是不带Looper的，当线程要接收来自主线程的消息是就需要调用Looper.prepare()和Looper.loop()。以下我们将通过一个示例，讲述主线程和线程之间如何发送Message。

`01`	`import` `android.app.Activity;`

`02`	`import` `android.os.Bundle;`

`03`	`import` `android.os.Handler;`

`04`	`import` `android.os.Message;`

`05`	`import` `android.widget.Toast;`

06

07 /**

`08`	`* 这个类是主线程，它每隔两秒就发送一个Message给线程，线程收到Message后将发送一个Message给主线程，主线程收到Message后会将Message内容Toast出来。`

`09`	`* org.fneg.HandlerTestActivity.java`

`10`	`* Create at: 2012-6-4 下午9:39:19`

`11`	`* @author:feng`

`12`	`* Email:fengcunhan@gmail.com`

13 *

14 */

`15`	`public` `class` `HandlerTestActivity` `extends` `Activity {`

`16`	`private` `Handler uiHandler;`

`17`	`private` `ThreadWithLooper thread;`

`18`	`private` `Runnable showRunable;`

`19`	`@Override`

`20`	`public` `void` `onCreate(Bundle savedInstanceState) {`

`21`	`super.onCreate(savedInstanceState);`

`22`	`setContentView(R.layout.main);`

`23`	`uiHandler=new` `Handler(){`

`24`	`@Override`

`25`	`public` `void` `handleMessage(Message msg) {`

`26`	`switch(msg.what){`

`27`	`case` `Messages.MSG_HELLO:`

`28`	`Toast.makeText(HandlerTestActivity.this, (String)msg.obj, Toast.LENGTH_SHORT).show();`

29 break;

30

31 }

32 }

33 };

`34`	`thread=new` `ThreadWithLooper(uiHandler);`

35

`36`	`thread.start();`

`37`	`showRunable=new` `Runnable() {`

38

`39`	`@Override`

`40`	`public` `void` `run() {`

`41`	`//給线程发送一个Message`

`42`	`thread.getHandler().sendEmptyMessage(Messages.MSG_HELLO);`

`43`	`uiHandler.postDelayed(this,` `2*1000);`

44 }

45 };

`46`	`uiHandler.post(showRunable);`

47

48 }

49

`50`	`@Override`

`51`	`protected` `void` `onStop() {`

`52`	`super.onStop();`

`53`	`uiHandler.removeCallbacks(showRunable);`

54 }

55 }

`01`	`import` `android.os.Handler;`

`02`	`import` `android.os.Looper;`

`03`	`import` `android.os.Message;`

04

05 /**

`06`	`* 从线程发送消息到UI线程（主线程）`

`07`	`* org.fneg.ThreadWithLooper.java`

`08`	`* Create at: 2012-6-4 下午4:58:11`

`09`	`* @author:feng<br/>`

`10`	`* Email:fengcunhan@gmail.com`

11 *

12 */

`13`	`public` `class` `ThreadWithLooper` `extends` `Thread {`

`14`	`private` `Handler handler;`

15

`16`	`private` `Handler uiHandler;`

17

`18`	`public` `ThreadWithLooper(Handler mHandler){`

`19`	`this.uiHandler=mHandler;`

`20`	`//初始化Handler，接收到主线程发送过来的Message就回复一个Message给主线程，消息内容是一个字符串和当前时间`

`21`	`handler =new` `Handler(){`

22

`23`	`@Override`

`24`	`public` `void` `handleMessage(Message msg) {`

`25`	`switch(msg.what){`

`26`	`case` `Messages.MSG_HELLO:`

`27`	`Message message=new` `Message();`

`28`	`message.what=Messages.MSG_HELLO;`

`29`	`message.obj="Yes!I get a hello"+System.currentTimeMillis();`

`30`	`uiHandler.sendMessage(message);`

31 break;

32

33 }

34 }

35

36 };

37 }

38

`39`	`public` `Handler getHandler() {`

`40`	`return` `handler;`

41 }

42

`43`	`public` `void` `setHandler(Handler handler) {`

`44`	`this.handler = handler;`

45 }

46

`47`	`@Override`

`48`	`public` `void` `run() {`

`49`	`Looper.prepare();`

50

`51`	`Looper.loop();`

52 }

53

54

55 }

01 /**

02 *

`03`	`* org.fneg.Messages.java`

`04`	`* Create at: 2012-6-4 下午4:51:20`

`05`	`* @author:feng`

`06`	`* Email:fengcunhan@gmail.com`

07 *

08 */

`09`	`public` `class` `Messages {`

`10`	`public` `static` `final` `int` `MSG_HELLO=0X1;`

11 }

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