android handler 线程机制的研究

先来看一段代码：

package com.my;import android.app.Activity;import android.os.Bundle;import android.os.Handler;import android.os.Message;import android.util.Log;public class DemoActivity extends Activity{private final static int MESSAGE=1;Handler handler=new Handler(){@Overridepublic void handleMessage(Message msg){// TODO Auto-generated method stubsuper.handleMessage(msg);switch(msg.what){case MESSAGE:Log.e("222", Thread.currentThread().getId()+"--->"+Thread.currentThread().getName());}}};@Overrideprotected void onCreate(Bundle savedInstanceState){// TODO Auto-generated method stubsuper.onCreate(savedInstanceState);setContentView(R.layout.main);Log.e("111", Thread.currentThread().getId()+"--->"+Thread.currentThread().getName());Message msg=new Message();msg.what=MESSAGE;handler.sendMessage(msg);}}

在这段代码中打印出如下log：

可以看出，handler和主程序都运行在主线程里面，如果要想让handler运行在不同的线程里面，就需要重新启动一个线程，代码如下：

package com.my;import android.app.Activity;import android.os.Bundle;import android.os.Handler;import android.os.Message;import android.util.Log;public class DemoActivity extends Activity {private final static int MESSAGE = 1;Handler handler = new Handler(){@Overridepublic void handleMessage(Message msg){// TODO Auto-generated method stubsuper.handleMessage(msg);switch (msg.what){case MESSAGE:Thread thread = new Thread(new Runnable(){@Overridepublic void run(){// TODO Auto-generated method stubLog.e("333", Thread.currentThread().getId() + "--->"+ Thread.currentThread().getName());}});thread.start();Log.e("222", Thread.currentThread().getId() + "--->"+ Thread.currentThread().getName());}}};@Overrideprotected void onCreate(Bundle savedInstanceState){// TODO Auto-generated method stubsuper.onCreate(savedInstanceState);setContentView(R.layout.main);Log.e("111", Thread.currentThread().getId() + "--->"+ Thread.currentThread().getName());Message msg = new Message();msg.what = MESSAGE;handler.sendMessage(msg);}}

运行后的log如下：

从上面的demo可以很明显地看出handler是和主线程在同一个线程中运行的，要想让handler里面处理的内容在不同的线程中运行，那么只有重新启动一个线程，才可以做到。

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