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()
	{

		@Override
		public void handleMessage(Message msg)
		{
			// TODO Auto-generated method stub
			super.handleMessage(msg);
			switch(msg.what)
			{
			case MESSAGE:
				Log.e("222", Thread.currentThread().getId()+"--->"+Thread.currentThread().getName());
			}
		}
		
	};
	
	@Override
	protected void onCreate(Bundle savedInstanceState)
	{
		// TODO Auto-generated method stub
		super.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()
	{

		@Override
		public void handleMessage(Message msg)
		{
			// TODO Auto-generated method stub
			super.handleMessage(msg);
			switch (msg.what)
			{
			case MESSAGE:
				Thread thread = new Thread(new Runnable()
				{

					@Override
					public void run()
					{
						// TODO Auto-generated method stub
						Log.e("333", Thread.currentThread().getId() + "--->"
								+ Thread.currentThread().getName());
					}
				});
				thread.start();
				Log.e("222", Thread.currentThread().getId() + "--->"
						+ Thread.currentThread().getName());
			}
		}

	};

	@Override
	protected void onCreate(Bundle savedInstanceState)
	{
		// TODO Auto-generated method stub
		super.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。