1. 一个有趣Demo:

(1)定义一个handler变量

    private final Handler mHandler = new Handler();

(2)定义一个Runnable变量

private Runnable onDoSomethingRunnable = new Runnable() {

	public void run() {

		onDoSomething();

	}

};

(3)定义onDoSomething()方法：

public void onDoSomething(){

    ..................................

    ..................................

    mHandler.postDelayed(onDoSomethingRunnable,150);

}

大家看一下上面的代码，发现了什么没。对，这个组合，可以 实现每隔一段时间，循环的执行某个操作。eg:每隔一秒，更新UI，每隔一段时间，去查看一个进程或者服务是否结束，............等等.当然了，大家可能会发现，一种方式可能有点消耗资源，因为他会循环的执行固定的操作，所以一般还是少用。

2. 一些关于Handler的事情：

A Handler allows you to send and process Message and Runnable objects associated with athread's MessageQueue

handler的作用，我就不说了，这种机制，我的理解是将一些非主UI线程更新UI，传递一些数据等等。当然，官方的说明：

There are two main uses for a Handler: (1) to schedule messages and runnablesto be executed as some point in the future; and (2) to enqueue anactionto be performed on a different thread than your own.

Handler中分发消息和runnable的一些方法:

post(Runnable),postAtTime(Runnable, long),postDelayed(Runnable, long),

sendEmptyMessage(int),sendMessage(Message),sendMessageAtTime(Message, long),sendMessageDelayed(Message, long)

Handler删除消息和runnable的方法：

removeCallbacks(Runnable)， removeCallbacks(Runnable, Object )， removeCallbacksAndMessages(Object)，

removeMessages(int)，  removeMessages(int , Object )

3.几个经典的DEMO。

(1)在一段数据处理的耗时操作后，如果这个操作超过1s，就显示进度条，如果耗时操作不超过1s，则不显示进度条后

//Handler处理消息

final Handler handler = new Handler();

final ProgressDialog progressDialog = new ProgressDialog(this);

progressDialog.setMessage(getText(R.string.adding_recipients));

progressDialog.setIndeterminate(true);

progressDialog.setCancelable(false);

final Runnable showProgress = new Runnable() {

	public void run() {

		progressDialog.show();

	}

};

// Only show the progress dialog if we can not finish off parsing the return data in 1s,

// otherwise the dialog could flicker.

handler.postDelayed(showProgress, 1000);

new Thread(new Runnable() {

	public void run() {

	   try {

               //数据处理

           } finally {

		handler.removeCallbacks(showProgress);

		progressDialog.dismiss();

           }

	}

}).start();

(2)更新UI界面

在需要更新页面的地方，发出更新界面的命令

private static final int UPDATE_PAGE_INDICATOR  = 1;

/****更新用户选中的数目******/

private static final int UPDATE_SELE_COUNT  = 2;

/****更新页面指示器******/

Message msg = myHandler.obtainMessage();

Bundle bundle = new Bundle();

//bundle.putInt("page", page);

bundle.putInt("page", PageCurrent);

msg.setData(bundle);    // 向消息中添加数据

msg.what = UPDATE_PAGE_INDICATOR;

myHandler.sendMessage(msg);    // 向Handler发送消息，更新UI  

在需要更新指示选中数目的TextView的地方，发出更新界面的命令

myHandler.sendEmptyMessage(UPDATE_SELE_COUNT);	

更新界面的操作，都放在myHandler 中

/***********myHandler：更新界面***********/

public Handler myHandler = new Handler(){

	public void handleMessage(Message msg) {

		super.handleMessage(msg);

switch(msg.what)

		{

		case  UPDATE_PAGE_INDICATOR :

			Bundle data = msg.getData();

			int page = (Integer) data.get("page");

			/*****更新页面指示器******/

			upDatePageIndicator(page);

			break;

		case UPDATE_SELE_COUNT:

			mySelectCount.setText(""+selectCount);

			break;

		}

	}

};

(3).Handler 和 Runnable 控制显示一个文本,1.5s后，让其不显示：

private TextView overlay = null;

LayoutInflater inflater = LayoutInflater.from(this);

overlay = (TextView) inflater.inflate(R.layout.overlay, null);  

private Handler <strong>handler</strong>;

handler = new Handler();

private OverlayThread <strong>overlayThread</strong>;

overlayThread = new OverlayThread();

overlay.setText(sections[position]);

overlay.setVisibility(View.VISIBLE);

<strong>handler.removeCallbacks(overlayThread);

/*****延迟一秒后执行，让overlay为不可见*****/

handler.postDelayed(overlayThread, 1500);</strong>

/**

* 类描述：OverlayThread：实现设置overlay不可见

*  @author hexiaoming

*  @version

*/

private class OverlayThread implements Runnable {

/**

* 方法描述：run方法

* @param

* @return

* @see OverlayThread

*/

public void run() {

	overlay.setVisibility(View.GONE);

}

}

参考资料：

1.Android的Handler总结

http://www.cnblogs.com/dawei/archive/2011/04/09/2010259.html