Android Handler 用法

Android handler
根据Android API DOC:Android Handler主要用于发送和处理和一个线程有关联的消息队列（MessageQueue）的消息和可运行对象。从这句话中可以知道Handler发送和处理的对象有两个：Message 和 Runnable对象。每个Handler实例和一个线程和这个线程的消息队列相关联。当然队列的特点就是先进先出的原则。
有下面的例子说明处理的它的两个操作对象：

package com.daisy.android.network;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ProgressBar;
import android.widget.TextView;

/**
 *@author Andrew.Lee
 *@create 2011-6-7 下午02:23:11
 *@version 1.0
 *@see
 */

public class HandlerActivity extends Activity implements OnClickListener {
	private static String TAG = "System.out";
	private Button start;
	private Button end;
	private ProgressBar progress;
	private Button progress_button;
	private Button progress_pause;
	private Handler handler;
	private Myhandler Myhandler;
	private boolean threadTerminal = false;
	private EditText editText;
	private TextView textView;

	public void onCreate(Bundle bundle) {
		super.onCreate(bundle);
		setContentView(R.layout.handler);
		findView();
		// define a handler
		handler = new Handler();
		// Output Acitvity thread info
		Log.i(TAG, "Activity Thread id:" + Thread.currentThread().getId());
		Log.i(TAG, "Activity Thread name:" + Thread.currentThread().getName());

	}

	public void findView() {
		editText = (EditText) findViewById(R.id.entry);

		start = (Button) findViewById(R.id.start);
		start.setOnClickListener(this);

		end = (Button) findViewById(R.id.end);
		end.setOnClickListener(this);
		progress = (ProgressBar) findViewById(R.id.progress);

		progress_button = (Button) findViewById(R.id.progress_button);
		progress_button.setOnClickListener(this);

		progress_pause = (Button) findViewById(R.id.pause);
		progress_pause.setOnClickListener(this);

		textView = (TextView) findViewById(R.id.display);

	}

	class Myhandler extends Handler {
		public void handleMessage(Message msg) {
			Log.i(TAG, "Handler process...");
			Log.i(TAG, "Handler Thread id:" + Thread.currentThread().getId());
			Log.i(TAG, "Handler Thread name:"
					+ Thread.currentThread().getName());
			int count = msg.getData().getInt("count");
			String str = msg.getData().getString("display");
			if (count <= 100)
				progress.setProgress(count);
			else
				progress.setVisibility(View.GONE);
			Log.i(TAG, "Handler Thread ---(##)---" + str);
			textView.setText("Handler Thread ---(##)---" + str);
		}

	}

	@Override
	public void onClick(View v) {
		// TODO Auto-generated method stub
		int id = v.getId();
		switch (id) {
		case R.id.start:
			Log.i(TAG, "You just press the start button");
			// associate with the runnable r, create runnable and add into the
			// message queue
			handler.post(r);
			break;
		case R.id.end:
			Log.i(TAG, "You just press the end button");
			// associate with the runnable r, remove the pending posts in the
			// message queue
			handler.removeCallbacks(r);
			break;
		case R.id.progress_button:
			Log.i(TAG, "You just click the progress button");
			progress.setVisibility(View.VISIBLE);
			Myhandler = new Myhandler();
			if (!threadTerminal && !handelrThread.isAlive())
				handelrThread.start();
			break;
		default:
			Log.i(TAG, "You just ...");

		}
	}

	Thread handelrThread = new Thread() {
		int count = 0;

		@Override
		public void run() {
			// TODO Auto-generated method stub
			Log.i(TAG, "Start the thread...");
			Log.i(TAG, "HandlerThread Thread id:"
					+ Thread.currentThread().getId());
			Log.i(TAG, "HandlerThread Thread name:"
					+ Thread.currentThread().getName());
			while (count < 101) {
				try {
					sleep(2000);
				} catch (InterruptedException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}

				count += 10;
				Message msg = new Message();
				Bundle bundle = new Bundle();
				bundle.putInt("count", count);
				bundle.putString("display", editText.getText().toString());
				msg.setData(bundle);
				Myhandler.sendMessage(msg);
				Log.i(TAG, "the count is :" + count);
			}
			threadTerminal = true;
		}
	};

	Runnable r = new Runnable() {

		@Override
		public void run() {
			// post after delay 3 seconds
			Log.i(TAG, "update for every 3 seconds");
			// Output Runnable thread info
			Log.i(TAG, "Runnable Thread id:" + Thread.currentThread().getId());
			Log.i(TAG, "Runnable Thread name:"
					+ Thread.currentThread().getName());
			textView.setText("Text ---(^o^)---Runnable:"
					+ editText.getText().toString());
			handler.postDelayed(r, 3000);
		}

	};

}

上面的例子部分引用 http://www.iteye.com/topic/1062942
使用Start-end button 来说明对Runnable对象的处理和操作
使用ProgressBar 来说明对消息Message的发送和处理。
从上面的例子中发现：
1. Activity、Runnable r、handler 和 Myhandler 都是运行在Activity 主线程中，所以他们都可以对Activity中的UI组件进行设置操作。
2. handelrThread 不是在主线程中，它只能获取UI组件的信息，但是不能对UI组件进行Set操作，或者布局的处理。