本文转自:http://www.cnblogs.com/keyindex/articles/1822463.html
前言
学习android一段时间了，为了进一步了解android的应用是如何设计开发的，决定详细研究几个开源的android应用。从一些开源应用中吸收点东西，一边进行量的积累，一边探索android的学习研究方向。这里我首先选择了jwood的Standup Timer 项目。本文将把研究的内容笔记整理，建立一个索引列表。
关键词
Android.os.Handler涉及较多的知识点，我把一些关键词列举在下面，将主要介绍Handler：
- android.os.Handler 、 android.os.Handler.Callback
- Looper、
- Threadle、Runnable
- Message、Message queue
android.os.Handler
Handler在android里负责发送和处理消息。它的主要用途有：
1）按计划发送消息或执行某个Runnanble(使用POST方法)；
2）从其他线程中发送来的消息放入消息队列中，避免线程冲突（常见于更新UI线程）
默认情况下，Handler接受的是当前线程下的消息循环实例（使用Handler(Looper looper)、Handler(Looper looper, Handler.Callback callback)可以指定线程），同时一个消息队列可以被当前线程中的多个对象进行分发、处理（在UI线程中，系统已经有一个Activity来处理了，你可以再起若干个Handler来处理）。在实例化Handler的时候，Looper可以是任意线程的，只要有Handler的指针，任何线程也都可以sendMessage。Handler对于Message的处理不是并发的。一个Looper 只有处理完一条Message才会读取下一条，所以消息的处理是阻塞形式的（handleMessage()方法里不应该有耗时操作，可以将耗时操作放在其他线程执行，操作完后发送Message（通过sendMessges方法）,然后由handleMessage()更新UI）。
倒计时程序
利用Timer 编写一个倒计时程序，程序使用Timer和TimerTask来完成倒计时，同时使用sendMessages方法发送消息，然后在HanleMessage里更新UI。
Activity布局：
<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"android:orientation="vertical"android:layout_width="fill_parent"android:layout_height="fill_parent"> <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:layout_gravity="center"android:id="@+id/txt"/> <Buttonandroid:id="@+id/btnStartTime"android:text="开始计时"android:layout_width="80dip"android:layout_height="wrap_content" ></Button><Buttonandroid:id="@+id/btnStopTime"android:text="停止计时"android:layout_width="80dip"android:layout_height="wrap_content"/><SeekBar android:id="@+id/SeekBar01" android:layout_width="match_parent" android:layout_height="wrap_content"></SeekBar> </LinearLayout>
@Overridepublicvoid onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.main);txt = (TextView) findViewById(R.id.txt);btnStart = (Button) findViewById(R.id.btnStartTime);btnStop = (Button) findViewById(R.id.btnStopTime);Log.d("ThreadId", "onCread:"+ String.valueOf(Thread.currentThread().getId()));myHandler =new Handler(this);btnStart.setOnClickListener(this);btnStop.setOnClickListener(this);}
在onCreate方法中初始化元素个元素，myHandler = new Handler(this); 调用的是 Handler(Handler.Callback callback)构造函数，在回调方法callback中对发送来的消息进行处理（这样我们就不必使用内部类的写法来 重写HandleMessage()方法了），因此Activity必须实现android.os.Handler.Callback 接口。我们还在将onCreate 方法的ThreadId 记录在了Log中用以和消息发送、处理时所作的线程进行比较。
发送消息@Overridepublicvoid onClick(View v) {switch (v.getId()) {case R.id.btnStartTime:startTimer();break;case R.id.btnStopTime:timer.cancel();break;}}privatesynchronizedvoid startTimer() {timer =new Timer();// TimerTask updateTimerValuesTask = new TimerTask() {// @Override// public void run() {// updateTimerValues();// }//// };//自定义的CallBack模式。Task继承自TimerTaskTask updateTimerValuesTask =new Task(this);timer.schedule(updateTimerValuesTask, 1000, 1000);}//执行耗时的倒计时任务。 privatevoid updateTimerValues() {total--;Log.d("ThreadId", "send:"+ String.valueOf(Thread.currentThread().getId()));Message msg=new Message();Bundle date =new Bundle();// 存放数据date.putInt("time", total);msg.setData(date);msg.what=0;myHandler.sendMessage(msg);//另一种写法 // Message msg=myHandler.obtainMessage(); // Bundle date = new Bundle();// 存放数据 // date.putInt("time", total); // msg.setData(date); // msg.what=0; // msg.sendToTarget(); }@Overridepublicvoid TaskRun() {updateTimerValues();}
ICallBack接口和Task类publicinterface ITaskCallBack {void TaskRun(); }publicclass Task extends TimerTask {private ITaskCallBack iTask;public Task(ITaskCallBack iTaskCallBack){super();iTask=iTaskCallBack;}publicvoid setCallBack(ITaskCallBack iTaskCallBack){iTask=iTaskCallBack;}@Overridepublicvoid run() {// TODO Auto-generated method stub iTask.TaskRun();}}
实现CallBack/*** 实现消息处理*/@Overridepublicboolean handleMessage(Message msg) {switch(msg.what){case0:Bundle date=msg.getData();txt.setText(String.valueOf(date.getInt("time")));Log.d("ThreadId", "HandlerMessage:"+ String.valueOf(Thread.currentThread().getId()));Log.d("ThreadId", "msgDate:"+ String.valueOf(date.getInt("time")));break;}returnfalse;}
可以看到 实现android.os.Handler.Callback 接口，其实就是对handleMessage（）方法进行重写（和内部类的一个区别是，内部类的返回值是Void）。
运行结果
可以看到在onCreate 方法中线程的ID是1（UI线程） 这与 HandlerMessage 进行消息处理时是所作的线程ID是一样的，而消息发送的线程ID则为8非UI线程。
使用Threadle进行实现
Activity类publicclass ThreadHandlerrActivity extends Activity implements Callback,OnClickListener {private TextView txt;private Button btnStart, btnStop;private Handler myHandler;private TimerThread timerThread;privateint Total=30;/** Called when the activity is first created. */@Overridepublicvoid onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.main);txt = (TextView) findViewById(R.id.txt);btnStart = (Button) findViewById(R.id.btnStartTime);btnStop = (Button) findViewById(R.id.btnStopTime);Log.d("ThreadId", "onCread:"+ String.valueOf(Thread.currentThread().getId()));myHandler =new Handler(this);btnStart.setOnClickListener(this);btnStop.setOnClickListener(this);}/*** 实现消息处理*/@Overridepublicboolean handleMessage(Message msg) {switch(msg.what){case0:Bundle date=msg.getData();txt.setText(String.valueOf(date.getInt("time")));Log.d("ThreadId", "HandlerMessage:"+ String.valueOf(Thread.currentThread().getId()));Log.d("ThreadId", "msgDate:"+ String.valueOf(date.getInt("time")));break;}returnfalse;}@Overridepublicvoid onClick(View v) {switch (v.getId()) {case R.id.btnStartTime://自定义的线程timerThread=new TimerThread(myHandler,60);timerThread.start();break;case R.id.btnStopTime:timerThread.stop();//timerThread.destroy(); break;}}}
自定义的线程类*** 自定义的线程类，通过传入的Handler,和Total 定期执行耗时操作* @author linzijun**/ publicclass TimerThread extends Thread {publicint Total=60;public Handler handler;/*** 初始化构造函数* @param mhandler handler 用于发送消息* @param total 总周期*/public TimerThread(Handler mhandler,int total){super();handler=mhandler;Total=total;}@Overridepublicvoid run() {while(true){Total--;if(Total<0)break;try {Thread.sleep(1000);} catch (InterruptedException e) {// TODO Auto-generated catch block e.printStackTrace();}Message msg=new Message();Bundle date =new Bundle();// 存放数据date.putInt("time", Total);msg.setData(date);msg.what=0;Log.d("ThreadId", "Thread:"+ String.valueOf(Thread.currentThread().getId()));handler.sendMessage(msg);}super.run();}}
关于POST
Post的各种方法是把一个Runnable发送给消息队列，它将在到达时进行处理。
POSTpublicclass PostHandler extends Activity implements OnClickListener, Runnable {private TextView txt;private Button btnStart, btnStop;private Handler myHandler;private Timer timer;privateint total =60;@Overrideprotectedvoid onCreate(Bundle savedInstanceState) {// TODO Auto-generated method stub super.onCreate(savedInstanceState);setContentView(R.layout.main);txt = (TextView) findViewById(R.id.txt);btnStart = (Button) findViewById(R.id.btnStartTime);btnStop = (Button) findViewById(R.id.btnStopTime);Log.d("ThreadId", "onCread:"+ String.valueOf(Thread.currentThread().getId()));myHandler =new Handler(){@Overridepublicvoid handleMessage(Message msg) {switch(msg.what){case0:Bundle date=msg.getData();txt.setText(String.valueOf(date.getInt("time")));Log.d("ThreadId", "HandlerMessage:"+ String.valueOf(Thread.currentThread().getId()));Log.d("ThreadId", "msgDate:"+ String.valueOf(date.getInt("time")));break;}}};btnStart.setOnClickListener(this);btnStop.setOnClickListener(this);}@Overridepublicvoid onClick(View v) {switch (v.getId()) {case R.id.btnStartTime://myHandler.post(this);myHandler.postDelayed(this, 1000);break;case R.id.btnStopTime:break;}}@Overridepublicvoid run() {while(true){total--;if(total<0)break;try {Thread.sleep(1000);} catch (InterruptedException e) {// TODO Auto-generated catch block e.printStackTrace();}Message msg=new Message();Bundle date =new Bundle();// 存放数据date.putInt("time", total);msg.setData(date);msg.what=0;Log.d("ThreadId", "POST:"+ String.valueOf(Thread.currentThread().getId()));myHandler.sendMessage(msg);Log.d("ThreadId", "Thread:"+ String.valueOf(Thread.currentThread().getId()));}}}
POSTpublicclass PostHandler extends Activity implements OnClickListener, Runnable {private TextView txt;private Button btnStart, btnStop;private Handler myHandler;private Timer timer;privateint total =60;@Overrideprotectedvoid onCreate(Bundle savedInstanceState) {// TODO Auto-generated method stub super.onCreate(savedInstanceState);setContentView(R.layout.main);txt = (TextView) findViewById(R.id.txt);btnStart = (Button) findViewById(R.id.btnStartTime);btnStop = (Button) findViewById(R.id.btnStopTime);Log.d("ThreadId", "onCread:"+ String.valueOf(Thread.currentThread().getId()));myHandler =new Handler(){@Overridepublicvoid handleMessage(Message msg) {switch(msg.what){case0:Bundle date=msg.getData();txt.setText(String.valueOf(date.getInt("time")));Log.d("ThreadId", "HandlerMessage:"+ String.valueOf(Thread.currentThread().getId()));Log.d("ThreadId", "msgDate:"+ String.valueOf(date.getInt("time")));break;}}};btnStart.setOnClickListener(this);btnStop.setOnClickListener(this);}@Overridepublicvoid onClick(View v) {switch (v.getId()) {case R.id.btnStartTime://myHandler.post(this);myHandler.postDelayed(this, 1000);break;case R.id.btnStopTime:break;}}@Overridepublicvoid run() {while(true){total--;if(total<0)break;try {Thread.sleep(1000);} catch (InterruptedException e) {// TODO Auto-generated catch block e.printStackTrace();}Message msg=new Message();Bundle date =new Bundle();// 存放数据date.putInt("time", total);msg.setData(date);msg.what=0;Log.d("ThreadId", "POST:"+ String.valueOf(Thread.currentThread().getId()));myHandler.sendMessage(msg);Log.d("ThreadId", "Thread:"+ String.valueOf(Thread.currentThread().getId()));}}}
参考文献
android学习笔记之消息机制，异步和多线程
android handler概念解释
SDK
