Android消息处理Handler,Message,Looper

MessageQueue

消息队列,存放消息的地方.每个线程只能拥有一个MessageQueue

Looper

Adnroid系统中的Looper负责管理线程的MessageQueue.除了主线程外,创建的线程默认是没有Looper和MessageQueue,创建一个Looper会同时创建一个MessageQueue,可以使用Looper.prepare()创建MessageQueue,Looper.loop()进入消息循环,Looper.release()释放资源.

class LooperThread extends Thread { public Handler mHandler; @Override public void run() { // 创建消息队列 Looper.prepare(); mHandler = new Handler() { public void handleMessage(android.os.Message msg) { // process incoming messages here } }; // 进入消息循环 Looper.loop(); super.run(); //释放资源，使用Looper.release方法。 } }

Message

消息对象,MessageQueue里存放的对象,可以调用removeMessages()时，将Message从Message Queue中删除和通过Handler对象的obtainMessage()获取一个Message实例,可以在线程中使用Handler对象的sendEmptyMessage()或者sendMessage()来传递Bundle对象到Handler,对Handler类提供handlerMessage(Message msg)判断,通过msg.what来区分每一条信息

Handler

Handler的作用是把消息加入特定的Looper消息队列中,并分发和处理该消息队列中的消息.如另一个线程怎样把消息放入主(UI)线程的消息队列,可以通过Handler对象,通过调用Handler主线程的sendMessage接口,把消息队列放入主线程的消息队列,并在该Handler的handleMessage()来处理消息

下面是模拟多线程并发的例子其中有用到当所有线程执行完毕更新UI需要Handler

/** Called when the activity is first created. */ private String URL = "http://www.baidu.com"; private int NUM = 100; private Button myButton; private EditText mEditTextURL, mEditTextNUM; private ProgressDialog pd; private static int count = 0; Handler myHandler = new Handler() { public void handleMessage(android.os.Message msg) { if (msg.what == 0) pd.dismiss(); super.handleMessage(msg); }; }; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); mEditTextURL = (EditText) findViewById(R.id.myEditTextURL); mEditTextNUM = (EditText) findViewById(R.id.myEditTextNUM); myButton = (Button) findViewById(R.id.myButton); myButton.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { // TODO Auto-generated method stub if (!mEditTextURL.getText().toString().trim().equals("")) URL = mEditTextURL.getText().toString().trim(); if (!mEditTextNUM.getText().toString().trim().equals("")) NUM = Integer.parseInt(mEditTextNUM.getText().toString() .trim()); pd = ProgressDialog.show(HttpTestActivity.this, "xxx","xxx..."); outFile(); for (int i = 0; i < NUM; i++) {

count++; new Thread(new Handl(i)).start(); } } }); } public void outFile() { PrintStream stream = null; try { File f = new File(Environment.getExternalStorageDirectory(), "xxx.txt"); if (!f.exists()) f.createNewFile(); stream = new PrintStream(f); System.setOut(stream); } catch (Exception e) { // TODO: handle exception e.printStackTrace(); } } class Handl implements Runnable { private int No; public Handl(int no) { this.No = no; } @Override public void run() { // TODO Auto-generated method stub Thread.currentThread().setName(No + ""); HttpClient httpClient = new DefaultHttpClient(); // 设置请求超时 httpClient.getParams().setParameter( CoreConnectionPNames.CONNECTION_TIMEOUT, 5000); // 设置读取超时 httpClient.getParams().setParameter( CoreConnectionPNames.SO_TIMEOUT, 3000); HttpGet get = new HttpGet(URL); String strResult = ""; try { HttpResponse response = httpClient.execute(get); if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) { strResult = EntityUtils.toString(response.getEntity()); System.out.println("ThreadID:" + Thread.currentThread().getName()); System.out.println(strResult); } else { System.out.println(Thread.currentThread().getName() + "请求失败"); } Thread.sleep((long) Math.random() * 1000); } catch (InterruptedException e) { // TODO: handle exception e.printStackTrace(); } catch (IOException e) { // TODO: handle exception e.printStackTrace(); } catch (Exception e) { // TODO: handle exception e.printStackTrace(); } finally { synchronized (this) { count--; } } Message message = new Message(); message.what = count; myHandler.sendMessage(message); }

消息的处理者，handler负责将需要传递的信息封装成Message，通过调用handler对象的obtainMessage()来实现； 将消息传递给Looper，这是通过handler对象的sendMessage()来实现的。继而由Looper将Message放入MessageQueue中。 当Looper对象看到MessageQueue中含有Message，就将其广播出去。该handler对象收到该消息后，调用相应的handler对象的handleMessage()方法 对其进行处理。

更多参考:

倒计时程序

线程之间的消息传递