handler——handler的使用例子

转自http://blog.csdn.net/fdaopeng/article/details/7863840

Android UI操作并不是线程安全的，所以无法在子线程中更新UI。但Andriod提供了几种方法，可以在子线程中通知UI线程更新界面：

    Activity.runOnUiThread( Runnable )
    View.post( Runnable )
    View.postDelayed( Runnable, long )
    Handler 

 比较常用的是通过Handler，用Handler来接收子线程发送的数据，并用此数据配合主线程更新UI。那么，只要在主线程中创建Handler对象，在子线程中调用Handler的sendMessage方法，就会把消息放入主线程的消息队列，并且将会在Handler主线程中调用该handler的handleMessage方法来处理消息。 

    package com.superonion;   
      
    import android.app.Activity;   
    import android.os.Bundle;   
    import android.os.Message;   
    import android.util.Log;   
    import android.os.Handler;   
      
    public class MyHandler extends Activity {   
        static final String TAG = "Handler";   
        Handler h = new Handler(){   
            public void handleMessage (Message msg)   
            {   
                switch(msg.what)   
                {   
                case HANDLER_TEST:   
                    Log.d(TAG, "The handler thread id = " + Thread.currentThread().getId() + "\n");   
                    break;   
                }   
            }   
        };   
      
        static final int HANDLER_TEST = 1;   
        /** Called when the activity is first created. */  
        @Override  
        public void onCreate(Bundle savedInstanceState) {   
            super.onCreate(savedInstanceState);   
            Log.d(TAG, "The main thread id = " + Thread.currentThread().getId() + "\n");   
      
            new myThread().start();   
            setContentView(R.layout.main);   
        }   
      
        class myThread extends Thread   
        {   
            public void run()   
            {   
                Message msg = new Message();   
                msg.what = HANDLER_TEST;   
                h.sendMessage(msg);   
                Log.d(TAG, "The worker thread id = " + Thread.currentThread().getId() + "\n");   
            }   
        }   
    }  

 以上代码中，Handler在主线程中创建后，子线程通过 sendMessage()方法就可以将消息发送到主线程中，并在handleMessage()方法中处理。