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Android线程通信

摘要

  andriod提供了 Handler 和 Looper 来满足线程间的通信。例如一个子线程从网络上下载了一副图片,当它下载完成后会发送消息给主线程,这个消息是通过绑定在主线程的Handler来传递的。

 

正文

图解:

代码示例:

/** * @author allin.dev *         http://allin.cnblogs.com */public class MainThread extends Activity{    private static final String TAG = "MainThread";  private Handler mMainHandler, mChildHandler;  private TextView info;  private Button msgBtn;    @Override  public void onCreate( Bundle savedInstanceState )  {    super.onCreate( savedInstanceState );    setContentView( R.layout.main );        info = (TextView) findViewById( R.id.info );    msgBtn = (Button) findViewById( R.id.msgBtn );        mMainHandler = new Handler( )    {            @Override      public void handleMessage( Message msg )      {        Log.i( TAG, "Got an incoming message from the child thread - "            + (String) msg.obj );        // 接收子线程的消息        info.setText( (String) msg.obj );      }          };        new ChildThread( ).start( );        msgBtn.setOnClickListener( new OnClickListener( )    {            @Override      public void onClick( View v )      {                if ( mChildHandler != null )        {                    // 发送消息给子线程          Message childMsg = mChildHandler.obtainMessage( );          childMsg.obj = mMainHandler.getLooper( ).getThread( ).getName( )              + " says Hello";          mChildHandler.sendMessage( childMsg );                    Log.i( TAG, "Send a message to the child thread - "              + (String) childMsg.obj );                  }      }    } );      }    public void onDestroy() {      super.onDestroy();    Log.i(TAG, "Stop looping the child thread‘s message queue");    mChildHandler.getLooper().quit();  }    class ChildThread extends Thread  {        private static final String CHILD_TAG = "ChildThread";        public void run( )    {      this.setName( "ChildThread" );            // 初始化消息循环队列,需要在Handler创建之前      Looper.prepare( );            mChildHandler = new Handler( )      {        @Override        public void handleMessage( Message msg )        {          Log.i( CHILD_TAG, "Got an incoming message from the main thread - "              + (String) msg.obj );                    try          {                        // 在子线程中可以做一些耗时的工作            sleep( 100 );                        Message toMain = mMainHandler.obtainMessage( );            toMain.obj = "This is " + this.getLooper( ).getThread( ).getName( )                + ".  Did you send me \"" + (String) msg.obj + "\"?";                        mMainHandler.sendMessage( toMain );                        Log.i( CHILD_TAG, "Send a message to the main thread - "                + (String) toMain.obj );                      }          catch ( InterruptedException e )          {            // TODO Auto-generated catch block            e.printStackTrace( );          }        }              };            Log.i( CHILD_TAG, "Child handler is bound to - "          + mChildHandler.getLooper( ).getThread( ).getName( ) );            // 启动子线程消息循环队列      Looper.loop( );    }  }}

 ps:

使用HandlerThread的looper对象创建Handler,如果使用默认的构造方法,很有可能阻塞UI线程,参考http://www.cnblogs.com/ccdc/p/3837798.html。改进方案新开一个线程将主线程的handler使用新开线程的looper替代主线程looper,示意图如下,

 

参考

shangdawei.android 线程间通信[2014-07-11](2013-03-26).http://www.cnblogs.com/shangdawei/archive/2013/03/26/2983217.html