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
来源:https://www.cnblogs.com/ccdc/p/3837883.html