Looper thread的应用实例

创建一个有looper的thread，然后由主线程向其发信息。

public class TestLooperActivity extends Activity {
    
    Runnable ra;
    TextView tv;
    LooperThread lt;
    Context context;
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        context = this;
        Button btn = (Button)this.findViewById(R.id.button1);
        
        lt = new LooperThread();
        
        btn.setOnClickListener(new OnClickListener(){

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                lt.mHandler.sendEmptyMessage(10);
            }
        });
        
        lt.start();
    }
    
    class LooperThread extends Thread {
        public Handler mHandler;

        public void run() {
            Looper.prepare();

            mHandler = new Handler() {
                public void handleMessage(Message msg) {
                    // process incoming messages here
                    if (msg.what == 10) {
                        Toast.makeText(context, "Looper worked!!", Toast.LENGTH_LONG).show();
                    }
                }
            };

            Looper.loop();
        }
    }
}

－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－
转载自：http://stackoverflow.com/questions/4838207/how-to-create-a-looper-thread-then-send-it-a-message-immediately

Eventual solution (minus error checking), thanks to CommonsWare:

class Worker extends HandlerThread {

    // ...

    public synchronized void waitUntilReady() {
        d_handler = new Handler(getLooper(), d_messageHandler);
    }

}

And from the main thread:

Worker worker = new Worker();
worker.start();
worker.waitUntilReady(); // <- ADDED
worker.handler.sendMessage(...);

This works thanks to the semantics of HandlerThread.getLooper() which blocks until the looper has been initialized.

Incidentally, this is similar to my solution #1 above, since the HandlerThread is implemented roughly as follows (gotta love open source):

public void run() {
    Looper.prepare();
    synchronized (this) {
        mLooper = Looper.myLooper();
        notifyAll();
    }
    Looper.loop();
}

public Looper getLooper() {
    synchronized (this) {
        while (mLooper == null) {
            try {
                wait();
            } catch (InterruptedException e) {
            }
        }
    }
    return mLooper;
}

The key difference is that it doesn't check whether the worker thread is running, but that it has actually created a looper; and the way to do so is to store the looper in a private field. Nice!