public void run() {
  synchronized (mLock) {
    Looper.prepare();
    //do something
  }
  Looper.loop();
}

class myThread extends Thread{
   private EHandler mHandler ;
   public void run() {
     Looper myLooper, mainLooper;
     myLooper = Looper.myLooper ();
    mainLooper = Looper.getMainLooper ();
    String obj;
    if (myLooper == null ){
         mHandler = new EHandler(mainLooper);
         obj = "current thread has no looper!" ;
    }
    else {
       mHandler = new EHandler(myLooper);
       obj = "This is from current thread." ;
    }
    mHandler .removeMessages(0);
    Message m = mHandler .obtainMessage(1, 1, 1, obj);
    mHandler .sendMessage(m);
   }
}

public void handleMessage(Message msg)

// class ac01 extends Activity {
 // ………
   public void onClick(View v) {
       switch (v.getId()){
       case 101:
             t = new myThread();
          t .start();
         break ;
       case 102:
     finish();
            break ;
       }
  }
//------------------------------------------------------
class EHandler extends Handler {
      public EHandler(Looper looper) {
        super (looper);
      }
      @Override
      public void handleMessage(Message msg) {
       tv .setText((String)msg. obj );
    }
  }
//------------------------------------------------------
class myThread extends Thread{
   private EHandler mHandler ;
   public void run() {
    Looper myLooper, mainLooper;
    myLooper = Looper.myLooper ();
    mainLooper = Looper.getMainLooper ();
    String obj;
    if (myLooper == null ){
        mHandler = new EHandler(mainLooper);
        obj = "current thread has no looper!" ;
    }
    else {
       mHandler = new EHandler(myLooper);
       obj = "This is from current thread." ;
    }
    mHandler .removeMessages(0);
    Message m = mHandler .obtainMessage(1, 1, 1, obj);
    mHandler .sendMessage(m);
   }
 }
}

Looper myLooper, mainLooper;
myLooper = Looper.myLooper (); //很明显这个会返回空，因为你还没有 prepare，不会返回Looper。
mainLooper = Looper.getMainLooper ();

mAlbumArtWorker = new Worker("album art worker");
mAlbumArtHandler = new AlbumArtHandler(mAlbumArtWorker.getLooper());

private class Worker implements Runnable {
    private final Object mLock = new Object();
    private Looper mLooper;
    /**
     * Creates a worker thread with the given name. The thread
     * then runs a {@link android.os.Looper}.
     * @param name A name for the new thread
     */
    Worker(String name) {
      Thread t = new Thread(null, this, name);
      t.setPriority(Thread.MIN_PRIORITY);
      t.start();
      synchronized (mLock) {
        while (mLooper == null) {
          try {
            mLock.wait();
          } catch (InterruptedException ex) {
          }
        }
      }
    }
    public Looper getLooper() {
      return mLooper;
    }
    public void run() {
      synchronized (mLock) {
        Looper.prepare();
        mLooper = Looper.myLooper();
        mLock.notifyAll();
      }
      Looper.loop();
    }
    public void quit() {
      mLooper.quit();
    }
}

synchronized (mLock) {
    while (mLooper == null) {
      try {
        mLock.wait();
      } catch (InterruptedException ex) {
      }
    }
}

mAlbumArtWorker = new Worker("album art worker");