public class MainActivity extends Activity implements View.OnClickListener {
  private TextView stateText;
  private Button btn;
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    stateText = (TextView) findViewById(R.id.tv);
    btn = (Button) findViewById(R.id.btn);
    btn.setOnClickListener(this);
  }
  @Override
  public void onClick(View v) {
    new WorkThread().start();
  }
  //工作线程
  private class WorkThread extends Thread {
    @Override
    public void run() {
      //......处理比较耗时的操作
      //处理完成后改变状态
      stateText.setText("completed");
    }
  }
}

public class MainActivity extends Activity implements View.OnClickListener {
  private static final int COMPLETED = 0;
  private TextView stateText;
  private Button btn;
  private Handler handler = new Handler() {
    @Override
    public void handleMessage(Message msg) {
      if (msg.what == COMPLETED) {
        stateText.setText("completed");
      }
    }
  };
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    stateText = (TextView) findViewById(R.id.tv);
    btn = (Button) findViewById(R.id.btn);
    btn.setOnClickListener(this);
  }
  @Override
  public void onClick(View v) {
    new WorkThread().start();
  }
  //工作线程
  private class WorkThread extends Thread {
    @Override
    public void run() {
      //......处理比较耗时的操作
      //处理完成后给handler发送消息
      Message msg = new Message();
      msg.what = COMPLETED;
      handler.sendMessage(msg);
    }
  }
}

class WorkThread extends Thread {
   public Handler mHandler;
   public void run() {
     Looper.prepare();
     mHandler = new Handler() {
       public void handleMessage(Message msg) {
         // 处理收到的消息
       }
     };
     Looper.loop();
   }
}

/**
* Default constructor associates this handler with the queue for the
* current thread.
*
* If there isn't one, this handler won't be able to receive messages.
*/
public Handler() {
    if (FIND_POTENTIAL_LEAKS) {
      final Class<? extends Handler> klass = getClass();
      if ((klass.isAnonymousClass() || klass.isMemberClass() || klass.isLocalClass()) &&
          (klass.getModifiers() & Modifier.STATIC) == 0) {
        Log.w(TAG, "The following Handler class should be static or leaks might occur: " +
          klass.getCanonicalName());
      }
    }
    mLooper = Looper.myLooper();
    if (mLooper == null) {
      throw new RuntimeException(
        "Can't create handler inside thread that has not called Looper.prepare()");
    }
    mQueue = mLooper.mQueue;
    mCallback = null;
}
/**
* Use the provided queue instead of the default one.
*/
public Handler(Looper looper) {
    mLooper = looper;
    mQueue = looper.mQueue;
    mCallback = null;
}