public class MainActivity extends Activity implements OnClickListener {
  private static final int UPDATE_TEXT = 1;
  private Button send;
  private TextView tv;
  
  private Handler hd = new MyHandler();

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    send = (Button) findViewById(R.id.bt_sendMessage);
    tv = (TextView) findViewById(R.id.tv_text);
    send.setOnClickListener(this);
  }

  @Override
  public void onClick(View v) {
    switch (v.getId()) {
    case R.id.bt_sendMessage:
      new Thread(new Runnable() {
        @Override
        public void run() { //　新建一个线程，并新建一个Message的对象，是用Handler的对象发送这个Message
          Message msg = new Message();
          msg.what = UPDATE_TEXT; // 用户自定义的一个值，用于标识不同类型的消息
          hd.sendMessage(msg); // 发送消息
        }
      }).start();
      break;

    default:
      break;
    }
  }
  
  // 定义一个内部类继承自Handler，并且覆盖handleMessage方法用于处理子线程传过来的消息
  class MyHandler extends Handler{
    @Override
    public void handleMessage(Message msg) {
      super.handleMessage(msg);
      switch (msg.what) {
      case UPDATE_TEXT: // 接受到消息之后，对UI控件进行修改
        tv.setText("修改成功！");
        break;

      default:
        break;
      }
    }
  }
}