android应用中怎么对UI进行异步更新

package com.example.runonuithreadtest;import android.app.Activity;import android.os.Bundle;import android.os.Handler;import android.widget.TextView;public class MainActivity extends Activity {  private TextView tv;  Handler handler = new Handler() {  public void handleMessage(android.os.Message msg) {   if(msg.what==0x123)   {    tv.setText("更新后的TextView");   }  }; };  @Override protected void onCreate(Bundle savedInstanceState) {  super.onCreate(savedInstanceState);  setContentView(R.layout.activity_main);  tv = (TextView) findViewById(R.id.tv);  new MyThread().start(); } class MyThread extends Thread {  @Override  public void run() {   //延迟两秒更新   try {    Thread.sleep(2000);   } catch (InterruptedException e) {    // TODO Auto-generated catch block    e.printStackTrace();   }   handler.sendEmptyMessage(0x123);  } }}