android下消息机制简介

MainActivity.java

package com.example.test;

import java.util.Date;
import java.util.Timer;
import java.util.TimerTask;

import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.app.Activity;
import android.view.Menu;
import android.widget.TextView;

public class MainActivity extends Activity {
private TextView tv_txt;
private Timer timer;
private TimerTask task;

//1.在主线程里面定义个消息处理器
private Handler handler = new Handler(){

@Override
public void handleMessage(Message msg) {
//3.如果主线程消息队列里面有消息 looper会把这个消息 交给 handler处理
long time = (Long) msg.obj;
tv_txt.setText("当前时间:"+new Date(time));
super.handleMessage(msg);
}

};

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

tv_txt = (TextView) findViewById(R.id.tv_txt);

timer = new Timer();
task = new TimerTask() {
@Override
public void run() {
//tv_txt.setText("gagagag");
//2.利用主线程的handler 把消息放在 主线程的消息队列里
Message msg = new Message();
msg.obj = System.currentTimeMillis();
handler.sendMessage(msg);
}
};
timer.schedule(task, 1000, 1000);

}

}