我们开启一个线程，线程每隔一秒发送一次消息，我们在消息中更新TextView上显示的时间就ok了。

首先我们在布局文件中放一个TextView用来显示时间，如下所示：

xmlns:android="http://schemas.android.com/apk/res/android"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:background="@android:color/white">

android:id="@+id/mytime"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:gravity="center"

android:textColor="@android:color/black"

android:textSize="36sp"/>

之后我们写一个线程，线程里面无限循环，每隔一秒发送一个消息,其中由Handler来处理显示的结果：

public class TimeThread extends Thread {

@Override

public void run () {

do {

try {

Thread.sleep(1000);

Message msg = new Message();

msg.what = msgKey1;

mHandler.sendMessage(msg);

}

catch (InterruptedException e) {

e.printStackTrace();

}

} while(true);

}

}

private Handler mHandler = new Handler() {

@Override

public void handleMessage (Message msg) {

super.handleMessage(msg);

switch (msg.what) {

case msgKey1:

long sysTime = System.currentTimeMillis();

CharSequence sysTimeStr = DateFormat.format("hh:mm:ss", sysTime);

mTime.setText(sysTimeStr);

break;

default:

break;

}

}

};

之后我们可以在Activity的onCreate方法中开启这个线程，这时我们可以看到一个数字时钟了：

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.time);

mTime = (TextView) findViewById(R.id.mytime);

new TimeThread().start();

}

整个Activity的代码：

package com.fermax.test;

import android.app.Activity;

import android.os.Bundle;

import android.os.Handler;

import android.os.Message;

import android.text.format.DateFormat;

import android.widget.TextView;

public class TestActivity extends Activity {

private static final int msgKey1 = 1;

private TextView mTime;

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.time);

mTime = (TextView) findViewById(R.id.mytime);

new TimeThread().start();

}

public class TimeThread extends Thread {

@Override

public void run () {

do {

try {

Thread.sleep(1000);

Message msg = new Message();

msg.what = msgKey1;

mHandler.sendMessage(msg);

}

catch (InterruptedException e) {

e.printStackTrace();

}

} while(true);

}

}

private Handler mHandler = new Handler() {

@Override

public void handleMessage (Message msg) {

super.handleMessage(msg);

switch (msg.what) {

case msgKey1:

long sysTime = System.currentTimeMillis();

CharSequence sysTimeStr = DateFormat.format("hh:mm:ss", sysTime);

mTime.setText(sysTimeStr);

break;

default:

break;

}

}

};

}