Android实现定时器的三种方法及详解

新建一个Thread，使用sleep()延时

new Thread(){
@Override
public void run() {
// TODO Auto-generated method stub
super.run();
// Use while to run consistently, use if to run once.
while (true) {
try {
sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
doSomething(); //TODO Something
}
}
}.start();

使用Handler的postDelayed()的方法

Handler handler = new Handler();
Runnable runnable=new Runnable() {
@Override
public void run() {
doSomething(); //TODO Something
handler.postDelayed(this,  5 * 1000); //Put the statment here to run consistently, remove it to run once 
}
};

handler.postDelayed(runnable,  5 * 1000); //Start Timer

Handler的postDelayed(Runnable r, long delayMillis)方法与postAtTime(Runnable r, long uptimeMillis)方法的区别： postDelayed是在延迟x秒后执行执行操作, postAtTime是在特定的时间XX:YY:ZZ.mmm进行执行操作。
注意事项：一般会使用如下代码进行handler的取消：

handler.removeCallbacks(runnable); //Stop Timer

但是当某些特定的时候，removeCallbacks()可能会失效。例如当Activity转入后台再转入前台之后，再调用removeCallbacks()方法，会发现runnable无法正确地从队列中被移除。原因是当Activity转入后台后，runnable仍旧在运行，但当Activity重新转入前台后，会重新定义Runnable runnable。因此之前在运行的runnable无法被正确移除。解决方法是将handler和runnable定义成静态的，JVM只会为静态变量分配一次内存。

static Handler handler = new Handler();  
static Runnable runnable = new Runnable() {  

    @Override  
    public void run() {  
        @Override
public void run() {
doSomething(); //TODO Something
handler.postDelayed(this,  5 * 1000); //Put the statment here to run consistently, remove it to run once 
}
    }  
};

设置Timer及TimerTask

private final Timer timer = new Timer(); 
private TimerTask task; 

task = new TimerTask() { 
    @Override 
    public void run() { 
        doSomething(); //TODO Something
    } 
}; 

timer.schedule(task, 5 * 1000, 5 * 1000);

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Android实现定时器的三种方法及详解

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