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发表于 2011-11-27 14:43 |只看该作者 |倒序浏览

Timer 与 TimerTask

使用Timer和TimerTask可以将一个动作延迟一段时间执行，或者周期性的执行某项任务。延迟动作可以很方便的用Handler实现，没必要用Timer。使用Timer和TimerTask周期性的执行某项任务还是非常方便的，它们也是Java本身的特性，可参考文档 http://docs.oracle.com/javase/1.5.0/docs/api/java/util/Timer.html （这个要比Google的文档详细很多，包括schedule与scheduleAtFixedRate的区别，cancel与purge的作用，一目了然）。

Timer和TimerTask使用起来也很简单，先定义一个Timer和TimerTask，再调用Timer的schedule方法，并将TimerTask传进去就行了，schedule的方式有很多，这里只把它们简单的列在这里。其中schedule的参数period，都是相对task上一次开始执行时间的，而scheduleAtFixedRate的参数period是相对task第一次开始执行时间的。还可以参考文章： http://blog.csdn.net/weidan1121/article/details/527307

Java代码

1.void schedule(TimerTask task, Date time)
2. // Schedules the specified task for execution at the specified time.
3.void schedule(TimerTask task, Date firstTime, long period)
4. // Schedules the specified task for repeated fixed-delay execution, beginning at the specified time.
5.void schedule(TimerTask task, long delay)
6. // Schedules the specified task for execution after the specified delay.
7.void schedule(TimerTask task, long delay, long period)
8. // Schedules the specified task for repeated fixed-delay execution, beginning after the specified delay.
9.void scheduleAtFixedRate(TimerTask task, Date firstTime, long period)
10. // Schedules the specified task for repeated fixed-rate execution, beginning at the specified time.
11.void scheduleAtFixedRate(TimerTask task, long delay, long period)
12. // Schedules the specified task for repeated fixed-rate execution, beginning after the specified delay.
void schedule(TimerTask task, Date time)
// Schedules the specified task for execution at the specified time.
void schedule(TimerTask task, Date firstTime, long period)
// Schedules the specified task for repeated fixed-delay execution, beginning at the specified time.
void schedule(TimerTask task, long delay)
// Schedules the specified task for execution after the specified delay.
void schedule(TimerTask task, long delay, long period)
// Schedules the specified task for repeated fixed-delay execution, beginning after the specified delay.
void scheduleAtFixedRate(TimerTask task, Date firstTime, long period)
// Schedules the specified task for repeated fixed-rate execution, beginning at the specified time.
void scheduleAtFixedRate(TimerTask task, long delay, long period)
// Schedules the specified task for repeated fixed-rate execution, beginning after the specified delay.

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下面Java代码说明一下使用方法：

Java代码

1.package com.ipjmc.timer;
2.
3.import java.util.Date;
4.import java.util.Timer;
5.import java.util.TimerTask;
6.
7.import android.app.Activity;
8.import android.os.Bundle;
9.import android.util.Log;
10.import android.widget.SlidingDrawer;
11.
12.public class TimerDemoActivity extends Activity {
13.
14. private static final String TAG = "TimerDemo";
15. private Timer mTimer = new Timer();
16. private TimerTask mTask = new MyTimerTask("A");
17.
18. @Override
19. public void onCreate(Bundle savedInstanceState) {
20. super.onCreate(savedInstanceState);
21. setContentView(R.layout.main);
22.
23. Log.i(TAG, "UI -> " +Thread.currentThread().getId());
24.
25. new Timer().schedule(mTask, new Date());
26. mTimer.schedule(new MyTimerTask("B"), new Date());
27. mTimer.schedule(new MyTimerTask("C"), 2000);
28. }
29.
30. private class MyTimerTask extends TimerTask {
31.
32. private String mName;
33.
34. public MyTimerTask(String name) {
35. mName = name;
36. }
37.
38. @Override
39. public void run() {
40. // TODO Auto-generated method stub
41. try {
42. Thread.sleep(1000);
43. } catch (InterruptedException e) {
44. // TODO Auto-generated catch block
45. e.printStackTrace();
46. }
47. Log.i(TAG, mName + " -> " + Thread.currentThread().getId());
48. }
49. }
50.}
package com.ipjmc.timer;
import java.util.Date;
import java.util.Timer;
import java.util.TimerTask;
import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.widget.SlidingDrawer;
public class TimerDemoActivity extends Activity {
private static final String TAG = "TimerDemo";
private Timer mTimer = new Timer();
private TimerTask mTask = new MyTimerTask("A");
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Log.i(TAG, "UI -> " +Thread.currentThread().getId());
new Timer().schedule(mTask, new Date());
mTimer.schedule(new MyTimerTask("B"), new Date());
mTimer.schedule(new MyTimerTask("C"), 2000);
}
private class MyTimerTask extends TimerTask {
private String mName;
public MyTimerTask(String name) {
mName = name;
}
@Override
public void run() {
// TODO Auto-generated method stub
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Log.i(TAG, mName + " -> " + Thread.currentThread().getId());
}
}
}

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[size=medium] 需要注意的是：
1.每一个Timer会单独开启一个线程，Timer中的费时操作不会阻止UI，但要在TimerTask中进行UI操作的话，需要用Handler或Activity.runOnUiThread()方法。

2.每个TimerTask只能被schedule一次，第二次会抛出异常

Java代码

1.new Timer().schedule(mTask, new Date());
2. new Timer().schedule(mTask, new Date()); //E/AndroidRuntime(760): Caused by: java.lang.IllegalStateException: TimerTask is scheduled already
new Timer().schedule(mTask, new Date());
new Timer().schedule(mTask, new Date()); //E/AndroidRuntime(760): Caused by: java.lang.IllegalStateException: TimerTask is scheduled already
3.Timer一旦取消，那么它的线程也就没了（http://disanji.net/2011/04/28/android-timer-tutorial/），

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不能再在调用Timer的schedule系列函数了，否则会抛出异常。怎么办？再创建一个新的Timer。

android

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Timer 与 TimerTask [复制链接]