android TimerTask 的简单应用

android应用开发中常常会用到定时器，不可避免的需要用到 TimerTask 定时器任务这个类
下面简单的一个示例演示了如何使用TimerTask

这个示例演示了3秒未有触屏事件发生则锁屏（只是设置下文本，意思一下）有触屏事件则解除锁定

public class ColTimerTaskActivity extends Activity {
/** Called when the activity is first created. */

private final String TAG = "ColTimerTaskActivity";
private final int EVENT_LOCK_WINDOW = 0x100;

private TextView textView;
private Handler mHandler;
private Timer mTimer;
private MyTimerTask mTimerTask;

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

textView = (TextView)findViewById(R.id.textview);

mHandler = new Handler(){
public void handleMessage(Message message){
Log.i(TAG, "message what = " + message.what);
if (message.what == 0x100){
lockWindow();
}

}
};

mTimer = new Timer(true);

resumeWindow();

StartLockWindowTimer();
}

public boolean onTouchEvent(MotionEvent event)
{
// TODO Auto-generated method stub
resumeWindow();
StartLockWindowTimer();

return super.onTouchEvent(event);
}

public void resumeWindow(){
textView.setText("main window");

}

public void lockWindow(){
textView.setText("lock window");
}

public void StartLockWindowTimer(){
if (mTimer != null){
if (mTimerTask != null){
mTimerTask.cancel(); //将原任务从队列中移除
}


mTimerTask = new MyTimerTask(); // 新建一个任务
mTimer.schedule(mTimerTask, 3000);
}
}

class MyTimerTask extends TimerTask{
@Override
public void run() {
// TODO Auto-generated method stub
Log.i(TAG, "run...");
Message msg = mHandler.obtainMessage(EVENT_LOCK_WINDOW);
msg.sendToTarget();
}

}
}

这里需要注意两个问题：

if (mTimerTask != null){
mTimerTask.cancel(); //将原任务从队列中移除
}

每次放定时任务前，确保之前任务已从定时器队列中移除

mTimerTask = new MyTimerTask(); // 新建一个任务

每次放任务都要新建一个对象，否则出现一下错误：
      ERROR/AndroidRuntime(11761): java.lang.IllegalStateException: TimerTask is scheduled already
      所以同一个定时器任务只能被放置一次