android TimerTask 的简单应用，以及java.lang.IllegalStateException: TimerTask is scheduled already错误的解决方法【转】

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, );
     }
    }

    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(): Java.lang.IllegalStateException: TimerTask is scheduled already

所以同一个定时器任务只能被放置一次