ERROR/AndroidRuntime(11761): java.lang.IllegalStateException: TimerTask is sche

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