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