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