android TimerTask 的簡單應用

android應用開發中常常會用到定時器，不可避免的需要用到 TimerTask 定時器任務這個類
下面簡單的一個樣本示範了如何使用TimerTask

這個樣本示範了3秒未有觸屏事件發生則鎖屏（只是設定下文本，意思一下）有觸屏事件則解除鎖定

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();  //將原任務從隊列中移除
      }


      mTimerTask = new MyTimerTask();  // 建立一個任務      
      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();
  }

    }
}

這裡需要注意兩個問題：

  if (mTimerTask != null){
           mTimerTask.cancel();  //將原任務從隊列中移除
      }

每次放定時任務前，確保之前任務已從定時器隊列中移除

 mTimerTask = new MyTimerTask();  // 建立一個任務      

每次放任務都要建立一個對象，否則出現一下錯誤：
      ERROR/AndroidRuntime(11761): java.lang.IllegalStateException: TimerTask is scheduled already
      所以同一個定時器任務只能被放置一次