Android TimerTask 的简单应用及注意事项
Android TimerTask 的简单应用及注意事项
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
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