android TimerTask 的简单应用

清疚 2021-11-27 07:52 263阅读 0赞

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

[![复制代码][copycode.gif]][copycode.gif 1]

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();
      }
    
        }
    }

[![复制代码][copycode.gif]][copycode.gif 1]

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

转载于:https://www.cnblogs.com/hnrainll/archive/2012/05/24/2517080.html

[copycode.gif]: https://common.cnblogs.com/images/copycode.gif
[copycode.gif 1]: /images/20211126/a99ac256b923410b848ba656276cdecb.png