怎么在notifications中实现恢复activity，而不是开启一个新的activity

        long when = System.currentTimeMillis();
        Notification notification = new Notification(R.drawable.mark,"", when);
        notification.flags |= Notification.FLAG_NO_CLEAR|Notification.FLAG_ONGOING_EVENT;    
        
        Intent notificationIntent = new Intent(Intent.ACTION_MAIN);
        notificationIntent.setClass(this, MainActivity.class);
        notificationIntent.addCategory(Intent.CATEGORY_HOME);
        notificationIntent.addFlags(Intent.action_)
             notificationIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
             PendingIntent contentIntent = PendingIntent.getActivity(this,1,
                notificationIntent,PendingIntent.FLAG_UPDATE_CURRENT);

        
        notification.setLatestEventInfo(this,getResources().getString(R.string.app_name),"xxxxxx",contentIntent);            
        
        mNotificationManager.notify(R.drawable.mark, notification);