解決iOS程式UI主線程和定時器相互阻塞的問題

此文是接上文http://www.cnblogs.com/zzltjnh/archive/2013/05/15/3080058.html問題解決之後遇到的一個新問題，我的頁面上有一個UIScrollView和一個定時器用來記錄當前考試模式下的剩餘時間，問題出現了：當我滑動滾動試圖時，定時器的方法便不在運行（即被UI主線程阻塞）。google一下找到瞭解決辦法：將定時器放在非主線程中執行將更新UI的操作放到主線程，這樣UI主線程和定時器就能互不干擾的相互工作了，以下是主要代碼：

          UILabel *     NSTimer *     @property (nonatomic, copy) NSString  * @property (nonatomic, copy) NSString  * @property (nonatomic, copy) NSString  *     hour =  minute =  second =  totalSeconds =  - (         - (      self =              _lblShow =         _lblShow.backgroundColor =         _lblShow.font = [UIFont systemFontOfSize:         _lblShow.textColor =         _lblShow.textAlignment =         _lblShow.numberOfLines =           - (       (self =         self.totalSeconds = minute *                   - (      _timer = [NSTimer scheduledTimerWithTimeInterval:   - (      self.hour = _totalSeconds/     self.minute = _totalSeconds%/     self.second = _totalSeconds%%      (_hour <=          _lblShow.text = [NSString stringWithFormat:     }         _lblShow.text = [NSString stringWithFormat:   - (      _hour =      (_hour <          self.strHour = [NSString stringWithFormat:     }         self.strHour = [NSString stringWithFormat:   - (      _minute =      (_minute <          self.strMinute = [NSString stringWithFormat:     }         self.strMinute = [NSString stringWithFormat:   - (      _second =      (_second <          self.strSecond = [NSString stringWithFormat:     }         self.strSecond = [NSString stringWithFormat:   - (      _totalSeconds =   - (       (_totalSeconds ==                 self.totalSeconds -=