/** 獲取一個全局的線程來運行計時器*/
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
/** 創(chuàng)建一個計時器*/
dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
/** 設置計時器, 這里是每10毫秒執(zhí)行一次*/
dispatch_source_set_timer(timer, dispatch_walltime(nil, 0), 10*NSEC_PER_MSEC, 0);
/** 設置計時器的里操作事件*/
dispatch_source_set_event_handler(timer, ^{
 //do you want....
});

dispatch_resume(timer);

/** 掛起的時候注意，多次暫停的操作會導致線程鎖的現(xiàn)象，即多少次暫停，
*  對應多少次的繼續(xù)操作，即dispatch_suspend和dispatch_resume
*  是成對出現(xiàn)的，計時器才會繼續(xù)工作。
*/
dispatch_suspend(timer);

dispatch_source_cancel(timer);

/** app進入后臺*/
- (void)appDidEnterBackground{
  [self suspend];
  NSDate *date = [[NSDate alloc] init];
  NSDateFormatter *format = [[NSDateFormatter alloc] init];
  format.dateFormat = @"yyyy-MM-dd HH:mm:ss:SSS";
  self.appDidEnterBackgroundTime = [date timeIntervalSince1970];
}

/** app進入前臺*/
- (void)appDidEnterForeground{
  NSDate *date = [[NSDate alloc] init];
  NSDateFormatter *format = [[NSDateFormatter alloc] init];
  format.dateFormat = @"yyyy-MM-dd HH:mm:ss";
  self.appDidEnterForegroundTime = [date timeIntervalSince1970];
  [self reCalculateMinder];
}

/** 不失精度加減乘除計算結(jié)果*/

- (NSDecimalNumber *)value: (NSTimeInterval)value 
        byOpration: (OMDecimalOprationType)byOpration    
         percision: (NSInteger)percision 
        withValue: (NSTimeInterval)withValue{

  NSDecimalNumber *number = [self numberValueWithString: value];
  NSDecimalNumber *withNumber = [self numberValueWithString: withValue]; 
  NSDecimalNumberHandler *handler = [NSDecimalNumberHandler decimalNumberHandlerWithRoundingMode: NSRoundPlain scale: percision raiseOnExactness: NO raiseOnOverflow: NO raiseOnUnderflow: NO raiseOnDivideByZero: YES];

switch (byOpration) {
  case OMDecimalOprationTypeAdd:
   return [number decimalNumberByAdding: withNumber withBehavior:handler];
   break;
  case OMDecimalOprationTypeSubtract:
   return [number decimalNumberBySubtracting: withNumber withBehavior: handler];
   break;
  case OMDecimalOprationTypeDivide:
   return [number decimalNumberByDividingBy: withNumber withBehavior: handler];
   break;
 case OMDecimalOprationTypeMultiple:
   return [number decimalNumberByMultiplyingBy: withNumber withBehavior: handler];
   break;
 default:
   break;
   return nil;
}

@property (nonatomic, strong) OMTimer *timer;

self.timer = [[OMTimer alloc] init];
self.timer.timerInterval = 30;
self.timer.precision = 100;
self.timer.isAscend = NO;
self.timer.progressBlock = ^(OMTime *progress) {
   NSLog(@"%@:%@:%@:%@", progress.hour, progress.minute, progress.second, progress.millisecond;
};self.timer.completion = ^{
  NSLog(@"complete done!");
};