-(void) beginTimer
{
    __block int timeout = 3610; //倒计时时间
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_source_t _timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0,queue);
    dispatch_source_set_timer(_timer,dispatch_walltime(NULL, 0),1.0*NSEC_PER_SEC, 0); //每秒执行
    dispatch_source_set_event_handler(_timer, ^{
        if(timeout<=0){ //倒计时结束，关闭
            dispatch_source_cancel(_timer);
            dispatch_async(dispatch_get_main_queue(), ^{
                timerLabel.text = @"go 你可以去刮了";
                
            });
        }
        else
        {
            
            int hour = timeout / 60 / 60;
            int min = (timeout - (hour * 60 * 60)) / 60;
            int seconds = timeout - (hour * 60 * 60) - (min * 60);
            
            dispatch_async(dispatch_get_main_queue(), ^{
                timerLabel.text = [NSString stringWithFormat:@"%02ld:%02ld:%02ld",(long)hour,(long)min,(long)seconds];
            });
            timeout--;
            
        }  
    });  
    dispatch_resume(_timer);
}

显示

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