iOS中GCD定时器(dispatch_source_t)

在日常一些项目中，常常用到定时器（一些活动，营销等等），在这里可以设置一下定时器：

.h文件：

@interface ViewController ()
@property (nonatomic, strong) dispatch_source_t           timer; // 倒计时
@end

.m文件：

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

  // 计算结束时间 - 现在时间
    NSInteger timeInterval = (market_end_time - market_now_time) / 1000;
    [self secondsCountDown:timeInterval]; // 单位：秒
}

#pragma mark 25.倒计时 （天 时 分 秒）
- (void)secondsCountDown:(NSInteger)seconds {

    __weak __typeof(self) weakSelf = self;

    if (_timer == nil) {
        __block NSInteger timeout = seconds; // 倒计时时间

        if (timeout!=0) {
            dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
            _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){ //  当倒计时结束时做需要的操作: 关闭 活动到期不能提交
                    dispatch_source_cancel(weakSelf.timer);
                    weakSelf.timer = nil;
                    dispatch_async(dispatch_get_main_queue(), ^{
                        weakSelf.limitedTimeHotView.timeLabel.text = @"当前活动已结束";
                    });
                } else { // 倒计时重新计算 时/分/秒
                    NSInteger days = (int)(timeout/(3600*24));
                    NSInteger hours = (int)((timeout-days*24*3600)/3600);
                    NSInteger minute = (int)(timeout-days*24*3600-hours*3600)/60;
                    NSInteger second = timeout - days*24*3600 - hours*3600 - minute*60;
                    NSString *strTime = [NSString stringWithFormat:@"%ld时%ld分%ld", hours, minute, second];
                    dispatch_async(dispatch_get_main_queue(), ^{
                        if (days == 0) {
                            weakSelf.limitedTimeHotView.timeLabel.text = strTime;
                        } else {
                            weakSelf.limitedTimeHotView.timeLabel.text = [NSString stringWithFormat:@"%ld天%ld时%ld分%ld", days, hours, minute, second];
                        }

                    });
                    timeout--; // 递减 倒计时-1(总时间以秒来计算)
                }
            });
            dispatch_resume(_timer);
        }
    }

}
@end