秒杀倒计时之dispatch

- (void)timerRun
{
    __block int timeout=60; //倒计时时间
    __block NSDate* startDate = [NSDate date];
    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(), ^{
                
            });
        }else{
            timeout = 60 - ([[NSDate date] timeIntervalSince1970] - [startDate timeIntervalSince1970]);
//            NSString *strTime = [NSString stringWithFormat:@"倒计时%.0d秒",timeout];
            dispatch_async(dispatch_get_main_queue(), ^{
                //设置界面的按钮显示 根据自己需求设置
                if (timeout >= 0) {
//                    [_getVerifiCodeBtn setTitle:strTime forState:UIControlStateNormal];
                }
            });
        }
    });
    dispatch_resume(_timer);
}