iOS-GCD定时器

第一种网页中查的

 NSTimeInterval period = 1.0;

    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

    _defaultTimer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);

    dispatch_source_set_timer(_defaultTimer, dispatch_walltime(NULL, 0), period * NSEC_PER_SEC, 0);



    __block NSInteger duration = defaultDuration;

    dispatch_source_set_event_handler(_defaultTimer, ^{



        dispatch_async(dispatch_get_main_queue(), ^{

            if(duration==0)

            {

                dispatch_source_cancel(_defaultTimer);

                [self remove];

            }

            duration--;

        });

    });

    dispatch_source_set_cancel_handler(_defaultTimer, ^{

        dispatch_release(_defaultTimer);

    });

    dispatch_resume(_defaultTimer);

第二种项目中的

-(void)getStartTime{
     __block int timeout=30; //倒计时时间
    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);
    dispatch_source_set_event_handler(timer, ^{
        if (timeout<=0) {
            dispatch_source_cancel(timer);
            dispatch_async(dispatch_get_main_queue(), ^{
                self.VerificationLbl.backgroundColor = main_Color;
                self.VerificationLbl.text = @"获取验证码";
                self.VerificationLbl.textColor = [UIColor whiteColor];
                self.VerificationLbl.userInteractionEnabled = YES;
            });
        }else{
            if (backDate && frontDate) {
                NSTimeInterval backDates = [backDate timeIntervalSinceReferenceDate];
                NSTimeInterval frontDates = [frontDate timeIntervalSinceReferenceDate];
                int interval = frontDates - backDates;
                timeout=timeout-interval;
                backDate=nil;
                frontDate=nil;
            }
            dispatch_async(dispatch_get_main_queue(), ^{
                //NSLog(@"每秒执行一次");
                DebugLog(@"倒计时---%d",timeout);
                self.VerificationLbl.backgroundColor = [UIColor grayColor];
                self.VerificationLbl.text = [NSString stringWithFormat:@"%ds",timeout];
                self.VerificationLbl.userInteractionEnabled = NO;
            });
            timeout--;
        }
    });
    dispatch_resume(timer);
}