GCD定時器驗證碼倒計時，gcd定時器驗證碼

GCD定時器驗證碼倒計時，gcd定時器驗證碼

- (IBAction)butClick:(UIButton *)but {    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);    __block NSInteger time = count;    dispatch_source_set_event_handler(_timer, ^{        if(time<=0){            dispatch_source_cancel(_timer);            dispatch_async(dispatch_get_main_queue(), ^{                [but setTitle:@"重新擷取" forState:UIControlStateNormal];                but.userInteractionEnabled = YES;                but.alpha = 1.0;                but.backgroundColor = [UIColor whiteColor];            });        } else {            NSString *strTime = [NSString stringWithFormat:@"%lds", (long)time];            dispatch_async(dispatch_get_main_queue(), ^{                [but setTitle:strTime forState:UIControlStateNormal];                but.userInteractionEnabled = NO;                but.backgroundColor = [UIColor lightTextColor];            });            time--;        }    });    dispatch_resume(_timer);}