iOS: Constraint animation

I wanted to animate a floating bar.

- (void)viewDidLoad
{
[super viewDidLoad];

self.floatingBar.hidden = YES;

    for (NSLayoutConstraint* contraint in self.view.constraints) {

        if ([contraint.identifier isEqualToString:@"top"]) {

            contraint.constant = -65 - self.floatingBar.frame.size.height;

            break;

        }

    }

...

}

#pragma mark - UIScrollViewDelegate

- (void)scrollViewDidScroll:(UIScrollView *)scrollView

{

    CGPoint offset = scrollView.contentOffset;

    

    if (offset.y < 400*) {

        if (!self.floatingBar.hidden) {

            self.floatingBar.hidden = YES;

            for (NSLayoutConstraint* contraint in self.view.constraints) {

                if ([contraint.identifier isEqualToString:@"top"])** {

                    contraint.constant = -65*** - self.floatingBar.frame.size.height;

                    break;

                }

            }

        }

        

    } else if (offset.y > 400) {

        if (self.floatingBar.hidden) {

            self.floatingBar.hidden = NO;

            

            [self.view layoutIfNeeded];

            

            [UIView animateWithDuration:1 delay:0 options:UIViewAnimationOptionCurveEaseOut animations:^{

                

                for (NSLayoutConstraint* contraint in self.view.constraints) {

                    if ([contraint.identifier isEqualToString:@"top"]) {

                        contraint.constant = -65;

                        break;

                    }

                }

                

                [self.view layoutIfNeeded];

                

            } completion:^(BOOL finished) {

                

            }];

        }

    }

}

* 400 was my threshhold

** Name of my constraint (identifier I used in interface builder)

*** I wanted my bar to be at the top of the window (under status bar and navigation bar)