Scroll-Based Animation in iOS

gistfile1.m

- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    CGFloat scrollOffset = scrollView.contentOffset.y;
    
    // Shift dismiss button up on scroll when user is at the top of the scrollview
    if (scrollOffset < -[self tableViewOffsetTop]) {
        self.dismissButton.transform = CGAffineTransformMakeTranslation(0, scrollOffset + [self tableViewOffsetTop]);
    }
    
    // Dismiss after user scrolls down far enough
    
    CGFloat dismissThreshold = -([self tableViewOffsetTop] + 80);

    if (scrollOffset < dismissThreshold) {
        self.dismissButton.hidden = YES;
        [self dismissHotlines];
    }
}

- (CGFloat)tableViewOffsetTop
{
    return [UIScreen screenHeight] / 4.0f;
}