objective c - Tell When a UIPageViewController is Scrolling (for Parallax Scrolling of an Image)

Question

I am trying to make an effect similar to that found in the new Yahoo weather app. Basically, each page in the UIPageViewController has a background image, and when scrolling through the page view, the Image's location only scrolls about half the speed. How would I do that? I thought I could use some sort of Delegate Method in the UIPageViewController to get the current offset and then update the images like that. The only problem is that I cannot find anyway to tell if the UIPageViewController is being scrolled! Is there a method for that? Thanks!

Answer 1

for (UIView *view in self.pageViewController.view.subviews) {
    if ([view isKindOfClass:[UIScrollView class]]) {
         [(UIScrollView *)view setDelegate:self];
    }
} 

this gives you access to all standard scroll view API methods. And this is not using private Apple API's.

I added traversing through subviews, to 100% find the UIPageViewController's inner scroll view WARNING: Be careful with scrollview.contentOffset. It resets as the controller scrolls to new pages

If you need persision scrollview offset tracking and stuff like that, it would be better to use a UICollectionViewController with cells sized as the collection view itself and paging enabled.