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 w

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.

Answer 2

I would do this:

Objective-C

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

and implement this protocol

- (void)scrollViewDidScroll:(UIScrollView *)scrollView

Swift

for view in self.pageViewController.view.subviews {
  if let scrollView = view as? UIScrollView {
    scrollView.delegate = self
  }
}

and implement this protocol

func scrollViewDidScroll(scrollView: UIScrollView)