Open Radar

 
Summary:
UIScrollView has a nice SPI that lets other objects hook into didScroll to be able to update things based on a scroll event. This is a very helpful API and as of iOS 11 it looks like this SPI has even be more improved and it looks like this now is a nice block based registration pattern.

Making this publicly available would be great for apps and frameworks alike.

Steps to Reproduce:
 

Expected Results:
 

Actual Results:
 

Version:
11b4

Notes:
While this can be implemented on client side pretty easily with a subclass to UIScrollView the benefit of having this publicly available on UIScrollView would be that all subclasses inherit this automatically. So on client side you wouldn’t need to build a subclass for UIScrollView, UICollectionView and other scroll view derived classes just to achieve this behavior. Furthermore when developing a framework, you might not know what you are dealing with, so e.g. looking up the view hierarchy for a scroll view and hooking into this currently is not possible in this cases simply because the component in question might not own the view in question.

A very great use case for this is also what UICollectionView does with its private `shouldDeriveVisibleBoundsFromContainingScrollView` logic. Being able to implement something like this on your own views would be very helpful.