iOS 15 ONLY crash at -collectionView:viewForSupplementaryElementOfKind:atIndexPath:

Question

Created Nov ’21

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THIS IS iOS 15 ONLY - THE SAME CODE WORKS FOR iOS 14.x USING XCODE 13.x, see below for details

When using background elements with UICollectionViewFlowLayout and UICollectionViewCompositionalLayout in iOS 15 the following happens on .reloadData(), .reconfigureItems(...), and .reloadItems(...) only (initial load is fine):

collectionView:viewForSupplementaryElementOfKind:atIndexPath: is called for background view
Background view is dequeued SUCCESSFULLY
viewForSupplementaryElementOfKind returns the view
App crashes post viewForSupplementaryElementOfKind (sometimes up to seconds later) saying viewForSupplementaryElementOfKind has returned null

I have verified:

viewForSupplementaryElementOfKind IS dequeueing a cell
The cell IS the correct element
The element is returning
viewForSupplementaryElementOfKind IS valid
viewForSupplementaryElementOfKind loads correctly when the collectionView first loads; this only occurs on refreshing

PLEASE, re-read the very top statement again before replying to ensure you are not replying "you/viewForSupplementaryElementOfKind is returning nil, check you are not returning nil". I will happily run additional test.

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Answer 1

Frameworks Engineer OP

Apple

Dec ’21

It would help if you could post your code of a) how you register the supplementary view and b) how you dequeue and configure it. Also the exact exception message would be helpful.

With the information provided here, my best guess is that you are registering one element kind but then return another element kind. I.e. the element kind passed to you in viewForSupplementaryOfKind: is not the same element kind that is set on the cell when you return it / the identifier of what you are dequeuing is associated with a different element kind during registration of that class.

This is an issue as it completely breaks reusability, so starting in iOS 15 this case is detected and asserted.

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