Section content area is extended unexpectedly for a boundary item

Number:rdar://FB8977366 Date Originated:21/01/2021
Status:Open Resolved:
Product:UIKit Product Version:iOS 14.3
Classification:Incorrect/Unexpected Behavior Reproducible:yes
Related to UICollectionView with Compositional Layout.

When adding a NSCollectionLayoutBoundarySupplementaryItem with extendsBoundary=false, the boundary of the section is extended unexpectedly.

I’ve included a reproduction. When showing the supplementary item with extendsBoundary=false, I’d expect the item to be added without changing the size of the section. However as can be seen in the reproduction, the following section is pushed down with some whitespace when this supplementary item is added.


Please note: Reports posted here will not necessarily be seen by Apple. All problems should be submitted at before they are posted here. Please only post information for Radars that you have filed yourself, and please do not include Apple confidential information in your posts. Thank you!