Supplementary view resets to estimated height during animated layout change

Originator:kellerbryan19
Number:rdar://FB9811483 Date Originated:2021-12-16
Status:Open Resolved:No
Product:iOS / UIKit Product Version:iOS 15 SDK
Classification:Bug Reproducible:
 
When using `UICollectionViewCompositionalLayout` with self-sizing headers (estimated height boundary supplementary view), the headers animate to their estimated height before snapping back to their actual height in some cases. The issue appears to happen when an item contained in the header’s section changes its width dimension. For example, changing an item’s width dimension from `.fractional(1)` to `.fractional(0.5)` will cause the section’s header to animate to an estimated height.

The animation is implemented by calling `invalidateLayout()` in a `performBatchUpdates` closure.

See the attached example project for the exact setup.

https://drive.google.com/file/d/12THxYgep4ef1LaC1K2jXn1Ytq6QkxKeU/view?usp=sharing

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