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Fix iPhone Duo having stale width in some cases #170

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Merged
bryankeller merged 2 commits into from
Oct 13, 2026
Merged

Fix iPhone Duo having stale width in some cases #170

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2c6f5a4
Fix iPhone Duo having stale width in some cases
Oct 12, 2026
c40d97c
Review feedback - consolidate width measurement and invalidation in p…
Oct 13, 2026
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37 changes: 17 additions & 20 deletions MagazineLayout/Public/MagazineLayout.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -82,10 +82,24 @@ public final class MagazineLayout: UICollectionViewLayout {
_currentCollectionView = collectionView
_delegateMagazineLayout = currentCollectionView.delegate as? UICollectionViewDelegateMagazineLayout

// Save the previous collection view width and horizontal insets if necessary
if prepareActions.contains(.cachePreviousHorizontalMetrics) {

@ephraimkunz ephraimkunz Oct 13, 2026

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No need for this action any more, since we can just check it below.

// The width and horizontal insets can change after `invalidateLayout(with:)` runs without it being
// called again, so it can't reliably detect these changes. UIKit skips
// `shouldInvalidateLayout(forBoundsChange:)` while the layout is already invalidated, assuming the
// pending `prepare()` will read the new bounds. On iPhone Duo rotating while closed, the size-class
// batch update finishes before the collection view is resized, so the new width arrives after
// `invalidateLayout(with:)` has already run. Comparing here sees the final values.
let isSameWidth = currentCollectionView.bounds.width.isEqual(
to: cachedCollectionViewWidth ?? -.greatestFiniteMagnitude,
screenScale: scale)
let horizontalContentInset = contentInset.left + contentInset.right
let isSameHorizontalContentInset = horizontalContentInset.isEqual(
to: cachedHorizontalContentInset ?? -.greatestFiniteMagnitude,
screenScale: scale)

if !isSameWidth || !isSameHorizontalContentInset {
cachedCollectionViewWidth = currentCollectionView.bounds.width
cachedHorizontalContentInset = contentInset.left + contentInset.right
cachedHorizontalContentInset = horizontalContentInset
prepareActions.formUnion(.updateLayoutMetrics)
}

if
Expand Down Expand Up @@ -875,22 +889,6 @@ public final class MagazineLayout: UICollectionViewLayout {
prepareActions.formUnion(.recreateSectionModels)
}

// Manually checking for a different width or different horizontal insets is necessary because
// these values can change without a `contentSizeAdjustment` occurring.
let isSameWidth = collectionView?.bounds.size.width.isEqual(
to: cachedCollectionViewWidth ?? -.greatestFiniteMagnitude,
screenScale: scale)
?? false
let horizontalContentInset = (collectionView?.adjustedContentInset.left ?? 0) +
(collectionView?.adjustedContentInset.right ?? 0)
let isSameHorizontalContentInset = horizontalContentInset.isEqual(
to: cachedHorizontalContentInset ?? -.greatestFiniteMagnitude,
screenScale: scale)
if !isSameWidth || !isSameHorizontalContentInset {
prepareActions.formUnion(.cachePreviousHorizontalMetrics)
prepareActions.formUnion(.updateLayoutMetrics)
}

if context.invalidateLayoutMetrics && shouldInvalidateLayoutMetrics {
prepareActions.formUnion(.updateLayoutMetrics)
}
Expand Down Expand Up @@ -969,7 +967,6 @@ public final class MagazineLayout: UICollectionViewLayout {

static let recreateSectionModels = PrepareActions(rawValue: 1 << 0)
static let updateLayoutMetrics = PrepareActions(rawValue: 1 << 1)
static let cachePreviousHorizontalMetrics = PrepareActions(rawValue: 1 << 2)
}
private var prepareActions: PrepareActions = []

Expand Down
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