@@ -112,6 +112,11 @@ public final class ChatLayout: UICollectionViewLayout {
112112 return contentSize
113113 }
114114
115+ /// There is an issue in IOS 15.1 that proposed content offset is being ignored by the UICollectionView when user is scrolling.
116+ /// This flag enables a hack to compensate this offset later. You can disable it if necessary.
117+ /// Bug reported: https://feedbackassistant.apple.com/feedback/9727104
118+ public var enableIOS15_1Fix : Bool = true
119+
115120 // MARK: Internal Properties
116121
117122 var adjustedContentInset : UIEdgeInsets {
@@ -175,6 +180,12 @@ public final class ChatLayout: UICollectionViewLayout {
175180
176181 private let _flipsHorizontallyInOppositeLayoutDirection : Bool
177182
183+ // MARK: IOS 15.1 fix flags
184+
185+ private var needsIOS15_1IssueFix : Bool {
186+ return enableIOS15_1Fix && isIOS15_1orHigher && isUserInitiatedScrolling && !controller. isAnimatedBoundsChange
187+ }
188+
178189 // MARK: Constructors
179190
180191 /// Default constructor.
@@ -609,9 +620,16 @@ public final class ChatLayout: UICollectionViewLayout {
609620 let collectionView = collectionView {
610621 let minPossibleContentOffset = - collectionView. adjustedContentInset. top
611622 let newProposedContentOffset = CGPoint ( x: proposedContentOffset. x, y: max ( minPossibleContentOffset, min ( proposedContentOffset. y + controller. proposedCompensatingOffset, maxPossibleContentOffset. y) ) )
612- controller. proposedCompensatingOffset = 0
613623 invalidationActions. formUnion ( [ . shouldInvalidateOnBoundsChange] )
614- return newProposedContentOffset
624+ if needsIOS15_1IssueFix {
625+ // This fix affects performance as UICollectionView will request cells event though they wont be visible on the screen.
626+ // It also causes a small flickering as content offset is being fixed at `finalizeCollectionViewUpdates` instead.
627+ controller. batchUpdateCompensatingOffset += controller. proposedCompensatingOffset
628+ return super. targetContentOffset ( forProposedContentOffset: proposedContentOffset)
629+ } else {
630+ controller. proposedCompensatingOffset = 0
631+ return newProposedContentOffset
632+ }
615633 }
616634 return super. targetContentOffset ( forProposedContentOffset: proposedContentOffset)
617635 }
@@ -949,3 +967,12 @@ var isIOS13orHigher: Bool {
949967 return false
950968 }
951969}
970+
971+ @inline ( __always)
972+ var isIOS15_1orHigher : Bool {
973+ if #available( iOS 15 . 1 , * ) {
974+ return true
975+ } else {
976+ return false
977+ }
978+ }
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