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Fix jumpy scrolling due to incorrect target content offset calculation #137

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Merged
merged 1 commit into from
Jul 14, 2025
Merged

Fix jumpy scrolling due to incorrect target content offset calculation #137

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11 changes: 11 additions & 0 deletions MagazineLayout/LayoutCore/ModelState.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -105,6 +105,17 @@ final class ModelState {
return nil
}

func isItemHeightSettled(indexPath: IndexPath) -> Bool {
let item = sectionModels(for: .afterUpdates)[indexPath.section].itemModel(
atIndex: indexPath.item)
switch item.sizeMode.heightMode {
case .static:
return true
case .dynamicAndStretchToTallestItemInRow, .dynamic(_):
return item.preferredHeight != nil
}
}

func itemModelHeightModeDuringPreferredAttributesCheck(
at indexPath: IndexPath)
-> MagazineLayoutItemHeightMode?
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6 changes: 5 additions & 1 deletion MagazineLayout/Public/MagazineLayout.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -1294,7 +1294,11 @@ public final class MagazineLayout: UICollectionViewLayout {
}
visibleItemLocationFramePairs.sort { $0.elementLocation < $1.elementLocation }

let firstVisibleItemLocationFramePair = visibleItemLocationFramePairs.first
let firstVisibleItemLocationFramePair = visibleItemLocationFramePairs.first {
// When scrolling up, only calculate a a target content offset based on visible, already-sized
// cells. Otherwise, scrolling will be jumpy.
modelState.isItemHeightSettled(indexPath: $0.elementLocation.indexPath)
}
let lastVisibleItemLocationFramePair = visibleItemLocationFramePairs.last

guard
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