fix(layout): prevent item overlap during fast scroll with dynamic heights#2196
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fix(layout): prevent item overlap during fast scroll with dynamic heights#2196github-actions[bot] wants to merge 1 commit intomainfrom
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…ghts When items have dynamic heights and the average height estimate grows, the partial recomputation of layout positions creates a boundary where items in the recomputed range shift forward while items beyond it keep their old (lower) positions. The previous guard only checked the very last item's position against the recomputed range boundary, which missed cases where the immediately-next item had a stale position going backwards. This broke the monotonic ordering that binary search relies on, causing items to overlap and jump during fast scrolling. Fix the guard to check the item immediately after the recomputed range instead of the last item, detecting position discontinuities at the boundary and triggering a full recomputation when needed. Fixes #2175
This was referenced Mar 23, 2026
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Description
When FlashList items have dynamic heights and early items are measured with heights significantly different from the initial estimate, the layout recomputation only covers a limited range of items. The guard condition that decides whether to extend the recomputation checked only the very last item's position against the boundary, missing cases where items immediately after the recomputed range had stale positions going backwards. This broke the monotonic position ordering that the binary search relies on, causing items to overlap, jump, and collapse during fast scrolling.
The fix changes the guard to check the item immediately after the recomputed range instead of the last item, correctly detecting position discontinuities at the boundary and triggering full recomputation when needed.
Fixes #2175
Reviewers' hat-rack 🎩
Focus on the guard condition change in
_recomputeLayoutsinLayoutManager.ts. The key question is whether checkingnextPos < endPos(position of item at endIndex+1 vs position of item at endIndex) is the right heuristic for all layout types (linear, grid, masonry). For grid layouts, items in the same row share the same y, sonextPos < endPosshould only trigger across row boundaries when positions truly go backwards.Test plan
yarn test)yarn type-check)yarn lint)