Remove x,y from measureParentSize — fixes Fabric sticky header offset#2105
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thomasttvo wants to merge 3 commits intoShopify:mainfrom
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Remove x,y from measureParentSize — fixes Fabric sticky header offset#2105thomasttvo wants to merge 3 commits intoShopify:mainfrom
thomasttvo wants to merge 3 commits intoShopify:mainfrom
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measureParentSize uses a self-relative measureLayout call (view.measureLayout(view, cb)) to get the view's width and height. The x,y values from this call are always (0,0) on Paper and web since a view's position relative to itself is the origin. The downstream firstItemOffset calculation subtracted outerViewLayout.x/y which was always a no-op. Remove x,y from the return type (Layout -> Size), drop the dead subtractions in RecyclerView, and rename outerViewLayout to outerViewSize to reflect what it actually contains. Co-Authored-By: Claude Sonnet 4.5 (1M context) <noreply@anthropic.com>
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Tests verify that sticky headers don't activate prematurely when measureParentSize returns non-zero y values (as it does on Fabric when there's content above the FlashList). Covers three cases: no content above, 50px above, and 100px above. These tests fail on the old code (which subtracted outerViewLayout.y from firstItemOffset) and pass with the fix. Co-Authored-By: Claude Sonnet 4.5 (1M context) <noreply@anthropic.com>
Reduce type casts, improve naming, and simplify the describe/test structure for clarity. Co-Authored-By: Claude Sonnet 4.5 (1M context) <noreply@anthropic.com>
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Summary
measureParentSizeuses a self-relativemeasureLayoutcall (view.measureLayout(view, cb)) to get the outer container's width and height. The returned x,y from this call are always (0,0) on Paper and web — a view's position relative to itself is the origin.The downstream
firstItemOffsetcalculation inRecyclerViewsubtractedouterViewLayout.x/y, which was always a no-op (subtracting 0). This dead subtraction masked a Fabric compatibility issue: on Fabric, the self-relativemeasureLayoutcall returns the view's position in its parent instead of (0,0), corruptingfirstItemOffsetfor any FlashList with content above it.Proof that
view.measureLayout(view, cb)returns (0,0) on Paper: thomasttvo/rn-measure-layout-bug (RN 0.81.5,RCT_NEW_ARCH_ENABLED=0)Repro of downstream effect on sticky headers: thomasttvo/flashlist-sticky-header-repro
Related issues: #1942, #2017
Changes
measureParentSizenow returnsSize({width, height}) instead ofLayout({x, y, width, height})- outerViewLayout.x/ysubtractions fromfirstItemOffsetcalculationouterViewLayouttoouterViewSizeto reflect what it actually containsmeasureLayout.web.tsmeasureParentSizereturns non-zero y (simulating Fabric with content above the FlashList). Tests cover 0px, 50px, and 100px offsets — they fail on the old code and pass with this fix.