fix(ios): skip programmatic selectRow while user is scrolling (Fabric crash)#674
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raid5 wants to merge 1 commit into
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fix(ios): skip programmatic selectRow while user is scrolling (Fabric crash)#674raid5 wants to merge 1 commit into
raid5 wants to merge 1 commit into
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On the New Architecture (Fabric), a controlled Picker can crash with EXC_BAD_ACCESS during a fast fling. Every committed value flows through -setSelectedIndex:, which calls -selectRow:animated:. Mid-gesture, lagging React state echoes back a stale index that re-drives the live wheel, re-entering UIPickerView's suspended update cycle during UIKit hit-testing. Add an -isUserScrolling helper that inspects the picker's backing UIScrollView(s) (isTracking/isDragging/isDecelerating) and bail out of -setSelectedIndex: while the user is actively manipulating the wheel. -didSelectRow: already keeps the internal index accurate, so idle programmatic resets continue to work.
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Summary
Fixes an intermittent native crash on iOS when a controlled
Pickeris scrolled quickly under the New Architecture (Fabric). The fix skips the programmatic re-selection of a row while the user is physically dragging/flinging the wheel.Problem
With a controlled picker (
selectedValuedriven by React state), fast scrolling can crash the app withEXC_BAD_ACCESSinside UIKit's_endSuspendingUpdates. It reproduces reliably on Fabric builds and does not occur on the old architecture, because the two architectures batch prop updates differently.Repro:
PickerwhoseselectedValueis a controlled React state value updated fromonValueChange.Root cause
Every committed
selectedValueflows into-[RNCPicker setSelectedIndex:], which calls-selectRow:animated:. During a fling, React state lags the live native wheel and echoes back a now-stale index. That stale value re-drivesselectRow:in the middle of the active gesture, re-enteringUIPickerView's suspended update cycle while UIKit is hit-testing — hence the crash. On the old architecture the update batching happened differently, so only New Architecture builds are affected.Fix
-isUserScrollinghelper that walks the picker's internal subview hierarchy and returns whether any backingUIScrollViewis currentlyisTracking,isDragging, orisDecelerating.-setSelectedIndex:that skips the programmatic re-drive while the user is actively manipulating the wheel.-didSelectRow:already keeps_selectedIndexin sync with the user's gesture, so no selection state is lost; programmatic resets performed while the wheel is idle continue to behave exactly as before. The change is confined toios/RNCPicker.mmand does not alter the JS API.Testing
This change has been running in a shipping iOS app built with the New Architecture, where it eliminated a recurring
EXC_BAD_ACCESSinside UIKit's_endSuspendingUpdatesduring fast scrolling of a controlled picker.selectedValuecontinue to move the wheel as expected on both the old and New Architecture.ios/RNCPicker.mmand does not alter the JS API, so the existing JS test suite is unaffected; the repo has no Objective-C unit-test harness to extend, so no automated test was added.This fix was prepared with AI assistance and reviewed by a human before submission.