Hii, Im facing this Crash - iOS fatal: `ArrayIndex...

# compose-ios

[Sagar Khurana]

Hii, Im facing this Crash - iOS fatal: ArrayIndexOutOfBoundsException in LazyStaggeredGridMeasure during LookaheadPass with StaggeredGridCells.Adaptive inside AnimatedPane

50+ crashes for 41 users in the last 7 days

[Sagar Khurana]

We're hitting a fatal crash in production on iOS (Compose Multiplatform 1.10.1, Compose Foundation 1.10.1):

kotlin.ArrayIndexOutOfBoundsException at LazyStaggeredGridMeasure.kt:269

Setup:
- LazyVerticalStaggeredGrid(columns = StaggeredGridCells.Adaptive(150.dp))
- Hosted in ListDetailPaneScaffold -> AnimatedPane
- Crash commonly occurs on back navigation (Detail -> Home)

Top of stack:

ThrowArrayIndexOutOfBoundsException (RuntimeUtils.kt:41)
  LazyStaggeredGridMeasure.measure (LazyStaggeredGridMeasure.kt:269)
  rememberStaggeredGridMeasurePolicy (LazyStaggeredGridMeasure.kt:184)
  LazyLayout (Composer.kt:189)
  InnerNodeCoordinator.LookaheadDelegateImpl.measure (MeasurePolicy.kt:88)
  CupertinoOverscrollNode.measure (Measurable.kt:30)
  LayoutModifierNodeCoordinator.LookaheadDelegateForLayoutModifierNode.measure
  LookaheadPassDelegate.remeasure (OwnerSnapshotObserver.kt:138)
  LookaheadPassDelegate.measure (LookaheadPassDelegate.kt:404)
  BoxMeasurePolicy.measure (Measurable.kt:30)

No app code at throw site, entirely within Compose framework.


Questions:
1) Is this a known issue for LookaheadScope + LazyVerticalStaggeredGrid + Adaptive columns on iOS?
2) Is there an existing issue ID / planned fix?
3) Should staggered grid measure guard lane-count changes across lookahead/actual passes?

[Mark Murphy]

this issue comment seems to resemble your situation, though the poster declined to provide a reproducible sample

[Sagar Khurana]

Hey @Mark Murphy, thanks for pointing us to that issue comment. That's exactly our situation. We investigated the root cause and found it's a measurement race: Adaptive computes the column count per pass, and LookaheadScope (from AnimatedPane) runs two passes with different widths during animation. When those widths cross a column-count boundary, the lane arrays go out of sync → ArrayIndexOutOfBoundsException.

We applied the workaround from that thread, replacing Adaptive with Fixed(N) computed via BoxWithConstraints, so the lane count is determined once at composition time, not per measurement pass. Shipping it now and will keep an eye on crash reports post-release. We also added our findings to the issue tracker. Thanks again for the quick pointer!