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Fix ListWheelScrollView null check error when it reads itemIndex before content dimensions are set - #194859
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This pull request modifies ListWheelScrollView to handle cases where the viewport builds children before content dimensions are applied by returning a rounded index when hasContentDimensions is false. It also adds regression tests for these scenarios. Feedback suggests clamping the calculated index to zero when content dimensions are missing to prevent negative index errors, and simplifying the test code by removing a redundant Uint8List.fromList wrapper around kTransparentImage.
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Thanks for the fix and the thorough regression tests! This PR prevents a null-check error in _FixedExtentScrollPosition.itemIndex when itemIndex is queried during the first layout before content dimensions have been applied.
Note: The Google testing check is currently still in progress.
— renzo-olivares-agent is an AI reviewer; a human maintainer makes the final call (see this account's profile for who to contact).
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autosubmit label was removed for flutter/flutter/194859, because The base commit of the PR is older than 7 days and can not be merged. Please merge the latest changes from the main into this branch and resubmit the PR. |
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victorsanni
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Hi, is this ready for re-review? Please remember to request a review if it is, so it gets back into the review queue. |
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LGTM with comments.
Also can you update the PR description with the latest changes?
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Roll Flutter from 3623d2d34543 to 09175cdeac89 (61 revisions) flutter/flutter@3623d2d...09175cd 2026-11-06 [email protected] Roll Skia from ae35b7b2221f to 793b8ac73d4b (3 revisions) (flutter/flutter#196091) 2026-11-06 [email protected] [web] Rasterize scenes at the size passed to `FlutterView.render` (flutter/flutter#196052) 2026-11-06 [email protected] Roll Skia from 4aa043a81e0c to ae35b7b2221f (1 revision) (flutter/flutter#196086) 2026-11-06 [email protected] Roll Fuchsia Linux SDK from Fqe3UlLwAohsPbsCS... to KIc0XZbhLmvDpTluZ... (flutter/flutter#196085) 2026-11-06 [email protected] Allow a zero scale change in InteractiveViewer (flutter/flutter#194949) 2026-11-06 [email protected] Roll Skia from dd5c2553a856 to 4aa043a81e0c (2 revisions) (flutter/flutter#196079) 2026-11-06 [email protected] [web] Keep ImageFilter.blur bounds in equality and description (flutter/flutter#196013) 2026-11-06 [email protected] iOS: Remove unused PlatformViewIOS setup from FlutterPlatformViewsTest (flutter/flutter#196033) 2026-11-06 [email protected] Serialize LoggerTests that mutate the shared Logger (flutter/flutter#196028) 2026-11-06 [email protected] Use reverseDuration for the AnimatedCrossFade size animation (flutter/flutter#194860) 2026-11-05 [email protected] Roll Skia from a5aacd103e68 to dd5c2553a856 (8 revisions) (flutter/flutter#196073) 2026-11-05 [email protected] Fix ListWheelScrollView null check error when it reads itemIndex before content dimensions are set (flutter/flutter#194859) 2026-11-05 [email protected] Allow zero cross axis extent in SliverGridDelegateWithMaxCrossAxisExtent (flutter/flutter#194858) 2026-11-05 [email protected] Revert: Allow color delta tolerance in in-memory fuzzy image comparator (flutter/flutter#196067) 2026-11-05 [email protected] Revert: Mitigate snapshot race in 3D transform test by reducing loop density (flutter/flutter#196066) 2026-11-05 [email protected] Delegate createStream in ResizeImage and ScrollAwareImageProvider (flutter/flutter#194756) 2026-11-05 [email protected] [iOS] Introduce FlutterShell and move thread host and profiler (flutter/flutter#195388) 2026-11-05 [email protected] [web] Support FragmentShader.getImageSampler on CanvasKit and Skwasm (flutter/flutter#195854) 2026-11-05 [email protected] Deprecates setFloat API (flutter/flutter#195505) 2026-11-05 [email protected] [flutter_tools] Remove public GlobalToolContext and globals from runner (flutter/flutter#195561) 2026-11-05 [email protected] Defer TLHC PlatformViewWrapper frame post and avoid initial 1x1 buffer resize (flutter/flutter#195861) 2026-11-05 [email protected] Roll Skia from b5abed66da86 to a5aacd103e68 (17 revisions) (flutter/flutter#196054) 2026-11-05 [email protected] Made `FlutterWindowControllerSizeTest.SizedToContentNotResizable` more robust (flutter/flutter#195845) 2026-11-05 [email protected] Update docs for contributor ladder (flutter/flutter#196011) 2026-11-05 [email protected] [Impeller] Use the transfer stage for the Vulkan readback barrier (flutter/flutter#194991) 2026-11-05 [email protected] Remove Mac mac_unopt builder (flutter/flutter#196027) 2026-11-05 [email protected] Updated Instructions for Determining Gradle Version for `gradle_dists` in CIPD (flutter/flutter#193310) 2026-11-05 [email protected] Move ios_app_with_extensions_test into the tool integration shard (flutter/flutter#195609) 2026-11-05 [email protected] [web] Respect Uint8List view bounds when detecting animated WebP/GIF (flutter/flutter#196010) 2026-11-05 [email protected] Add platform_views_layout to build_tests so iOS/Android build breaks are caught in presubmit (flutter/flutter#192985) 2026-11-05 [email protected] [flutter_tools] Detect macOS TCC permission crashes and provide diagnostic guidance (flutter/flutter#192432) 2026-11-05 [email protected] Roll Packages from 670b30e to 0478162 (15 revisions) (flutter/flutter#196047) 2026-11-05 [email protected] [web] Support Skwasm rendering without bitmap capture (flutter/flutter#195103) 2026-11-05 [email protected] [flutter_tools] Reland fix for local CanvasKit asset paths on Windows (flutter/flutter#195770) 2026-11-05 [email protected] Roll Skia from f96be51af95d to b5abed66da86 (14 revisions) (flutter/flutter#196017) 2026-11-05 [email protected] Split chrome web engine test drone (flutter/flutter#195873) 2026-11-05 [email protected] Roll Dart SDK from c9153304136a to 6623b84628f3 (1 revision) (flutter/flutter#196026) 2026-11-05 [email protected] Roll ICU from 4fe960221710 to a0ea93436c52 (6 revisions) (flutter/flutter#196025) 2026-11-05 [email protected] Add more guidance in README and AGENTS for contributing to flutter_tools (flutter/flutter#195998) 2026-11-05 [email protected] Roll Fuchsia Linux SDK from p0HDXLISPIElJfSz7... to Fqe3UlLwAohsPbsCS... (flutter/flutter#196019) 2026-11-05 [email protected] Roll Dart SDK from e362a23e9738 to c9153304136a (18 revisions) (flutter/flutter#196014) 2026-11-05 [email protected] [Impeller] Fix dilation input bounds when clipping saveLayers (flutter/flutter#195652) 2026-11-05 [email protected] Add `variantOf` to the M3E migration checklist (flutter/flutter#195099) 2026-11-05 [email protected] [flutter_tools] Eliminate globals from remaining subsystem files (flutter/flutter#195555) 2026-11-05 [email protected] Fix gap flipping when dragging variable height reorderable items (flutter/flutter#194478) 2026-11-05 [email protected] [A11y] Send un-merged SemanticsNodes in the same update that first references them (flutter/flutter#195829) ...
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ListWheelScrollViewthrowsNull check operator used on a null valueduring its first layout when a child reads the selected item. A common case is anImagechild. The images then show only after the user scrolls the wheel.The viewport builds its children before it calls
applyContentDimensions. During this time, anImagechild resolves its image. This callsScrollPosition.recommendDeferredLoading, which calls_FixedExtentScrollPosition.copyWith, which readsitemIndex.itemIndexreadsminScrollExtentandmaxScrollExtent, and these are not set yet. Code that readsFixedExtentScrollController.selectedItemduring layout has the same problem.This PR changes
_FixedExtentScrollPosition.itemIndex. When the position has no content dimensions, it returns(pixels / itemExtent).round(). This is the same calculation without the clamp to the scroll extents. When the position has content dimensions, the behavior does not change.FixedExtentMetrics.copyWithalready uses the samehasContentDimensionscheck.Fixes #125997
Tests
This PR adds regression tests to
packages/flutter/test/widgets/list_wheel_scroll_view_test.dart:ListWheelScrollView can resolve images during its first layout: aListWheelChildBuilderDelegatewith a nullchildCountandImagechildren. The test checks that there is no exception and that the images resolve (imageCache.liveImageCountis greater than 0). It clears the image cache when it ends.Looping ListWheelScrollView can read selectedItem during its first layout (initialItem: $initialItem): aListWheelChildLoopingListDelegatewithinitialItem7 and -3. Each child readsselectedItemduring layout. The test checks that all values are equal toinitialItem.Before this change, the three tests fail:
After this change,
flutter test test/widgets/list_wheel_scroll_view_test.dartpasses:Pre-launch Checklist
///). No doc change is necessary.If you need help, consider asking for advice on the #hackers-new channel on Discord.