Framework: Improve DropdownButton selectedItemBuilder assertion#183732
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This pull request improves the developer experience by adding a clear assertion to the DropdownButton widget. When selectedItemBuilder returns a list with a length different from the items list, a descriptive error is now thrown during the build phase, preventing cryptic runtime errors. The change includes corresponding documentation updates and a new test case to validate the assertion. My review includes a suggestion to improve the readability of the new test case.
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| final List<DropdownMenuItem<String>> items = <String>['a', 'b'] | ||
| .map<DropdownMenuItem<String>>( | ||
| (String value) => DropdownMenuItem<String>(value: value, child: Text(value)), | ||
| ) | ||
| .toList(); |
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For creating a short, fixed list of items, initializing the list directly is more readable and performant (by using const) than using .map().toList(). This aligns with the style guide's principle to optimize for readability.
final List<DropdownMenuItem<String>> items = <DropdownMenuItem<String>>[
const DropdownMenuItem(value: 'a', child: const Text('a')),
const DropdownMenuItem(value: 'b', child: const Text('b')),
];References
- Code should be optimized for readability, as it is read more often than it is written. Using a list literal for a small, fixed collection is clearer than using
.map().toList(). (link)
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LGTM with a small nit in the test. Thank you!
Co-authored-by: Kate Lovett <katelovett@google.com>
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Whoops, forgot approval is dismissed after further changes. 😅
LGTM again!
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flutter/flutter@d117642...dd64978 2026-03-18 engine-flutter-autoroll@skia.org Roll Skia from 2fb5fa71eb12 to f0a13e5efbad (2 revisions) (flutter/flutter#183830) 2026-03-18 engine-flutter-autoroll@skia.org Roll Skia from ae3d36cb9e29 to 2fb5fa71eb12 (3 revisions) (flutter/flutter#183823) 2026-03-18 94012149+richardexfo@users.noreply.github.com Linux reuse sibling (flutter/flutter#183653) 2026-03-18 engine-flutter-autoroll@skia.org Roll Skia from 84a180a1fa80 to ae3d36cb9e29 (4 revisions) (flutter/flutter#183812) 2026-03-18 1961493+harryterkelsen@users.noreply.github.com fix(web): handle asynchronously disposed platform views (flutter/flutter#183666) 2026-03-17 87018443+mayanksharma9@users.noreply.github.com (Test cross-imports) Remove legacy Material import from sliver_constraints_test (flutter/flutter#183351) 2026-03-17 74057391+jhonathanqz@users.noreply.github.com Fix Android Studio pluginsPath when version is unknown (do not use 0.0) (flutter/flutter#182681) 2026-03-17 50643541+Mairramer@users.noreply.github.com Fixes animation glitch into bottom sheet (flutter/flutter#183303) 2026-03-17 ahmedsameha1@gmail.com Handle#6537 second grouped test (flutter/flutter#182529) 2026-03-17 ahmedsameha1@gmail.com Add a Clarification for the docs of suggestionsBuilder of SearchAnchor (flutter/flutter#183106) 2026-03-17 nate.w5687@gmail.com Remove obsolete null checks from style guide (flutter/flutter#181703) 2026-03-17 jason-simmons@users.noreply.github.com [Impeller] Do not delete the GL object in a HandleGLES if the handle has a cleanup callback (flutter/flutter#183561) 2026-03-17 jason-simmons@users.noreply.github.com Encode source file patches as UTF-8 in the code formatter script (flutter/flutter#183761) 2026-03-17 82673815+gktirkha@users.noreply.github.com Fix widget inspector control layout and add safe area regression test (flutter/flutter#180789) 2026-03-17 43054281+camsim99@users.noreply.github.com Reland "[Android] Add mechanism for setting Android engine flags via Android manifest (take 2)" (flutter/flutter#182522) 2026-03-17 1961493+harryterkelsen@users.noreply.github.com fix(web): fix crash in Skwasm when transferring non-transferable texture sources (flutter/flutter#183799) 2026-03-17 engine-flutter-autoroll@skia.org Roll Skia from dba893a44d7a to 84a180a1fa80 (7 revisions) (flutter/flutter#183803) 2026-03-17 brunocorona.alcantar@gmail.com Framework: Improve DropdownButton selectedItemBuilder assertion (flutter/flutter#183732) 2026-03-17 brunocorona.alcantar@gmail.com Add mainAxisAlignment to NavigationRail (flutter/flutter#183514) 2026-03-17 34871572+gmackall@users.noreply.github.com Update android triage process to not look at unassigned p1s every week (flutter/flutter#183805) 2026-03-17 30870216+gaaclarke@users.noreply.github.com Adds macos impeller new gallery transition perf test. (flutter/flutter#183802) 2026-03-17 1961493+harryterkelsen@users.noreply.github.com fix(web_ui): move prepareToDraw after raster to improve concurrency and stability (flutter/flutter#183791) 2026-03-17 rmacnak@google.com [build] Generate debug info for assembly. (flutter/flutter#183425) 2026-03-17 mdebbar@google.com [web] Fix occasional failure to find Chrome tab (flutter/flutter#183737) If this roll has caused a breakage, revert this CL and stop the roller using the controls here: https://autoroll.skia.org/r/flutter-packages Please CC boetger@google.com,stuartmorgan@google.com on the revert to ensure that a human is aware of the problem. To file a bug in Packages: https://github.com/flutter/flutter/issues/new/choose To report a problem with the AutoRoller itself, please file a bug: https://issues.skia.org/issues/new?component=1389291&template=1850622 Documentation for the AutoRoller is here: https://skia.googlesource.com/buildbot/+doc/main/autoroll/README.md
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…r#11281) flutter/flutter@d117642...dd64978 2026-03-18 engine-flutter-autoroll@skia.org Roll Skia from 2fb5fa71eb12 to f0a13e5efbad (2 revisions) (flutter/flutter#183830) 2026-03-18 engine-flutter-autoroll@skia.org Roll Skia from ae3d36cb9e29 to 2fb5fa71eb12 (3 revisions) (flutter/flutter#183823) 2026-03-18 94012149+richardexfo@users.noreply.github.com Linux reuse sibling (flutter/flutter#183653) 2026-03-18 engine-flutter-autoroll@skia.org Roll Skia from 84a180a1fa80 to ae3d36cb9e29 (4 revisions) (flutter/flutter#183812) 2026-03-18 1961493+harryterkelsen@users.noreply.github.com fix(web): handle asynchronously disposed platform views (flutter/flutter#183666) 2026-03-17 87018443+mayanksharma9@users.noreply.github.com (Test cross-imports) Remove legacy Material import from sliver_constraints_test (flutter/flutter#183351) 2026-03-17 74057391+jhonathanqz@users.noreply.github.com Fix Android Studio pluginsPath when version is unknown (do not use 0.0) (flutter/flutter#182681) 2026-03-17 50643541+Mairramer@users.noreply.github.com Fixes animation glitch into bottom sheet (flutter/flutter#183303) 2026-03-17 ahmedsameha1@gmail.com Handle#6537 second grouped test (flutter/flutter#182529) 2026-03-17 ahmedsameha1@gmail.com Add a Clarification for the docs of suggestionsBuilder of SearchAnchor (flutter/flutter#183106) 2026-03-17 nate.w5687@gmail.com Remove obsolete null checks from style guide (flutter/flutter#181703) 2026-03-17 jason-simmons@users.noreply.github.com [Impeller] Do not delete the GL object in a HandleGLES if the handle has a cleanup callback (flutter/flutter#183561) 2026-03-17 jason-simmons@users.noreply.github.com Encode source file patches as UTF-8 in the code formatter script (flutter/flutter#183761) 2026-03-17 82673815+gktirkha@users.noreply.github.com Fix widget inspector control layout and add safe area regression test (flutter/flutter#180789) 2026-03-17 43054281+camsim99@users.noreply.github.com Reland "[Android] Add mechanism for setting Android engine flags via Android manifest (take 2)" (flutter/flutter#182522) 2026-03-17 1961493+harryterkelsen@users.noreply.github.com fix(web): fix crash in Skwasm when transferring non-transferable texture sources (flutter/flutter#183799) 2026-03-17 engine-flutter-autoroll@skia.org Roll Skia from dba893a44d7a to 84a180a1fa80 (7 revisions) (flutter/flutter#183803) 2026-03-17 brunocorona.alcantar@gmail.com Framework: Improve DropdownButton selectedItemBuilder assertion (flutter/flutter#183732) 2026-03-17 brunocorona.alcantar@gmail.com Add mainAxisAlignment to NavigationRail (flutter/flutter#183514) 2026-03-17 34871572+gmackall@users.noreply.github.com Update android triage process to not look at unassigned p1s every week (flutter/flutter#183805) 2026-03-17 30870216+gaaclarke@users.noreply.github.com Adds macos impeller new gallery transition perf test. (flutter/flutter#183802) 2026-03-17 1961493+harryterkelsen@users.noreply.github.com fix(web_ui): move prepareToDraw after raster to improve concurrency and stability (flutter/flutter#183791) 2026-03-17 rmacnak@google.com [build] Generate debug info for assembly. (flutter/flutter#183425) 2026-03-17 mdebbar@google.com [web] Fix occasional failure to find Chrome tab (flutter/flutter#183737) If this roll has caused a breakage, revert this CL and stop the roller using the controls here: https://autoroll.skia.org/r/flutter-packages Please CC boetger@google.com,stuartmorgan@google.com on the revert to ensure that a human is aware of the problem. To file a bug in Packages: https://github.com/flutter/flutter/issues/new/choose To report a problem with the AutoRoller itself, please file a bug: https://issues.skia.org/issues/new?component=1389291&template=1850622 Documentation for the AutoRoller is here: https://skia.googlesource.com/buildbot/+doc/main/autoroll/README.md
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…ter#183732) ## Description Added an assertion in `_DropdownButtonState.build` to validate that the list returned by `selectedItemBuilder` has the same length as the `items` list. Previously, a length mismatch caused a cryptic `child != null` or `i == index` assertion failure from the underlying `IndexedStack` during the paint phase. This update catches the error during the build phase and provides developers with a clear, actionable error message. Fixes flutter#92773 ## Pre-launch Checklist - [x] I read the [Contributor Guide] and followed the process outlined there for submitting PRs. - [x] I read the [AI contribution guidelines] and understand my responsibilities, or I am not using AI tools. - [x] I read the [Tree Hygiene] wiki page, which explains my responsibilities. - [x] I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement]. - [x] I signed the [CLA]. - [x] I listed at least one issue that this PR fixes in the description above. - [x] I updated/added relevant documentation (doc comments with `///`). - [x] I added new tests to check the change I am making, or this PR is [test-exempt]. - [x] I followed the [breaking change policy] and added [Data Driven Fixes] where supported. - [x] All existing and new tests are passing. If you need help, consider asking for advice on the #hackers-new channel on [Discord]. **Note**: The Flutter team is currently trialing the use of [Gemini Code Assist for GitHub](https://developers.google.com/gemini-code-assist/docs/review-github-code). Comments from the `gemini-code-assist` bot should not be taken as authoritative feedback from the Flutter team. If you find its comments useful you can update your code accordingly, but if you are unsure or disagree with the feedback, please feel free to wait for a Flutter team member's review for guidance on which automated comments should be addressed. [Contributor Guide]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#overview [AI contribution guidelines]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#ai-contribution-guidelines [Tree Hygiene]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md [test-exempt]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#tests [Flutter Style Guide]: https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md [Features we expect every widget to implement]: https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md#features-we-expect-every-widget-to-implement [CLA]: https://cla.developers.google.com/ [flutter/tests]: https://github.com/flutter/tests [breaking change policy]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#handling-breaking-changes [Discord]: https://github.com/flutter/flutter/blob/main/docs/contributing/Chat.md [Data Driven Fixes]: https://github.com/flutter/flutter/blob/main/docs/contributing/Data-driven-Fixes.md --------- Co-authored-by: Kate Lovett <katelovett@google.com>
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…ter#183732) ## Description Added an assertion in `_DropdownButtonState.build` to validate that the list returned by `selectedItemBuilder` has the same length as the `items` list. Previously, a length mismatch caused a cryptic `child != null` or `i == index` assertion failure from the underlying `IndexedStack` during the paint phase. This update catches the error during the build phase and provides developers with a clear, actionable error message. Fixes flutter#92773 ## Pre-launch Checklist - [x] I read the [Contributor Guide] and followed the process outlined there for submitting PRs. - [x] I read the [AI contribution guidelines] and understand my responsibilities, or I am not using AI tools. - [x] I read the [Tree Hygiene] wiki page, which explains my responsibilities. - [x] I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement]. - [x] I signed the [CLA]. - [x] I listed at least one issue that this PR fixes in the description above. - [x] I updated/added relevant documentation (doc comments with `///`). - [x] I added new tests to check the change I am making, or this PR is [test-exempt]. - [x] I followed the [breaking change policy] and added [Data Driven Fixes] where supported. - [x] All existing and new tests are passing. If you need help, consider asking for advice on the #hackers-new channel on [Discord]. **Note**: The Flutter team is currently trialing the use of [Gemini Code Assist for GitHub](https://developers.google.com/gemini-code-assist/docs/review-github-code). Comments from the `gemini-code-assist` bot should not be taken as authoritative feedback from the Flutter team. If you find its comments useful you can update your code accordingly, but if you are unsure or disagree with the feedback, please feel free to wait for a Flutter team member's review for guidance on which automated comments should be addressed. [Contributor Guide]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#overview [AI contribution guidelines]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#ai-contribution-guidelines [Tree Hygiene]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md [test-exempt]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#tests [Flutter Style Guide]: https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md [Features we expect every widget to implement]: https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md#features-we-expect-every-widget-to-implement [CLA]: https://cla.developers.google.com/ [flutter/tests]: https://github.com/flutter/tests [breaking change policy]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#handling-breaking-changes [Discord]: https://github.com/flutter/flutter/blob/main/docs/contributing/Chat.md [Data Driven Fixes]: https://github.com/flutter/flutter/blob/main/docs/contributing/Data-driven-Fixes.md --------- Co-authored-by: Kate Lovett <katelovett@google.com>
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…r#11281) flutter/flutter@d117642...dd64978 2026-03-18 engine-flutter-autoroll@skia.org Roll Skia from 2fb5fa71eb12 to f0a13e5efbad (2 revisions) (flutter/flutter#183830) 2026-03-18 engine-flutter-autoroll@skia.org Roll Skia from ae3d36cb9e29 to 2fb5fa71eb12 (3 revisions) (flutter/flutter#183823) 2026-03-18 94012149+richardexfo@users.noreply.github.com Linux reuse sibling (flutter/flutter#183653) 2026-03-18 engine-flutter-autoroll@skia.org Roll Skia from 84a180a1fa80 to ae3d36cb9e29 (4 revisions) (flutter/flutter#183812) 2026-03-18 1961493+harryterkelsen@users.noreply.github.com fix(web): handle asynchronously disposed platform views (flutter/flutter#183666) 2026-03-17 87018443+mayanksharma9@users.noreply.github.com (Test cross-imports) Remove legacy Material import from sliver_constraints_test (flutter/flutter#183351) 2026-03-17 74057391+jhonathanqz@users.noreply.github.com Fix Android Studio pluginsPath when version is unknown (do not use 0.0) (flutter/flutter#182681) 2026-03-17 50643541+Mairramer@users.noreply.github.com Fixes animation glitch into bottom sheet (flutter/flutter#183303) 2026-03-17 ahmedsameha1@gmail.com Handle#6537 second grouped test (flutter/flutter#182529) 2026-03-17 ahmedsameha1@gmail.com Add a Clarification for the docs of suggestionsBuilder of SearchAnchor (flutter/flutter#183106) 2026-03-17 nate.w5687@gmail.com Remove obsolete null checks from style guide (flutter/flutter#181703) 2026-03-17 jason-simmons@users.noreply.github.com [Impeller] Do not delete the GL object in a HandleGLES if the handle has a cleanup callback (flutter/flutter#183561) 2026-03-17 jason-simmons@users.noreply.github.com Encode source file patches as UTF-8 in the code formatter script (flutter/flutter#183761) 2026-03-17 82673815+gktirkha@users.noreply.github.com Fix widget inspector control layout and add safe area regression test (flutter/flutter#180789) 2026-03-17 43054281+camsim99@users.noreply.github.com Reland "[Android] Add mechanism for setting Android engine flags via Android manifest (take 2)" (flutter/flutter#182522) 2026-03-17 1961493+harryterkelsen@users.noreply.github.com fix(web): fix crash in Skwasm when transferring non-transferable texture sources (flutter/flutter#183799) 2026-03-17 engine-flutter-autoroll@skia.org Roll Skia from dba893a44d7a to 84a180a1fa80 (7 revisions) (flutter/flutter#183803) 2026-03-17 brunocorona.alcantar@gmail.com Framework: Improve DropdownButton selectedItemBuilder assertion (flutter/flutter#183732) 2026-03-17 brunocorona.alcantar@gmail.com Add mainAxisAlignment to NavigationRail (flutter/flutter#183514) 2026-03-17 34871572+gmackall@users.noreply.github.com Update android triage process to not look at unassigned p1s every week (flutter/flutter#183805) 2026-03-17 30870216+gaaclarke@users.noreply.github.com Adds macos impeller new gallery transition perf test. (flutter/flutter#183802) 2026-03-17 1961493+harryterkelsen@users.noreply.github.com fix(web_ui): move prepareToDraw after raster to improve concurrency and stability (flutter/flutter#183791) 2026-03-17 rmacnak@google.com [build] Generate debug info for assembly. (flutter/flutter#183425) 2026-03-17 mdebbar@google.com [web] Fix occasional failure to find Chrome tab (flutter/flutter#183737) If this roll has caused a breakage, revert this CL and stop the roller using the controls here: https://autoroll.skia.org/r/flutter-packages Please CC boetger@google.com,stuartmorgan@google.com on the revert to ensure that a human is aware of the problem. To file a bug in Packages: https://github.com/flutter/flutter/issues/new/choose To report a problem with the AutoRoller itself, please file a bug: https://issues.skia.org/issues/new?component=1389291&template=1850622 Documentation for the AutoRoller is here: https://skia.googlesource.com/buildbot/+doc/main/autoroll/README.md
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Description
Added an assertion in
_DropdownButtonState.buildto validate that the list returned byselectedItemBuilderhas the same length as theitemslist.Previously, a length mismatch caused a cryptic
child != nullori == indexassertion failure from the underlyingIndexedStackduring the paint phase. This update catches the error during the build phase and provides developers with a clear, actionable error message.Fixes #92773
Pre-launch Checklist
///).If you need help, consider asking for advice on the #hackers-new channel on Discord.
Note: The Flutter team is currently trialing the use of Gemini Code Assist for GitHub. Comments from the
gemini-code-assistbot should not be taken as authoritative feedback from the Flutter team. If you find its comments useful you can update your code accordingly, but if you are unsure or disagree with the feedback, please feel free to wait for a Flutter team member's review for guidance on which automated comments should be addressed.