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 <[email protected]>
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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 [email protected] Roll Skia from 2fb5fa71eb12 to f0a13e5efbad (2 revisions) (flutter/flutter#183830) 2026-03-18 [email protected] Roll Skia from ae3d36cb9e29 to 2fb5fa71eb12 (3 revisions) (flutter/flutter#183823) 2026-03-18 [email protected] Linux reuse sibling (flutter/flutter#183653) 2026-03-18 [email protected] Roll Skia from 84a180a1fa80 to ae3d36cb9e29 (4 revisions) (flutter/flutter#183812) 2026-03-18 [email protected] fix(web): handle asynchronously disposed platform views (flutter/flutter#183666) 2026-03-17 [email protected] (Test cross-imports) Remove legacy Material import from sliver_constraints_test (flutter/flutter#183351) 2026-03-17 [email protected] Fix Android Studio pluginsPath when version is unknown (do not use 0.0) (flutter/flutter#182681) 2026-03-17 [email protected] Fixes animation glitch into bottom sheet (flutter/flutter#183303) 2026-03-17 [email protected] Handle#6537 second grouped test (flutter/flutter#182529) 2026-03-17 [email protected] Add a Clarification for the docs of suggestionsBuilder of SearchAnchor (flutter/flutter#183106) 2026-03-17 [email protected] Remove obsolete null checks from style guide (flutter/flutter#181703) 2026-03-17 [email protected] [Impeller] Do not delete the GL object in a HandleGLES if the handle has a cleanup callback (flutter/flutter#183561) 2026-03-17 [email protected] Encode source file patches as UTF-8 in the code formatter script (flutter/flutter#183761) 2026-03-17 [email protected] Fix widget inspector control layout and add safe area regression test (flutter/flutter#180789) 2026-03-17 [email protected] Reland "[Android] Add mechanism for setting Android engine flags via Android manifest (take 2)" (flutter/flutter#182522) 2026-03-17 [email protected] fix(web): fix crash in Skwasm when transferring non-transferable texture sources (flutter/flutter#183799) 2026-03-17 [email protected] Roll Skia from dba893a44d7a to 84a180a1fa80 (7 revisions) (flutter/flutter#183803) 2026-03-17 [email protected] Framework: Improve DropdownButton selectedItemBuilder assertion (flutter/flutter#183732) 2026-03-17 [email protected] Add mainAxisAlignment to NavigationRail (flutter/flutter#183514) 2026-03-17 [email protected] Update android triage process to not look at unassigned p1s every week (flutter/flutter#183805) 2026-03-17 [email protected] Adds macos impeller new gallery transition perf test. (flutter/flutter#183802) 2026-03-17 [email protected] fix(web_ui): move prepareToDraw after raster to improve concurrency and stability (flutter/flutter#183791) 2026-03-17 [email protected] [build] Generate debug info for assembly. (flutter/flutter#183425) 2026-03-17 [email protected] [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 [email protected],[email protected] 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
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