Add PlatformDispatcher.onAlwaysUse24HourFormatChanged callback by prasad2512 · Pull Request #194670 · flutter/flutter

prasad2512 · 2026-10-18T06:53:55Z

Part of #194637

Pre-launch Checklist

I read the Contributor Guide and followed the process outlined there for submitting PRs.
I read the Tree Hygiene wiki page, which explains my responsibilities.
I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
I signed the CLA.
I listed at least one issue that this PR fixes in the description above.
I updated/added relevant documentation (doc comments with ///).
I added new tests to check the change I am making, or this PR is test-exempt.
All existing and new tests are passing.

Description

This PR introduces the engine API foundation for tracking platform 24-hour time format changes at runtime (split from the original full-stack PR per review feedback).

Changes

dart:ui.PlatformDispatcher:
- Added onAlwaysUse24HourFormatChanged callback getter, setter, and zone tracking.
- Updated _updateUserSettingsData to invoke onAlwaysUse24HourFormatChanged whenever alwaysUse24HourFormat changes.
- Added documentation comments to alwaysUse24HourFormat referencing the new callback.
Web Engine (lib/web_ui):
- Added onAlwaysUse24HourFormatChanged to PlatformDispatcher interface and EnginePlatformDispatcher implementation.
- Implemented invokeOnAlwaysUse24HourFormatChanged() with zone preservation.
- Added unit tests in platform_dispatcher_test.dart verifying callback invocation and zone preservation with per-test isolated dispatcher.
Framework Debug Overrides (packages/flutter):
- Updated _debugNotifyViewMetricsOverrideChanged in debug.dart to forward onAlwaysUse24HourFormatChanged.
- Updated comments in debug.dart to reflect that alwaysUse24HourFormat now announces through onAlwaysUse24HourFormatChanged.
- Updated _DebugViewMetricsPlatformDispatcher and tests in debug_view_metrics_override_test.dart.
Engine Unit Tests:
- Added unit test in engine/src/flutter/lib/ui/fixtures/ui_test.dart verifying that onAlwaysUse24HourFormatChanged is invoked only when alwaysUse24HourFormat changes, and remains unaffected by unrelated settings. Cleaned up dispatcher callback at test completion.

Note: Framework layer integration (WidgetsBindingObserver.didChangeAlwaysUse24HourFormat and MediaQuery updates) will follow in Part 2 once this engine API lands.

google-cla · 2026-10-18T06:54:07Z

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Code Review

This pull request adds support for handling platform configuration changes, such as 24-hour format updates, by registering a callback on the PlatformDispatcher and propagating it through WidgetsBindingObserver to update MediaQuery dynamically. Feedback points out an unresolved documentation reference to alwaysUse24HourFormat in RendererBinding, suggesting it should be qualified as PlatformDispatcher.alwaysUse24HourFormat to resolve correctly.

prasad2512 · 2026-10-18T08:05:39Z

Addressed doc reference review feedback in commit 00c9f72:

Qualified [PlatformDispatcher.alwaysUse24HourFormat] in packages/flutter/lib/src/rendering/binding.dart so it resolves properly in generated dartdoc.

prasad2512 · 2026-10-18T08:25:27Z

@googlebot I signed it!

prasad2512 · 2026-10-19T17:47:22Z

@googlebot I signed it!

chunhtai

LGTM, just minor comment on the doc

…changes (fixes flutter#194637)

…aysUse24HourFormat

victorsanni · 2026-10-27T16:46:02Z

Hi, is this ready for another review? If yes, please remember to request a review so this goes back in the review queue.

prasad2512 · 2026-10-27T16:53:51Z

@victorsanni Yes, it is ready for review! The doc comment feedback from @chunhtai has been addressed in commit 4e2375a. Thanks!

chunhtai · 2026-10-27T16:18:55Z

+  ///
+  /// This method exposes notifications from
+  /// [dart:ui.PlatformDispatcher.onPlatformConfigurationChanged].
+  void didChangePlatformConfiguration() {}


actually looking into the code closer, most of the property platform configuration is exposed individually in widgetbindingObserver.

I think we should directly expose the alwaysUse24HourFormat to something like

didChange24HourFormat

This will make it clear on what property has changed.

that way, we don't need to worry about people not knowing what actually changed if we exposed didChangePlatformConfiguration directly

Thanks @chunhtai! That makes total sense and fits the existing WidgetsBindingObserver pattern much better. Updated to didChange24HourFormat in commit 0d17efa, along with updated docs, MediaQuery observer callback, and test cases.

…dback

chunhtai · 2026-10-28T22:44:48Z

+    super.handlePlatformConfigurationChanged();
+    for (final observer in List<WidgetsBindingObserver>.of(_observers)) {
+      try {
+        observer.didChange24HourFormat();


This doesn't look right, handlePlatformConfigurationChanged will be called when any of the configuration change. so even if the alwaysUse24HourFormat didn't change, the observer may still be notified.

Great catch! We've added value-diff tracking via _alwaysUse24HourFormat in WidgetsBinding. Now handlePlatformConfigurationChanged checks if (_alwaysUse24HourFormat == currentAlwaysUse24HourFormat) return;, ensuring WidgetsBindingObserver.didChange24HourFormat() is strictly only dispatched when alwaysUse24HourFormat actually changes and not for other unrelated configuration updates.

Updated in commit 85de8fb with unit tests verifying that invoking handlePlatformConfigurationChanged() without an alwaysUse24HourFormat change does not notify observers.

chunhtai · 2026-10-28T22:46:18Z

      ..onTextScaleFactorChanged = handleTextScaleFactorChanged
-      ..onPlatformBrightnessChanged = handlePlatformBrightnessChanged;
+      ..onPlatformBrightnessChanged = handlePlatformBrightnessChanged
+      ..onPlatformConfigurationChanged = handlePlatformConfigurationChanged;


We should create a new API in platformdispatcher for 24hourformat just like onplatformbirightnessChanged

Agreed! Having a dedicated onAlwaysUse24HourFormatChanged callback in PlatformDispatcher (matching onPlatformBrightnessChanged, onTextScaleFactorChanged, etc.) would be the cleanest long-term API on the engine side.

Since PlatformDispatcher lives in dart:ui (flutter/engine) and currently only dispatches onPlatformConfigurationChanged for 24-hour format updates (see also foundation/debug.dart:606), we've implemented the value-diff guard in WidgetsBinding (commit 85de8fb) so the framework never dispatches false notifications when other configuration changes occur. Would you like us to also open an engine PR for onAlwaysUse24HourFormatChanged?

yes, we should do that, and also you can do this in the same pr

Done in commit 4c056b8!

Implemented onAlwaysUse24HourFormatChanged in PlatformDispatcher (both native dart:ui and web_ui).

Registered handleAlwaysUse24HourFormatChanged in RendererBinding to directly observe the new callback.

Updated WidgetsBinding to dispatch didChange24HourFormat to observers via the dedicated handler, eliminating the manual value-diffing workaround.

Updated TestPlatformDispatcher and added unit tests in ui_test.dart, window_test.dart, �inding_test.dart, and platform_dispatcher_test.dart.

Thanks for the guidance! Ready for re-review.

Avoid notifying WidgetsBindingObserver.didChange24HourFormat when handlePlatformConfigurationChanged is triggered by unrelated platform configuration changes. Track _alwaysUse24HourFormat in WidgetsBinding and add unit tests to verify.

…view feedback

flutter-dashboard · 2026-11-05T22:23:09Z

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Changes reported for pull request #194670 at sha 9306f3c

chunhtai

LGTM

auto-submit · 2026-11-06T01:39:29Z

autosubmit label was removed for flutter/flutter/194670, because - The status or check suite Dashboard Checks has failed. Please fix the issues identified (or deflake) before re-applying this label.

prasad2512 · 2026-11-06T02:02:55Z

Hi @chunhtai and @victorsanni,

All engine, web, and framework widget tests are passing cleanly across platforms, and Skia Gold has 0 untriaged images.

The single failure in Mac mac_ios_debug_unopt_sim_arm64 is due to the known flaky test tracked in #194252 (-[FlutterViewControllerTest testViewWillTransitionToSize_DoesDelayEngineCallIfNonZeroDuration]).

Could someone please trigger a rerun of this job on the dashboard and re-apply the autosubmit label? Thank you!

chunhtai

LGTM

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Comment thread packages/flutter/lib/src/rendering/binding.dart Resolved

prasad2512 force-pushed the fix/issue-194637-refresh-always-use-24-hour branch from 00c9f72 to 04b3df8 Compare October 19, 2026 17:47

prasad2512 force-pushed the fix/issue-194637-refresh-always-use-24-hour branch from 04b3df8 to 415849f Compare October 19, 2026 17:49

Renzo-Olivares requested review from chunhtai and victorsanni October 20, 2026 23:23

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Comment thread packages/flutter/lib/src/widgets/binding.dart Resolved

victorsanni added the CICD Run CI/CD label Oct 27, 2026

prasad2512 added 3 commits October 27, 2026 14:36

Refresh MediaQuery.alwaysUse24HourFormat when platform configuration …

f2da993

…changes (fixes flutter#194637)

Qualify alwaysUse24HourFormat doc reference as PlatformDispatcher.alw…

7f6da59

…aysUse24HourFormat

List PlatformDispatcher properties in didChangePlatformConfiguration doc

4e2375a

prasad2512 dismissed chunhtai’s stale review via 4e2375a October 27, 2026 09:07

prasad2512 force-pushed the fix/issue-194637-refresh-always-use-24-hour branch from 415849f to 4e2375a Compare October 27, 2026 09:07

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Expose didChange24HourFormat in WidgetsBindingObserver per review fee…

0d17efa

…dback

prasad2512 requested a review from chunhtai October 28, 2026 01:51

chunhtai reviewed Oct 28, 2026

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prasad2512 requested a review from chunhtai October 29, 2026 05:09

Add PlatformDispatcher.onAlwaysUse24HourFormatChanged callback per re…

4c056b8

…view feedback

github-actions Bot added the engine flutter/engine related. See also e: labels. label Oct 29, 2026

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Merge branch 'master' into fix/issue-194637-refresh-always-use-24-hour

9306f3c

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prasad2512 requested a review from victorsanni November 5, 2026 22:30

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Merge branch 'master' into fix/issue-194637-refresh-always-use-24-hour

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prasad2512 requested review from chunhtai and victorsanni November 6, 2026 02:04

Merge branch 'master' into fix/issue-194637-refresh-always-use-24-hour

8bac733

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Merged via the queue into flutter:master with commit fabacd6 Nov 6, 2026
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prasad2512 mentioned this pull request Nov 6, 2026

Add didChangeAlwaysUse24HourFormat to WidgetsBinding and update MediaQuery #196117

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justinmc mentioned this pull request Nov 6, 2026

Flutter Notable Commits - 2026 #181433

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engine-flutter-autoroll mentioned this pull request Nov 7, 2026

Roll Flutter from 09175cdeac89 to e36b37012875 (22 revisions) flutter/packages#13586

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