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[Web][Engine] Update MediaQuery in response to semanticsEnabled #166836

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Merged
auto-submit merged 11 commits into from
Jun 2, 2025
Merged

[Web][Engine] Update MediaQuery in response to semanticsEnabled #166836

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8646164
fix: Call invokeOnAccessibilityFeaturesChanged
koji-1009 Apr 11, 2025
9e447ab
test: onAccessibilityFeaturesChanged is executed when semantics is en…
koji-1009 Apr 12, 2025
a51f4c5
feat: Future.microtask
koji-1009 May 3, 2025
322d936
refactor: Avoid execution during build time
koji-1009 May 8, 2025
44d3b5b
test: Fix test cases
koji-1009 May 10, 2025
26f33c6
Merge branch 'master' into fix/accessible_navigation
koji-1009 May 10, 2025
1792c9f
refactor: Check schedulerPhase
koji-1009 May 22, 2025
1d70e07
Update packages/flutter/lib/src/semantics/binding.dart
koji-1009 May 22, 2025
4154822
Merge branch 'master' into fix/accessible_navigation
koji-1009 May 28, 2025
0be2b0e
Merge branch 'master' into fix/accessible_navigation
koji-1009 May 30, 2025
fea54cf
Update engine/src/flutter/lib/web_ui/test/engine/window_test.dart
koji-1009 May 30, 2025
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1 change: 1 addition & 0 deletions engine/src/flutter/lib/web_ui/lib/src/engine/semantics/semantics.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -2485,6 +2485,7 @@ class EngineSemantics {
final PlatformConfiguration newConfiguration = EnginePlatformDispatcher.instance.configuration
.copyWith(accessibilityFeatures: original.copyWith(accessibleNavigation: value));
EnginePlatformDispatcher.instance.configuration = newConfiguration;
EnginePlatformDispatcher.instance.invokeOnAccessibilityFeaturesChanged();

_semanticsEnabled = value;

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13 changes: 13 additions & 0 deletions engine/src/flutter/lib/web_ui/test/engine/window_test.dart
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Expand Up @@ -334,6 +334,19 @@ Future<void> testMain() async {
EnginePlatformDispatcher.instance.invokeOnAccessibilityFeaturesChanged();
});

test('onAccessibilityFeaturesChanged is called when semantics is enabled', () {
bool a11yChangeInvoked = false;
myWindow.onAccessibilityFeaturesChanged = () {
a11yChangeInvoked = true;
};

expect(EngineSemantics.instance.semanticsEnabled, isFalse);
EngineSemantics.instance.semanticsEnabled = true;

expect(EngineSemantics.instance.semanticsEnabled, isTrue);
expect(a11yChangeInvoked, isTrue);
});

test('onPlatformMessage preserves the zone', () {
final Zone innerZone = Zone.current.fork();

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13 changes: 12 additions & 1 deletion packages/flutter/lib/src/semantics/binding.dart
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Expand Up @@ -10,6 +10,7 @@ library;
import 'dart:ui' as ui show AccessibilityFeatures, SemanticsActionEvent, SemanticsUpdateBuilder;

import 'package:flutter/foundation.dart';
import 'package:flutter/scheduler.dart';
import 'package:flutter/services.dart';

import 'debug.dart';
Expand All @@ -26,7 +27,17 @@ mixin SemanticsBinding on BindingBase {
platformDispatcher
..onSemanticsEnabledChanged = _handleSemanticsEnabledChanged
..onSemanticsActionEvent = _handleSemanticsActionEvent
..onAccessibilityFeaturesChanged = handleAccessibilityFeaturesChanged;
..onAccessibilityFeaturesChanged = () {
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@chunhtai chunhtai May 16, 2025

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We should do this in Widget MediaQuery, not all the listener here care about build phase.

Also when mediaQuery handles it, it should use postframecallback

    if (SchedulerBinding.instance.schedulerPhase == SchedulerPhase.persistentCallbacks) {
      SchedulerBinding.instance.addPostFrameCallback((Duration duration) {
        // do the thing.
      }, debugLabel: 'some meaningful label');
    } else {
      // do the thing
    }

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@koji-1009 koji-1009 May 16, 2025

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I think shuld all listeners be guarded from the build phase.

If we handle to do this on the MediaQuery side, we would call addPostFrameCallback in the didChangeAccessibilityFeatures.
https://github.com/flutter/flutter/blob/3.29.3/packages/flutter/lib/src/widgets/media_query.dart#L1905-L1914

didChangeAccessibilityFeatures is public API, so app developers can use this. Therefore, all code that uses didChangeAccessibilityFeatures will need to be modified.
https://api.flutter.dev/flutter/widgets/WidgetsBindingObserver/didChangeAccessibilityFeatures.html

If we do the build phase for listeners, there will be no breaking change to the public api. Since this breaking change affects only the web, it is difficult to notice and to understand why it is necessary.

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@chunhtai chunhtai May 21, 2025

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this will only happen if the ensureSemantics is called during build phase right? I think this is not a common use case. Now i think we may not even need to have this check. the correct fix will be move ensureSemantics to either a postframecallback or somewhere before runApp

void main() {
  WidgetFlutterBindings.ensureInitialized().ensureSemantics();
  runApp(...)
}

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@koji-1009 koji-1009 May 21, 2025 •
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The problem occurred with the example code. I don't have that much experience with accessibility implementations, so let me ask: is calling the ensureSemantics method on a Button's onTap a non-recommended implementation?

import 'package:flutter/material.dart';
import 'package:flutter/semantics.dart';

void main() {
  runApp(const MaterialApp(home: MyHomePage()));
}

class MyHomePage extends StatelessWidget {
  const MyHomePage({super.key});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            ElevatedButton(
              onPressed: () {
                SemanticsBinding.instance.ensureSemantics();
              },
              child: const Text('Enable a11y'),
            ),
            const SizedBox(height: 24),
            ElevatedButton(
              onPressed: () {
                ScaffoldMessenger.of(context).showSnackBar(
                  SnackBar(
                    content: const Text('Should stay visible'),
                    action: SnackBarAction(label: 'Action', onPressed: () {}),
                  ),
                );
              },
              child: const Text('Show snackbar'),
            ),
            const SizedBox(height: 24),
            Text(
              'MediaQuery.accessibleNavigationOf(context): ${MediaQuery.accessibleNavigationOf(context)}',
            ),
            Text(
              'SemanticsBinding.instance.semanticsEnabled: ${SemanticsBinding.instance.semanticsEnabled}',
            ),
            Text(
              'SemanticsBinding.instance.platformDispatcher.semanticsEnabled: ${SemanticsBinding.instance.platformDispatcher.semanticsEnabled}',
            ),
            Text(
              'SemanticsBinding.instance.accessibilityFeatures: ${SemanticsBinding.instance.accessibilityFeatures}',
            ),
          ],
        ),
      ),
    );
  }
}

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@chunhtai chunhtai May 21, 2025

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ok i see the issue now, this is mostly a web issue that it enable the semantics in updatesemantics instead of synchronously when ensureSemanitcs is called.

Can you convert the microtask here to check schedule phase and postframe callback, and add a todo to link to this issue #158399

That way we can clean it up later when i fix the web engine

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@koji-1009 koji-1009 May 21, 2025

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OK, I'll do it. Thanks for the review.

// TODO(chunhtai): Web should not notify accessibility feature changes during updateSemantics
// https://github.com/flutter/flutter/issues/158399
if (SchedulerBinding.instance.schedulerPhase == SchedulerPhase.persistentCallbacks) {
SchedulerBinding.instance.addPostFrameCallback((Duration duration) {
handleAccessibilityFeaturesChanged();
}, debugLabel: 'SemanticsBinding.handleAccessibilityFeaturesChanged');
} else {
handleAccessibilityFeaturesChanged();
}
};
_handleSemanticsEnabledChanged();
}

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2 changes: 1 addition & 1 deletion packages/flutter/test/material/app_test.dart
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Expand Up @@ -425,7 +425,7 @@ void main() {
// didChangeAccessibilityFeatures
tester.platformDispatcher.accessibilityFeaturesTestValue = FakeAccessibilityFeatures.allOn;

await tester.pump();
await tester.pumpAndSettle();

expect(routeBuildCount, equals(1));
expect(dependentBuildCount, equals(5));
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4 changes: 2 additions & 2 deletions packages/flutter/test/widgets/media_query_test.dart
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Expand Up @@ -451,7 +451,7 @@ void main() {

expect(data.accessibleNavigation, true);
tester.platformDispatcher.accessibilityFeaturesTestValue = const FakeAccessibilityFeatures();
await tester.pump();
await tester.pumpAndSettle();
expect(data.accessibleNavigation, false);
expect(rebuildCount, 4);

Expand Down Expand Up @@ -512,7 +512,7 @@ void main() {

expect(data.accessibleNavigation, true);
tester.platformDispatcher.accessibilityFeaturesTestValue = const FakeAccessibilityFeatures();
await tester.pump();
await tester.pumpAndSettle();
expect(data.accessibleNavigation, true);
expect(rebuildCount, 1);

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