[web] Fix SemanticsService.announce not working inside dialogs by flutter-zl · Pull Request #179958 · flutter/flutter

flutter-zl · 2025-12-16T21:27:10Z

Solution
When a modal dialog is present, temporarily move the existing aria-live element inside the modal dialog before making the announcement, then move it back afterward. A small delay is also added to allow VoiceOver to finish reading the button's accessible name first.

Demo
Before (bug): https://flutter-demo-03-before.web.app
After (fix): https://flutter-demo-03-after.web.app

Testing
Enable VoiceOver (Cmd+F5 on macOS)
Open a dialog and click the "Announce" button
Verify the announcement is spoken after the button label

Next step
Filing a follow-up issue for: Adding a delay parameter to SemanticsService.announce() API for developers who need custom delays for long button labels

mdebbar · 2026-01-06T20:52:01Z

engine/src/flutter/lib/web_ui/lib/src/engine/semantics/accessibility.dart

+    Timer(announcementDelay, () {
+      ariaLiveElement.text = messageText;
+    });


I'm not sure that I fully understand this delay. I would think that when we receive a request to announce something, we should announce it immediately.

When a user clicks a button that triggers an announcement, voiceOver immediately starts reading the button's accessible name (for example, "Announce, button"). If we set the aria-live text immediately, VoiceOver tries to announce it at the same time. VoiceOver gets confused and drops one of the announcements (usually the aria-live one).The 500ms delay gives VoiceOver time to finish reading the button label before we inject the announcement text.

Without delay:
User clicks "Announce" button
VoiceOver: "Announce, button" ← aria-live update happens here, gets dropped
(silence - announcement lost)

With delay:
User clicks "Announce" button
VoiceOver: "Announce, button"
(500ms pause)
VoiceOver: "Your announcement message"

I did some investigation and it turns out we do not need the 500ms delay value.

Investigation: Through systematic testing with different delay values (500ms → 100ms → 50ms → 20ms → 10ms → 5ms → 1ms → 0ms), I discovered:

0ms (synchronous): Doesn't work - VoiceOver doesn't announce

Duration.zero with Timer: Works - VoiceOver announces correctly

Root Cause: VoiceOver needs the aria-live text to be set in a different event loop tick than the button click. Setting it synchronously interferes with VoiceOver's internal speech queue processing.

Fix: Use Timer(Duration.zero, ...) to defer setting the announcement text to the next event loop iteration.
This provides the minimum necessary delay.

Please check https://flutter-demo-03-after.web.app/

mdebbar

flutter/flutter#179958)

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(flutter/flutter#178102) 2026-01-08 [email protected] Fix iOS xattr removal to clear all extended attributes (flutter/flutter#180355) 2026-01-08 [email protected] [ Widget Preview ] Move widget_preview_scaffold tests to `dev/integration_tests/widget_preview_scaffold` (flutter/flutter#180658) 2026-01-08 [email protected] De-interleaves engine dart test output (flutter/flutter#180651) 2026-01-08 [email protected] [web] Fix SemanticsService.announce not working inside dialogs (flutter/flutter#179958) 2026-01-08 [email protected] Roll Skia from 42233226ac56 to 837be28dd218 (2 revisions) (flutter/flutter#180693) 2026-01-08 [email protected] Roll Dart SDK to 3.11.0-296.2.beta (flutter/flutter#180685) 2026-01-08 [email protected] Improve code quality in `AndroidTouchProcessorTest.java` (flutter/flutter#180583) 2026-01-08 [email protected] Revert "Reverts "[reland] Unify canvas creation and Surface code in S…kwasm and CanvasKit (#179473)" (#180152)" (flutter/flutter#180610) 2026-01-08 [email protected] Roll Skia from a0c407bce408 to 42233226ac56 (4 revisions) (flutter/flutter#180688) 2026-01-08 [email protected] [ Tool ] Fix flake in overall_experience_test.dart (flutter/flutter#180655) 2026-01-08 [email protected] Roll Packages from 9705815 to 039a026 (6 revisions) (flutter/flutter#180684) 2026-01-08 [email protected] flutter_tools: Auto-generate ExportOptions.plist for manual iOS code signing (flutter/flutter#177888) 2026-01-08 [email protected] Roll Skia from 58837e160874 to a0c407bce408 (2 revisions) (flutter/flutter#180679) 2026-01-08 [email protected] Roll Skia from 1e3266fdba86 to 58837e160874 (1 revision) (flutter/flutter#180677) 2026-01-08 [email protected] Roll Skia from 3c47ea10638f to 1e3266fdba86 (4 revisions) (flutter/flutter#180675) 2026-01-08 [email protected] Roll Fuchsia Linux SDK from dTvN_JVSCfGFRasvH... to rxeg-6UB678HKJ4UQ... (flutter/flutter#180673) ...

flutter/flutter#179958)

[web] Fix SemanticsService.announce not working inside dialogs

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github-actions bot added engine flutter/engine related. See also e: labels. a: accessibility Accessibility, e.g. VoiceOver or TalkBack. (aka a11y) platform-web Web applications specifically labels Dec 16, 2025

flutter-zl added 2 commits December 16, 2025 13:27

Merge remote-tracking branch 'origin/master' into issue_179076

c35e924

Add tests for modal dialog announcements

819bfdc

flutter-zl requested a review from mdebbar December 17, 2025 19:13

flutter-zl marked this pull request as ready for review December 17, 2025 19:13

flutter-zl mentioned this pull request Dec 20, 2025

Adding a delay parameter to SemanticsService.announce() API for developers who need custom delays for long button labels #180156

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mdebbar reviewed Jan 6, 2026

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flutter-zl requested a review from mdebbar January 7, 2026 04:57

flutter-zl added 2 commits January 7, 2026 21:41

[web] Use Timer(Duration.zero) for aria-live announcements

eabfa50

Merge remote-tracking branch 'origin/master' into issue_179076

2175fa2

mdebbar approved these changes Jan 8, 2026

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flutter-zl added the autosubmit Merge PR when tree becomes green via auto submit App label Jan 8, 2026

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Merged via the queue into flutter:master with commit 773923a Jan 8, 2026
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Roll Flutter from 01d37bc80fd5 to 96403e0fa570 (41 revisions) flutter/packages#10756

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773923a [web] Fix SemanticsService.announce not working inside dialogs (

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flutter/flutter#179958)

engine-flutter-autoroll added a commit to engine-flutter-autoroll/packages that referenced this pull request Jan 9, 2026

773923a [web] Fix SemanticsService.announce not working inside dialogs (

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flutter/flutter#179958)

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Roll Flutter from 01d37bc80fd5 to c1e1dc260fb7 (43 revisions) flutter/packages#10757

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Roll Flutter from 01d37bc80fd5 to fd1fad23f595 (44 revisions) flutter/packages#10759

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engine-flutter-autoroll added a commit to engine-flutter-autoroll/packages that referenced this pull request Jan 9, 2026

773923a [web] Fix SemanticsService.announce not working inside dialogs (

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flutter/flutter#179958)

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Roll Flutter from 01d37bc80fd5 to 61b241292e19 (45 revisions) flutter/packages#10760

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773923a [web] Fix SemanticsService.announce not working inside dialogs (

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flutter/flutter#179958)

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Roll Flutter from 01d37bc80fd5 to 0b7596b3f269 (64 revisions) flutter/packages#10768

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773923a [web] Fix SemanticsService.announce not working inside dialogs (

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flutter/flutter#179958)

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Roll Flutter from 01d37bc80fd5 to 73769a220639 (65 revisions) flutter/packages#10769

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773923a [web] Fix SemanticsService.announce not working inside dialogs (

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flutter/flutter#179958)

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Roll Flutter from 01d37bc80fd5 to 73769a220639 (65 revisions) flutter/packages#10770

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engine-flutter-autoroll added a commit to engine-flutter-autoroll/packages that referenced this pull request Jan 10, 2026

773923a [web] Fix SemanticsService.announce not working inside dialogs (

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flutter/flutter#179958)

engine-flutter-autoroll added a commit to engine-flutter-autoroll/packages that referenced this pull request Feb 11, 2026

773923a [web] Fix SemanticsService.announce not working inside dialogs (

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flutter/flutter#179958)

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[web] Fix SemanticsService.announce not working inside dialogs#179958

[web] Fix SemanticsService.announce not working inside dialogs#179958
auto-submit[bot] merged 5 commits intoflutter:masterfrom
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flutter-zl commented Dec 16, 2025 •

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