fix: Resolve memory leak in image_list example by Okikday · Pull Request #189526 · flutter/flutter

Okikday · 2026-07-15T19:22:10Z

This PR resolves a memory leak and cleans up naming conventions in the image_list Devicelab benchmark example.

What is changing:

Moved the AnimationController instantiation out of the build method and into a late final variable to prevent redundant instantiation.
Added a dispose() method to properly clean up the controllers.

Why:
Previously, 50 new controllers were being instantiated on every setState trigger without ever being disposed, causing a memory leak. This refactor correctly manages the widget lifecycle while preserving the underlying performance benchmark (by appending ..repeat() to the initialization so the UI thread remains appropriately stressed).

This PR fixes a trivial lifecycle and styling issue in a devicelab test script. No open issue is associated.

Pre-launch Checklist

flutter-dashboard · 2026-07-15T19:22:14Z

It looks like this pull request may not have tests. Please make sure to add tests or get an explicit test exemption before merging.

If you are not sure if you need tests, consider this rule of thumb: the purpose of a test is to make sure someone doesn't accidentally revert the fix. Ask yourself, is there anything in your PR that you feel it is important we not accidentally revert back to how it was before your fix?

Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing. If you believe this PR qualifies for a test exemption, contact "@test-exemption-reviewer" in the #hackers channel in Discord (don't just cc them here, they won't see it!). The test exemption team is a small volunteer group, so all reviewers should feel empowered to ask for tests, without delegating that responsibility entirely to the test exemption group.

google-cla · 2026-07-15T19:22:20Z

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gemini-code-assist

Code Review

This pull request refactors the image_list example by renaming variables for style consistency and moving the initialization of AnimationControllers from the build method to a class-level field, adding a dispose method to clean them up. Feedback recommends initializing the controllers in initState instead of using a late final field to prevent unnecessary resource allocation during lazy initialization in dispose, and renaming the field to _controllers to follow Dart private naming conventions.

gemini-code-assist · 2026-07-15T19:23:05Z

+  late final controllers = <AnimationController>[
+    for (int i = 0; i < imagesCount; i++)
+      AnimationController(
+        duration: const Duration(milliseconds: 3600),
+        vsync: this,
+      )..repeat(),
+  ];
+
+  @override
+  void dispose() {
+    for (final controller in controllers) {
+      controller.dispose();
+    }
+    super.dispose();
+  }


Using a late final field initializer for controllers can lead to unnecessary resource allocation during widget disposal. If the widget is disposed before it is ever built (e.g., in certain test scenarios or rapid navigation), accessing controllers in dispose() will trigger its lazy initialization. This creates and starts 50 AnimationControllers only to immediately dispose of them.

Additionally, to conform to Dart private naming conventions (consistent with _counter), the field should be prefixed with an underscore (_controllers).

It is highly recommended to initialize the controllers in initState() instead.

late final List<AnimationController> _controllers; @override void initState() { super.initState(); _controllers = <AnimationController>[ for (int i = 0; i < imagesCount; i++) AnimationController( duration: const Duration(milliseconds: 3600), vsync: this, )..repeat(), ]; } @override void dispose() { for (final controller in _controllers) { controller.dispose(); } super.dispose(); }

References

Effective Dart: Style recommends prefixing private identifiers with an underscore. ^(link)

Can you address this feedback and add a test to validate the memory leak has been fixed?

Sure. I will do that in a moment.

Can you address this feedback and add a test to validate the memory leak has been fixed?

Done!. Added the tests to validate that no memory leaks, and also fixed the one line lint warning I missed earlier after running 'flutter analyze'

Piinks · 2026-10-27T22:30:09Z

  final ByteData byteData = await rootBundle.load('images/coast.jpg');
  httpServer.listen((HttpRequest request) async {
-    const chunk_size = 2048;
+    const chunkSize = 2048;


Can you remove the changes here unrelated to the actual bug fix, like changing variable names?

Sure, I can do just that.

Can you remove the changes here unrelated to the actual bug fix, like changing variable names?

Done!

flutter-dashboard · 2026-10-27T22:48:40Z

It looks like this pull request may not have tests. Please make sure to add tests or get an explicit test exemption before merging.

If you are not sure if you need tests, consider this rule of thumb: the purpose of a test is to make sure someone doesn't accidentally revert the fix. Ask yourself, is there anything in your PR that you feel it is important we not accidentally revert back to how it was before your fix?

Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing. If both you and the PR author believe this PR qualifies for a test exemption, escalate to the tech lead for the changed area to review and apply the test-exempt label. All reviewers should feel empowered to ask for tests before escalating.

Piinks

Thanks for addressing the review feedback and adding the widget test! This needs dart format run on examples/image_list/lib/main.dart and examples/image_list/test/widget_test.dart.

Piinks · 2026-10-28T18:46:33Z

+
+void main() {
+  testWidgets('MyHomePage disposes AnimationControllers properly', (WidgetTester tester) async {
+    HttpOverrides.global = _FakeHttpOverrides();


Nit: Consider resetting HttpOverrides.global in addTearDown so global state doesn't leak if additional tests are added to this file later

Nit: Consider resetting HttpOverrides.global in addTearDown so global state doesn't leak if additional tests are added to this file later

And done.
Thanks for the review!

Piinks

LGTM

- Moved AnimationController initialization to a late final variable to prevent redundant instantiation. - Added dispose() method to properly clean up the controllers. - Renamed images to imagesCount to conform to Dart naming conventions.

…ate naming.

…ir original identifiers.

…ist and fix lint warnings (type of local variable was non-obvious)

auto-submit · 2026-10-30T21:20:51Z

autosubmit label was removed for flutter/flutter/189526, because - The status or check suite Tree_analyze has failed. Please fix the issues identified (or deflake) before re-applying this label.

Piinks · 2026-10-30T21:26:57Z

@Okikday can you address the failing checks here?

Okikday · 2026-10-31T06:19:48Z

@Okikday can you address the failing checks here?

I have pushed a fix for the cross-import check (used widgets.dart instead of Material import and found the button by tooltip). So could you add the CICD label so CI re-runs? Thanks!

Okikday · 2026-10-31T10:54:59Z

Thanks for running the Tree analyzer workflow @AbdeMohlbi
I’ve formatted the widget test that was causing the failure. Could someone re-add the CICD label so CI re-runs?

Piinks

LGTM

auto-submit · 2026-11-02T22:04:15Z

autosubmit label was removed for flutter/flutter/189526, because This PR has not met approval requirements for merging. The PR author is not a member of flutter-hackers and needs 1 more review(s) in order to merge this PR.

Merge guidelines: A PR needs at least one approved review if the author is already part of flutter-hackers or two member reviews if the author is not a member of flutter-hackers before re-applying the autosubmit label. Reviewers: If you left a comment approving, please use the "approve" review action instead.

AbdeMohlbi · 2026-11-02T22:07:56Z

autosubmit label was removed for flutter/flutter/189526, because This PR has not met approval requirements for merging. The PR author is not a member of flutter-hackers and needs 1 more review(s) in order to merge this PR.

Merge guidelines: A PR needs at least one approved review if the author is already part of flutter-hackers or two member reviews if the author is not a member of flutter-hackers before re-applying the autosubmit label. Reviewers: If you left a comment approving, please use the "approve" review action instead.

yuh uh

This PR resolves a memory leak and cleans up naming conventions in the `image_list` Devicelab benchmark example. **What is changing:** - Moved the `AnimationController` instantiation out of the `build` method and into a `late final` variable to prevent redundant instantiation. - Added a `dispose()` method to properly clean up the controllers. **Why:** Previously, 50 new controllers were being instantiated on every `setState` trigger without ever being disposed, causing a memory leak. This refactor correctly manages the widget lifecycle while preserving the underlying performance benchmark (by appending `..repeat()` to the initialization so the UI thread remains appropriately stressed). *This PR fixes a trivial lifecycle and styling issue in a devicelab test script. No open issue is associated.* ## 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]. - [ ] I listed at least one issue that this PR fixes in the description above. - [ ] 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]. - [ ] I followed the [breaking change policy] and added [Data Driven Fixes] where supported. - [x] All existing and new tests are passing. [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/ [breaking change policy]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#handling-breaking-changes [Data Driven Fixes]: https://github.com/flutter/flutter/blob/main/docs/contributing/Data-driven-Fixes.md

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Okikday added 5 commits October 30, 2026 16:14

fix: Resolve memory leak in image_list example

91dfaa6

- Moved AnimationController initialization to a late final variable to prevent redundant instantiation. - Added dispose() method to properly clean up the controllers. - Renamed images to imagesCount to conform to Dart naming conventions.

refactor: move controllers initialization to initState and apply priv…

bcf48e0

…ate naming.

refactor: Reverted the previously modified variable names back to the…

f0265f4

…ir original identifiers.

test: add regression test for AnimationController disposal in image_l…

b1a5f29

…ist and fix lint warnings (type of local variable was non-obvious)

style: dart format and reset HttpOverrides in test

7da0f16

Piinks force-pushed the fix-image-list-leak branch from da63d9a to 7da0f16 Compare October 30, 2026 21:15

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Merge branch 'flutter:master' into fix-image-list-leak

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test: replace Material import to satisfy examples cross-import check

af4a9c8

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style: apply dart format to widget_test

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Roll Flutter from fcfb4f203eae to 934720261be0 (38 revisions) flutter/packages#13540

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Okikday commented Jul 15, 2026 •

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