Improved a Flutter diagnostic message.

I build with Flutter, and "setState() called after dispose()" is an assertion nearly every Flutter developer runs into eventually. The framework already explained two ways to trigger it — a timer or an animation callback — but not the way I saw it happen most often in real apps: an async gap. I opened a small PR to the Flutter framework to close that gap in the error message itself.

The assertion in State.setState() said the error "can occur when code calls setState() from a timer or an animation callback." In practice the most common trigger is different: you await a network request or a Future inside a State, the user navigates away so the widget is disposed, then the await resolves and its callback calls setState() on a State that no longer has a place in the tree. Because the message never mentioned asynchronous gaps, developers hitting it through async code often did not recognise their own bug.

• 01Expanded the ErrorDescription in State.setState()’s "called after dispose" assertion (packages/flutter/lib/src/widgets/framework.dart) to add asynchronous operations — an awaited network request or other Future completing after the widget has been removed from the tree — alongside the existing timer and animation-callback causes.
• 02Added a widget test (packages/flutter/test/widgets/framework_test.dart) that removes a StatefulBuilder from the tree, calls setState() on the now-defunct State, and asserts the thrown FlutterError message explains the asynchronous cause.
• 03Net change: 2 files, +34 / −1.

-'This error can occur when code calls '
-'setState() from a timer or an animation callback.',

+'This error can occur when code calls '
+'setState() from a timer, from an animation callback, or after an '
+'asynchronous operation (such as an awaited network request or other '
+'Future) completes after the widget has been removed from the tree.',

I opened the pull request against Flutter’s master branch and signed the contributor licence agreement. Two members of the Flutter team reviewed it; I addressed their feedback over a couple of iterations, and once it was approved and the required CI checks passed, it was merged.

Once the approvals and required checks were in place, the PR was merged into flutter/flutter on July 7, 2026 by the project’s auto-submit bot (merge commit 8580e15).

framework.dart ships with Flutter, so the message reaches anyone who hits this error. The next time someone triggers "setState() called after dispose()" from an async callback, the text now points at the likely cause instead of leaving them guessing. It is a small change to a diagnostic message that Flutter developers read when something breaks.

• ▹A clearer error message is a real, mergeable contribution — you do not have to touch the engine to help the next person who hits the same assertion.
• ▹Match a repository’s conventions exactly: sign the CLA, use the real PR template, and add a test even for a message-only change.
• ▹Respond to review feedback quickly and precisely — small, well-aimed revisions are what keep a PR moving toward merge.