Flutter Dispose Discipline

Flutter Dispose Discipline Skill

Every resource that requires cleanup MUST be disposed. No exceptions.

When to apply

• Creating a StatefulWidget with any controller
• Code review of StatefulWidget code
• Memory leak investigation
• User reports "my app gets slower over time"

Resources that MUST be disposed

Correct pattern

class MyWidget extends StatefulWidget { ... }

class _MyWidgetState extends State<MyWidget> {
  late final TextEditingController _nameController;
  late final ScrollController _scrollController;
  StreamSubscription<Event>? _subscription;

  @override
  void initState() {
    super.initState();
    _nameController = TextEditingController();
    _scrollController = ScrollController();
    _subscription = eventStream.listen(_onEvent);
  }

  @override
  void dispose() {
    _subscription?.cancel();
    _scrollController.dispose();
    _nameController.dispose();
    super.dispose();  // ALWAYS last
  }
}

Common mistakes

Forgetting dispose

// BAD — controller leaks
class _State extends State<MyWidget> {
  final controller = TextEditingController();
  // NO dispose() override!
}

Disposing in wrong order

// BAD — super.dispose() called first
@override
void dispose() {
  super.dispose();  // WRONG — should be last
  _controller.dispose();
}

Using controller after dispose

// BAD — accessing controller in async callback after dispose
Future<void> _save() async {
  await repository.save(_controller.text); // might be disposed
  // FIX: check mounted before accessing controller
  if (!mounted) return;
  _controller.clear();
}

Flutter Hooks alternative

With flutter_hooks, disposal is automatic:

class MyWidget extends HookWidget {
  @override
  Widget build(BuildContext context) {
    final controller = useTextEditingController(); // auto-disposed
    final scrollController = useScrollController(); // auto-disposed
    // ...
  }
}

Checklist

• Every controller has a matching dispose() call
• Every StreamSubscription has cancel() in dispose()
• super.dispose() is the LAST call in dispose()
• No controller access after potential dispose (async gaps)
• Timer instances are cancelled in dispose()
• AnimationController uses vsync: this with TickerProviderStateMixin

Source: thawzintoe-ptut/Ptut-claude — distributed by TomeVault.