always_remove_listener

v0.4.0 Warning Resource Management

Flags addListener() calls in State lifecycle methods (initState, didUpdateWidget, didChangeDependencies) that do not have a matching removeListener() call in dispose(). Missing removal causes memory leaks when the Listenable outlives the widget.

Why use this rule

Every addListener() on a ChangeNotifier, ValueNotifier, or AnimationController creates a strong reference to the callback. If the listener is not removed in dispose(), the callback (and everything it captures) stays in memory even after the widget is unmounted. This rule ensures every add has a matching remove with the same target and callback.

See also: ChangeNotifier | removeListener

Don’t

class _BadState extends State<BadWidget> {
  final ValueNotifier<int> _counter = ValueNotifier(0);

  @override
  void initState() {
    super.initState();
    _counter.addListener(_onChanged); // No matching removeListener
  }

  void _onChanged() => setState(() {});

  @override
  Widget build(BuildContext context) => const SizedBox();
}

Do

class _GoodState extends State<GoodWidget> {
  final ValueNotifier<int> _counter = ValueNotifier(0);

  @override
  void initState() {
    super.initState();
    _counter.addListener(_onChanged);
  }

  @override
  void dispose() {
    _counter.removeListener(_onChanged);
    super.dispose();
  }

  void _onChanged() => setState(() {});

  @override
  Widget build(BuildContext context) => const SizedBox();
}

Configuration

To disable this rule:

plugins:
  many_lints:
    diagnostics:
      always_remove_listener: false