avoid_state_constructors

v0.4.0 Warning State Management

Flags State subclasses that have constructors with non-empty bodies or initializer lists. Initialization logic in State classes should live in initState(), not in the constructor, to respect the Flutter widget lifecycle.

Why use this rule

The State constructor runs before the framework has fully initialized the state object. At construction time, widget, context, and other framework-provided properties are not yet available. Placing logic in the constructor can lead to subtle bugs when that logic depends on the widget tree. Using initState() ensures all framework wiring is in place.

See also: State class | State.initState

Don’t

class _BadWidget1State extends State<BadWidget1> {
  late String _data;

  // Constructor body should be empty — move logic to initState()
  _BadWidget1State() {
    _data = 'Hello';
  }

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

class _BadWidget2State extends State<BadWidget2> {
  final String _data;

  // Initializer list in State constructor — move logic to initState()
  _BadWidget2State() : _data = 'Hello';

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

Do

class _GoodWidgetState extends State<GoodWidget> {
  late String _data;

  @override
  void initState() {
    super.initState();
    _data = 'Hello';
  }

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

// Empty constructor is fine
class _GoodWidget2State extends State<GoodWidget2> {
  _GoodWidget2State();

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

Configuration

To disable this rule:

plugins:
  many_lints:
    diagnostics:
      avoid_state_constructors: false