Flutter ChangeNotifier Skill

This skill defines how to correctly use ChangeNotifier with the provider package for state management in Flutter.

1. Model

Extend ChangeNotifier to manage state. Keep internal state private and expose unmodifiable views. Call notifyListeners() on every state change.

class CartModel extends ChangeNotifier {
  final List<Item> _items = [];

  UnmodifiableListView<Item> get items => UnmodifiableListView(_items);

  void add(Item item) {
    _items.add(item);
    notifyListeners();