All 7 State Management with Riverpod questions
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What makes Riverpod genuinely different from Provider in terms of letting you properly read a given provider's own current value from essentially anywhere, entirely outside of the actual widget tree itself? How does ConsumerWidget let a StatelessWidget properly and reactively access and correctly rebuild in response to a given Riverpod provider's own current value? How do you properly handle loading, error, and data states when working with a FutureProvider or a StreamProvider in Riverpod, using the resulting AsyncValue's own convenient when method? How can you properly implement pull to refresh functionality that correctly triggers a Riverpod provider to actually genuinely refetch its own underlying data using the ref.refresh or invalidate methods? How do you properly implement optimistic updates using Riverpod, immediately updating your interface before an actual backend confirmation genuinely arrives, then properly rolling back that particular change if the request genuinely happens to fail? How should a large team properly organize their overall Riverpod provider architecture, deciding exactly how granular each individual given provider should genuinely be and how they should genuinely be organized across an entire large codebase?
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How does StateNotifierProvider let you properly manage genuinely more complex state that requires several genuinely separate distinct methods for updating it, compared to the considerably simpler StateProvider?

Intermediate

Answer

StateNotifierProvider works together with a StateNotifier subclass, letting you properly define several genuinely separate distinct named methods for updating that particular provider's own held state, such as addItem and removeItem on a genuine shopping cart, rather than the considerably simpler StateProvider, which is generally genuinely best suited for a fairly simple piece of state that only ever genuinely needs to be directly and simply reassigned, and this particular pattern provides a genuinely clean, well organized location specifically for containing genuinely more complex business logic related to updating that particular given piece of state.
class CartNotifier extends StateNotifier<List<String>> {
  CartNotifier() : super([]);
  void addItem(String item) => state = [...state, item];
}

final cartProvider = StateNotifierProvider<CartNotifier, List<String>>((ref) => CartNotifier());
Real-world example A shopping cart feature uses StateNotifierProvider together with a dedicated CartNotifier class exposing genuinely clear, well named addItem and removeItem methods, keeping that particular cart's own update logic properly organized and cleanly separate from the actual widget code itself.

Common follow-ups: How does StateNotifierProvider genuinely compare to the considerably newer code generation based Notifier class?;What genuinely happens if you try to directly mutate a StateNotifier's own held state without properly going through one of its own defined methods?

Flutter Riverpod Code Generation & Providers;Dart Collections & Generics
All 7 State Management with Riverpod questions