StateNotifier using either Ref or WidgetRef

[scopendo]

This discussion is about having a state notifier that wants to read values held by other providers, using either the Ref passed to a provider's create function or the WidgetRef of a ConsumerWidget. The reason is that sometimes the (generic) state notifier is instantiated via the provider create function and sometimes it is set via a ProviderScope override.

The problem encountered is that Ref and WidgetRef do not appear to implement a common interface. I got around this by passing the Reader method to the state notifier instead.

abstract class AppController<State> extends StateNotifier<State> {
  AppController(this.read, State initialState) : super(initialState);

  final Reader read;
}

However, I wondered why Ref and WidgetRef don't share a common interface? It's possible that a state notifier might also want to listen to or refresh other providers.

[rrousselGit]

However, I wondered why Ref and WidgetRef don't share a common interface?

That's voluntary. The fact that you need a common interface shows a flaw in your architecture

You most definitely did something wrong somewhere. You should never need to use WidgetRef outside of widgets

[rrousselGit]

In particular, you should look into Inversion of Control.

Chances are there's a way to refactor the code path currently using WidgetRef and extract that logic into a provider instead, therefore using Ref.

[scopendo]

I'm happy to accept that but at the moment the only way I see around it is to pass the dependencies in when overriding the provider's value on the provider scope, rather than using a ref internally.

Suppose that we have a list of "categories" and that tapping on one of them opens the category screen, with the selected or "current" category being set on a ProviderScope, but not as a simple state value but rather wrapped in a StateNotifier so that we can perform "someAction" on the category screen that changes the current category state.

class _CategoryListTile extends ConsumerWidget {
  const _CategoryListTile({required this.category});

  final CategoryData category;

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    return ListTile(
      title: Text(category.name),
      onTap: () => Navigator.push(
        context,
        MaterialPageRoute<void>(
          builder: (_) => ProviderScope(
            overrides: [
              currentCategoryProvider.overrideWithValue(
                CategoryController(ref.read, category), // <-- where I was seemingly doing the wrong thing
              ),
            ],
            child: const CategoryScreen(),
          ),
        ),
      ),
    );
  }
}

final currentCategoryProvider = StateNotifierProvider<CategoryController, CategoryData>(
  (_) => throw 'Provider value must be overridden',
);

class CategoryController extends StateNotifier<CategoryData> {
  CategoryController(this.read, CategoryData category) : super(category);

  final Reader read;

  Future<void> someAction() async {
    final dependency1 = read(dependency1Provider);
    final dependency2 = read(dependency2Provider);
    ...
    state = state.copyWith(...);
   }
}

In this scenario, I don't think I'm misusing Riverpod by accessing the dependencies internally, rather than passing them in. I also don't see how this CategoryController could source its reader function from anywhere but a WidgetRef given that the category controller value is set directly on the ProviderScope via an override.

[rrousselGit]

Try using overrideWithProvider insted of overrideWithValue

currentCategoryProvider.overrideWithProvider(
  StateNotifierProvider((ref) => CategoryController(ref, category),
)

[scopendo]

Perfect.