flutter riverpod: initialize state on notify provider

Question

I am using notifier provider like this :

@riverpod
class MainProductNew extends _$MainProductNew {
  @override
  AsyncValue<MainProductStateModel> build(String id) {
    return const AsyncValue.loading();
  }

  Future<void> getMainProduct() async {
    final result = await ref.watch(productViewNewRepositoryProvider).getMainProduct(id);

    state = AsyncValue.data(state.value!.copyWith(mainProductModel: result.extractDataOrThrow));
  }
}

When I am calling getMainProduct method and I want to update the state , since state value is null I get :

Error: Unexpected null value.

the issue is here :

state.value!.copyWith

MainProductStateModel is a freezed class, How can I correctly initialize the state?

Do I need to create an object if the state is null but after that I can use copywith, Is it correct ?

Answer 1

In general, if your state shoudl be AsyncLoading until a known future completes, return that future. So your code should look like this:

@riverpod
class MainProductNew extends _$MainProductNew {
  @override
  Future<MainProductStateModel> build(String id) {
    return _getMainProduct();
  }

  Future<MainProductStateModel> _getMainProduct() async {
    final result = await ref.watch(productViewNewRepositoryProvider).getMainProduct(id);

    return result;
  }
}

I made it private to distinguish between internal functions and external mutation API methods. And you could further simplify that internal function as:

  Future<MainProductStateModel> _getMainProduct() =>
    ref.watch(productViewNewRepositoryProvider).getMainProduct(id);