How to migrate from a StateNotifier with complex state to a new Notifier/AsyncNotifier

[abigotado]

Hello!

Need some help with migration to new version. Currently I'm using StateNotifier with complex state for operating with paginated lists. Also I use abstraction to reuse the same methods/states code. And I would like to migrate my code to new Notifiers with code generation. Could you please help me to understand, how I can do that?

Now I have a state for pagination:

part 'pagination_controller_state.freezed.dart';

/// State class for pagination screens.
@freezed
class PaginationControllerState<T> with _$PaginationControllerState<T> {
  /// Factory for generating PaginationControllerState.
  const factory PaginationControllerState({
    /// If true, data is loading.
    @Default(false) final bool isLoading,

    /// If true, error has occurred.
    @Default(false) final bool isError,

    /// Page of the list.
    final int? page,

    /// Error.
    final Object? error,

    /// List of items.
    final List<T>? items,

    /// Поиск по тексту.
    final String? search,

    /// Filter by status enum.
    @Default(EvaluationStatus.all) final EvaluationStatus filter,

    /// No more pages to load.
    @Default(false) final bool isEnd,
  }) = _PaginationControllerState<T>;
}

And I have a pagination controller abstraction:

import 'package:flutter/foundation.dart';
import 'package:hooks_riverpod/hooks_riverpod.dart';

/// Controller abstraction for pagination screens.
abstract class PaginationController<T>
    extends StateNotifier<PaginationControllerState<T>> {
  /// Creates a PaginationController.
  PaginationController() : super(PaginationControllerState<T>()) {
    fetchList();
  }

  /// Fetch list and manage states.
  Future<void> fetchList({
    final bool isRefresh = false,
    final bool isSocketUpdate = false,
    final String? search,
    final EvaluationStatus? filter,
  }) async {
    if (isSocketUpdate || isRefresh || !state.isEnd) {
      if (!state.isLoading) {
        state = state.copyWith(
          isLoading: !isSocketUpdate,
          isError: false,
          error: null,
          page: isRefresh ? null : state.page,
          items: isRefresh ? null : state.items,
          search: search ?? state.search,
          filter: filter ?? state.filter,
        );

        debugPrint('isSocketUpdate $isSocketUpdate');

        final int nextPage = (state.page ?? 0) + 1;
        try {
          final List<T>? list = await getList(
            isSocketUpdate ? 1 : nextPage,
            length: isSocketUpdate ? (state.page ?? 1) * 20 : null,
            isRefresh: isRefresh,
            search: state.search ?? '',
            filter: state.filter,
          );
          if (list != null) {
            state = state.copyWith(
              isEnd: list.length < 20,
              isLoading: false,
              items: <T>[
                if (!isSocketUpdate) ...state.items ?? <T>[],
                ...list,
              ],
              page: isSocketUpdate ? state.page : nextPage,
              search: search ?? state.search,
              filter: filter ?? state.filter,
            );
          }
        } catch (e) {
          debugPrint('ERROR in pagination controller: $e');
          state = state.copyWith(
            isLoading: false,
            isError: true,
            error: e.toErrorString(),
          );
        }
      }
    }
  }

  /// Load list from repository.
  Future<List<T>?> getList(
    final int page, {
    required final EvaluationStatus filter,
    final int? length,
    final bool isRefresh = false,
    final String? search,
  });
}

The abstraction has a preset method for operating with pagination and changing states. So it's only needed to override the method of getting the list and fix a type of list items. And I use these abstraction for several controllers, which handle states for different screens with paginated lists.

Here is an example:

/// Provider of [ParticipantsController].
final AutoDisposeStateNotifierProviderFamily<ParticipantsController,
        PaginationControllerState<AccessModel>, int>
    participantsControllerProvider = StateNotifierProvider.family.autoDispose<
        ParticipantsController, PaginationControllerState<AccessModel>, int>((
  final AutoDisposeStateNotifierProviderRef<ParticipantsController,
          PaginationControllerState<AccessModel>>
      ref,
  final int id,
) {
  return ParticipantsController(ref, id: id);
});

/// The controller of [EventScreen] states.
class ParticipantsController extends PaginationController<AccessModel> {
  /// Creates [ParticipantsController].
  ParticipantsController(this._ref, {required this.id});

  /// Provider Ref.
  final Ref _ref;

  /// Event id.
  final int id;

  @override
  Future<List<AccessModel>?> getList(
    final int page, {
    required final EvaluationStatus filter,
    final int? length,
    final bool isRefresh = false,
    final String? search,
  }) {
    debugPrint('event controller id: $id');
    return _ref.read(participantsRepositoryProvider(id)).fetchList(
          page,
          isRefresh: isRefresh,
          search: search,
          filter: filter,
          length: length,
        );
  }
}

I guess it is not possible to migrate this code to AsyncNotifier. Is it possible to use Notifier for this purpose instead?

[rrousselGit]

Hello!

It's kind of broad. Do you have a more specific question?
All StateNotifier usages should be possible to migrate to Notifier/AsyncNotifier.

[abigotado]

@rrousselGit Thank you for the answer!

Well, I'll try to specify.

1) Can I use Notifier the same way for abstraction and then generate providers for child classes?

Something like that:

abstract class PaginationController<T> extends Notifier<PaginationControllerState<T>> {...}`

and then:

@riverpod
class ParticipantsController extends PaginationController<AccessModel> {
@override
build() => AccessModel();
}

2) Is there a way to combine a complex state with AsyncNotifier?
in this example:

const factory PaginationControllerState({
    @Default(false) final bool isLoading,
    @Default(false) final bool isError,
    final int? page,
    final Object? error,
    final List<T>? items,
    final String? search,
    @Default(EvaluationStatus.all) final EvaluationStatus filter,
    @Default(false) final bool isEnd,
  }) = _PaginationControllerState<T>;

Is it possible to handle isLoading/isError with AsyncValue of AsyncNotifier but save all the other state arguments like page, filter, etc.?

[rrousselGit]

You can't make an abstract notifier. If you want to share logic, use a mixin instead

Is it possible to handle isLoading/isError with AsyncValue of AsyncNotifier but save all the other state arguments like page, filter, etc.?

Remove your isLoading/isError/error from the class and let AsyncValue deal with it. Your class would then only represent "data"

[abigotado]

You can't make an abstract notifier. If you want to share logic, use a mixin instead

Well, then I need to review all the logic of PaginationController as it was abstracting methods taken from StateNotifier class. I'm not sure, I'll be able to do something similar with mixin.

Remove your isLoading/isError/error from the class and let AsyncValue deal with it. Your class would then only represent "data"

Thank you, I'll try to do that.

[phamquoctrongnta]

@abigotado
On your build method of ParticipantsController, if you want to triggered a error so that what should you return?
Sorry for my English.

[abigotado]

@phamquoctrongnta Hi! It was just a schematic example, so build method just shows there's some logics inside. And, well, it's quite an old topic, I used Remy's advice and did what I needed with notifiers and mixins. And AsyncValue of course :) Worked perfectly