响应式仓库

一个监听来自仓库层的Stream（而不是显式使用get/fetch）的例子，作为BLoC到BLoC通信的解决方案，灵感来自bloc library的更新文档和这条推文。

请查看Medium文章，其中更详细地解释了所有内容

示例

主要要注意的是，当DetailsCubit成功切换isFavorite时，ListCubit如何重新加载（并按收藏排序）ItemsScreen，但DetailsCubit没有对ListCubit的引用。

example

BLoC

class ListCubit extends Cubit<ListState> {
  ListCubit()
      : _itemsRepository = getIt.get(),
        _sorter = Sorter(),
        super(ListLoading()) {
    _subscribe();
  }

  final ItemsRepository _itemsRepository;
  final Sorter _sorter;
  late final StreamSubscription _subscription;

  void load({bool force = false}) async {
    emit(ListLoading());
    await _itemsRepository.fetchAll(force: force);
  }

  void reload() => load(force: true);

  void _subscribe() {
    _subscription = _itemsRepository.items.listen(
      (items) {
        final sortedItems = _sorter.sortByFavorite(items);
        emit(ListLoaded(sortedItems));
      },
      onError: (error) => emit(ListError('$error')),
    );
  }

  @override
  Future<void> close() {
    _subscription.cancel();
    return super.close();
  }
}

class DetailsCubit extends Cubit<DetailsState> {
  DetailsCubit()
      : _itemsRepository = getIt.get(),
        super(const DetailsLoading());

  final ItemsRepository _itemsRepository;
  Item? _currentItem;

  void load(int? itemId) async {
    emit(DetailsLoading(_currentItem));

    if (itemId == null) {
      emit(const DetailsError('Cannot parse itemId'));
      return;
    }

    try {
      _currentItem = await _itemsRepository.getOne(itemId);
      if (_currentItem != null) {
        emit(DetailsLoaded(_currentItem!));
      } else {
        emit(DetailsError('Cannot find item $itemId'));
      }
    } catch (e, st) {
      emit(DetailsError('$e: $st'));
    }
  }

  void toggleFavorite(int itemId) async {
    emit(DetailsLoading(_currentItem));

    _currentItem = await _itemsRepository.toggleFavorite(itemId);

    if (_currentItem != null) {
      emit(DetailsLoaded(_currentItem!));
    } else {
      emit(const DetailsError('Failed to toggle favorite'));
    }
  }
}

Repository

abstract class ItemsRepository {
  final _controller = StreamController<List<Item>>();

  Stream<List<Item>> get items => _controller.stream;

  void addToStream(List<Item> items) => _controller.sink.add(items);

  Future<void> fetchAll({bool force = false});
  Future<Item?> getOne(int itemId);
  Future<Item?> toggleFavorite(int itemId);
}

class FakeItemsRepository extends ItemsRepository {
  List<Item> _currentItems = [];

  @override
  Future<void> fetchAll({bool force = false}) async {
    if (_currentItems.isEmpty || force) {
      await Future.delayed(const Duration(milliseconds: 400));
      _currentItems = List.generate(12, (_) => Item.fake());
    }

    addToStream(_currentItems);
  }

  @override
  Future<Item?> getOne(int itemId) async {
    if (_currentItems.isEmpty) {
      await fetchAll();
    }

    try {
      return _currentItems.firstWhere((item) => item.id == itemId);
    } catch (e) {
      return null;
    }
  }

  @override
  Future<Item?> toggleFavorite(int itemId) async {
    await Future.delayed(const Duration(milliseconds: 200));

    final item = await getOne(itemId);
    if (item == null) {
      return null;
    }

    final toggledItem = item.copyWith(isFavorite: !item.isFavorite);
    _updateCurrentItemsWith(toggledItem);

    addToStream(_currentItems);

    return toggledItem;
  }

  void _updateCurrentItemsWith(Item item) {
    final index = _currentItems.indexWhere((it) => it.id == item.id);
    if (index != -1) {
      _currentItems[index] = item;
    }
  }
}

GitHub

查看 Github