Common Bloc

class CommonBloc extends BaseBloc {
  var _listOfItemsSubject = BehaviorSubject<List<Items>>();
  Stream<List<Items>> get listOfItemsStream => _listOfItemsSubject.stream;

	var _fetchItemsSubject = PublishSubject<Event>();
  Sink<Event> get fetchItemsSink => _fetchItemsSubject.sink;

  CommonBloc(ItemsManager manager) {
    _fetchItemsSubject.stream
      .flatMap((_) => manager.fetchItems())
        .listen(_listOfItemsSubject.add, error: (e) => handleError(e));

    _fetchItemsSubject.add(Event())
  }
}

class ListBloc extends BaseBloc {
  
  ListBloc() {
    //...
  }
}

class CategoryBloc extends BaseBloc {

  CategoryBloc() {
    // ...
  }
}

class AddBloc extends BaseBloc {
  var _addItemSubject = PublishSubject<Input>();
  Sink<Input> get addItemSink => _addItemSubject.sink;
  
  var _addResponseSubject = PublishSubject<Item>();
  Stream<Item> get addResponseStream => _addResponseSubject.stream;
  
  AddBloc(ItemsManager manager) {
    _addItemSubject
        .stream
        .flatMap((input) => manager.addItem(input))
        .listen(_addResponseSubject.add, error: (e) => handleError(e));
  }
}

class EditBloc extends BaseBloc {
  var _editItemSubject = PublishSubject<Input>();
  Sink<Input> get editItemSink => _editItemSubject.sink;
  
  var _editResponseSubject = PublishSubject<Item>();
  Stream<Item> get editResponseStream => _editResponseSubject.stream;
  
  AddBloc(ItemsManager manager) {
    _editItemSubject
        .stream
        .flatMap((input) => manager.editItem(input))
        .listen(_editResponseSubject.add, error: (e) => handleError(e));
  }
}