One BLoC per Screen

class ListBloc extends BaseBloc {
	// Streams the lists of items
  var _listOfItemsSubject = BehaviorSubject<List<Items>>();
  Stream<List<Items>> get listOfItemsStream => _listOfItemsSubject.stream;

	// Sink to fetch new data	
	var _fetchItemsSubject = PublishSubject<Event>();
  Sink<Event> get fetchItemsSink => _fetchItemsSubject.sink;

  ListBloc(ItemsManager manager) {
		// Every time we receive a fetch event, we fetch new items
    _fetchItemsSubject.stream
      .flatMap((_) => manager.fetchItems())
        .listen(_listOfItemsSubject.add, error: (e) => handleError(e));

		// When this BLoC is created, we want to have a list of items, so we fetch it
    _fetchItemsSubject.add(Event())
  }
}

class CategoryBloc extends BaseBloc {
	// Stream to stream the list, and Sink to add the list when the BLoC is created
  var _listOfItemsSubject = BehaviorSubject<List<Items>>();
  Sink<List<Items>> get listOfItemsSink => _listOfItemsSubject.sink;
  Stream<List<Items>> get listOfItemsStream => _listOfItemsSubject.stream;

  CategoryBloc() {
    // ...
  }
}

class AddBloc extends BaseBloc {
	// Sink to receive the event to add a new item
  var _addItemSubject = PublishSubject<Input>();
  Sink<Input> get addItemSink => _addItemSubject.sink; 
  
	// Stream with the response from the server, the new item
  var _addResponseSubject = PublishSubject<Item>();
  Stream<Item> get addResponseStream => _addResponseSubject.stream;
  
  AddBloc(ItemsManager manager) {
		// When we receive the new item event, send this item to our server
    _addItemSubject
        .stream
        .flatMap((input) => manager.addItem(input))
        .listen(_addResponseSubject.add, error: (e) => handleError(e));
  }
}

class EditBloc extends BaseBloc {
	// Sink to receive the event to edit an item
  var _editItemSubject = PublishSubject<Input>();
  Sink<Input> get editItemSink => _editItemSubject.sink; 
  
	// Stream with the response from the server, the edited item
  var _editResponseSubject = PublishSubject<Item>();
  Stream<Item> get editResponseStream => _editResponseSubject.stream;
  
  AddBloc(ItemsManager manager) {
		// When we receive the edit item event, send the edited item to our server
    _editItemSubject
        .stream
        .flatMap((input) => manager.editItem(input))
        .listen(_editResponseSubject.add, error: (e) => handleError(e));
  }
}