Custom flutter state management by wrapping 3rd party state management libraries

state-management.dart

import 'package:flutter/widgets.dart';
import 'package:flutter_bloc/flutter_bloc.dart';

// this is an interface to a state management library
// clients of this library should not depend on any specific state management library
class Published<T> {
  final _CubitWrapper<T> _cubit;

  Published(T val) : _cubit = _CubitWrapper(val);

  T get val => _cubit.state;
  set val(T newVal) => _cubit.update(newVal);

  Future<void> close() => _cubit.close();
}

// this class is needed because Cubit.emit() is @protected
class _CubitWrapper<T> extends Cubit<T> {
  _CubitWrapper(T state) : super(state);

  void update(T newVal) => emit(newVal);

  @override
  Future<void> close() async {
    print("Closing cubit, state=$state");
    return super.close();
  }
}

class PublishedConsumer<T> extends BlocConsumer<_CubitWrapper<T>, T> {
  PublishedConsumer._({
    required Published<T> published,
    required Widget Function(BuildContext, T) builder,
    required void Function(BuildContext, T) listener,
  }) : super(bloc: published._cubit, builder: builder, listener: listener);

  factory PublishedConsumer.withContext({
    required Published<T> published,
    Widget Function(BuildContext, T)? builder,
    void Function(BuildContext, T)? listener,
  }) {
    return PublishedConsumer._(
      published: published,
      builder: builder ?? (_, __) => Container(),
      listener: listener ?? (_, __) => null,
    );
  }

  factory PublishedConsumer.new({
    required Published<T> published,
    Widget Function(T)? builder,
    void Function(T)? listener,
  }) {
    return PublishedConsumer._(
      published: published,
      builder: builder == null ? (_, __) => Container() : (_, v) => builder(v),
      listener: listener == null ? (_, __) => null : (_, v) => listener(v),
    );
  }
}

// sample implementation

class LibraryScreen extends View<LibraryPage> {
  LibraryScreen() : super(LibraryPage());

  LibraryPage get page => viewModel;

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        ChipWheel(LibraryChips.values, onSelect: page.chipTapped),
        Expanded(
          child: PublishedConsumer(
            published: page.chip,
            builder: (_) => Text(page.chip.name),
          ),
        ),
      ],
    );
  }
}

class LibraryPage extends ViewModel {
  final chip = Published(LibraryChips.all);

  LibraryPage();

  void chipTapped(LibraryChips chip) => this.chip.val = chip;
}