provider_extension.dart

import 'package:provider/provider.dart';

extension ProviderStoreBuildContextX on BuildContext {
  /// Read the store once, doesn't subscribe a BuildContext to update.
  AppStore readStore() => read<AppStore>();

  /// Watch the store by subscribing to a BuildContext.
  AppStore watchStore() => watch<AppStore>();

  /// Select a piece of the store, subscribing a BuildContext to update only
  /// when the underlying field changes. Uses `==` operator to determine changes
  T selectField<T>(T Function(AppStore s) selector) => select(selector);
}

store_architecture.dart

import 'package:flutter/foundation.dart';

/// A [ChangeNotifier] with built in fields for [initState], [initialized] and [setState].
///
/// Contains multiple [ChildStore]s
abstract class Store extends ChangeNotifier {
  /// Initialize this store.
  ///
  /// Must call super after initialization is complete.
  @mustCallSuper
  Future<void> initState() async {
    _initialized = true;
    notifyListeners();
  }

  /// If this [ChildStore] is fully initialized
  bool get initialized => _initialized;
  bool _initialized = false;

  /// Alternative to notifyListeners. Matches [StatefulWidget] semantics.
  void setState(Function fn) {
    fn();
    notifyListeners();
  }
}

/// A [ChangeNotifier] with built in fields for [RootStore], [initState],
/// [initialized] and [setState].
abstract class ChildStore<T extends Store> extends Store {
  ChildStore(this.store);

  /// The parent store that contains this store.
  final T store;
}

/// A [Store] that has a [registerStores]
/// method which connects these child stores to this [RootStore],
/// initializes them and then disposes of the subscription.
abstract class RootStore extends Store {
  List<Store> _children = [];

  /// Register stores with this [RootStore].
  ///
  /// The root store will subscribe to all childrens
  /// [notifyListeners] calls, initialize them, and dispose
  /// of the subscription.
  void registerChildren(List<Store> children) {
    _children = children;
  }

  @override
  Future<void> initState() async {
    if (_children.isEmpty) {
      debugPrint(
        "WARNING: $this has no _children. Typically a RootStore would have _children stores.",
      );
    }

    /// Connect the root store's [notifyListeners] method to
    /// all child stores [notifyListeners] method.
    for (var e in _children) {
      e.addListener(notifyListeners);
    }

    /// Await all child store's [initState]
    await Future.wait(_children.map((e) => e.initState()));

    return super.initState();
  }

  @override
  void dispose() {
    /// Dispose all [notifyListeners] handlers.
    for (var e in _children) {
      e.removeListener(notifyListeners);
      e.dispose();
    }

    super.dispose();
  }
}