store.dart

// ignore_for_file: public_member_api_docs
import 'package:flutter/foundation.dart';
import 'package:flutter/widgets.dart';
import 'package:provider/provider.dart';
import 'package:provider/single_child_widget.dart';

/// A provider that exposes a [ValueNotifier] in two independent pieces.
///
/// [StoreProvider] will expose both [ValueNotifier] and [ValueNotifier.value] independently
/// to its dependents.
///
/// For the [ValueNotifier]:
///
/// ```dart
/// class MyStore extends ValueNotifier<int> {
///   MyStore(): super(0);
/// }
/// ```
///
/// it is possible to obtain the `MyStore` instance through:
///
/// ```dart
/// context.watch<MyStore>(context);
/// ```
///
/// and the current value through:
///
/// ```dart
/// context.watch<int>(context);
/// ```
class StoreProvider<Value, Controller extends ValueNotifier<Value>> extends SingleChildStatelessWidget {
  /// Allows to specify parameters to [StoreProvider].
  StoreProvider({
    Key key,
    @required this.create,
    Widget child,
  }) : super(key: key, child: child);

  final Create<Controller> create;

  @override
  Widget buildWithChild(BuildContext context, Widget child) {
    return InheritedProvider<Controller>(
      create: create,
      builder: (context, _) {
        return ValueListenableProvider<Value>.value(
          value: context.watch<Controller>(),
          child: child,
        );
      },
    );
  }
}

store_example.dart

import 'package:flutter/widgets.dart';

enum _Action {
  increment,
  decrement,
}

class MyStore extends ValueNotifier<int> {
  MyStore() : super(0);

  void increment() => value++;

  void decrement() => value--;
}

class Bar {}

class Initial implements Bar {}

class Loading implements Bar {}

class Error implements Bar {
  Error(this.err);

  final Object err;
}

class Loaded implements Bar {
  Loaded(this.value);

  final int value;
}

class Foo extends ValueNotifier<Bar> {
  Foo() : super(Initial());

  Future<void> fetch() async {
    value = Loading();
    try {
      final result = await Future<int>.delayed(Duration(seconds: 1));
      value = Loaded(result);
    } catch (err) {
      value = Error(err);
    }
  }
}

看不懂

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