<StatefulWidget> --- <State>・・・状態管理
                        ↑
                  <ChildWidget>
                        ↑
                  <AncestorWidget>・・・setState()

-------------------------------------------------
<StatefulWidget> --- <State>・・・状態管理
       ↑                ↑
  this.child       widget.child・・・setState()

// Widgetはいつ何時でも状態を持たない
class MyWidget extends StatefulWidget {
  const MyWidget({Key? key}) : super(key: key);

  @override
  State<MyWidget> createState() => _MyState();
}

// Stateオブジェクトが状態を持つ
class _MyState extends State<MyWidget> {
  // ユーザーが入力した文字列(状態)
  var inputText = '';

  @override
  Widget build(BuildContext context) {
    run MaterialApp(
        ...
    );
  }
}

// 以下, ...のどこか

// 状態変化
TextField(
  onChanged: (text) {
    // 入力内容が変化するたびに呼び出される
    inputText = text;
  }
),

~~

// 状態更新
setState(() => {

});

   <StatefulWidget> ---- <State>・・・状態管理
                            ↑ dependOnInheritedWidgetOfExactType() / getElementForInheritedWidgetOfExactType()
                    <InheritedWidget>
                       ↑         ↑
                     <UI_A>.     |
                                 |
                               <UI_*>

// StatefulWidgetクラスにInheritedWidgetクラス経由でStateクラスを参照する関数of()を実装する
e.g.
class MyStatefulWidget extends StatefulWidget {
  MyStatefulWidget({
    Key? key, 
    this.child,
  }) : super(key: key);

  @override
  MyState createState() => MyState();

  static MyState of(BuildContext context, {bool rebuild = true}) {
    if (rebuild) {
      MyInheritedwidget? inheritedWid = context.dependOnInheritedWidgetOfExactType<MyInheritedWidget>();
      return inheritedWid!.data;
    }

    // リビルドされない
    InheritedElement? inheritedElem = const.getElementForInheritedWidgetOfExactType<MyInheritedWidget>();
    MyInheritedWidget inheritedWid = inheritedElem!.widget as MyInheritedWidget;
    return inheritedWid.data;

// MyStatefulWidget
static MyState of(BuildContext context, String aspect) {
  return InheritedModel.inheritFrom<MyInheritedWidget>(context, aspect: aspect)!.data;

// Process (Interface)
class CountRepository {
  Future<int> fetch() {
    return Future.delayed(const Duration(seconds: 1)).then((_) {
      return 1;
    });
  }
}

// BLoC
class CounterBloc {
  final CountRepository _repository;
  final _valueController = StreamController<int>();
  final _loadingController = StreamController<bool>();
  Stream<int> get value => _valueController.stream;
  Stream<bool> get isLoading => _loadingController.stream;
  int _counter = 0;

  CounterBloc(this._repository) {
    _valueController.sink.add(_counter);
    _loadingController.sink.add(false);
  }

  void incrementCounter() async {
    _loadingController.sink.add(true);
    var increaseCount = await _repository.fetch().whenComplete(() {
      _loadingController.sink.add(false);
    });
    _counter += increaseCount;
    _valueController.sink.add(_counter);
  }

  void dispose() {
    _valueController.close();
    _loadingController.close();
  }
}

~~~

// Blocクラスの初期化
@override
void initState() {
  super.initState();
  counterBloc = CounterBloc(CountRepository());
}

~~

// StreamBuilderの利用@受信側UI
@override
Widget build(BuildContext context) {
  return StreamBuilder<int>(
    //initialData: 0,
    stream: counterBloc.value, // Stream<int>
    builder: (BuildContext context, AsyncSnapshot<int> snapshot) {
      return Text(
        "${snapshot.data}",
        style: Theme.of(context).textTheme.displayMedium,
      );
    }
  );
}

~~
// BLoCの更新メソッドの利用@送信側UI
return ElevatedButton(
  onPress:() {
    counterBloc.incrementCounter();
  },
  child: const Icon(Icons.add),
)

    <StatefulWidget> ----- <State>
        ↑ |- <Repo>           |- <BLoC>
        | |- child            |- widget.child
        | |- of()             |- widget.repo
        |
    <InheritedWidget>
     |             ↑
     ↓ 受信         | 送信
    <UI_A>        <UI_B>