Minimal implementation of InheritedWidget

inherited_widget.dart

import 'package:flutter/material.dart';

void main() => runApp(
      StateWrapper(
        MaterialApp(
          home: Scaffold(
            body: App(),
            ),
        ),
      ),
    );

class App extends StatelessWidget {
  @override
  Widget build(BuildContext ctx) {
    final state = InheritedState.of(ctx);
    return Column(children: <Widget>[
      Text('You pressed the button ${state.x} times.'),
      TextButton(
        onPressed: () {
          state.updateX(state.x + 1);
        },
        child: const Icon(Icons.add),
      ),
    ]);
  }
}

class StateWrapper extends StatefulWidget {
  const StateWrapper(this.child, {super.key});

  @override
  State<StateWrapper> createState() => _WrapperState();

  final Widget child;
}

class _WrapperState extends State<StateWrapper> {
  int x = 0;

  @override
  Widget build(BuildContext _) => InheritedState(
    x,
    (int nextX) => setState(() => x = nextX),
    child: widget.child,
  );
}

class InheritedState extends InheritedWidget {
  const InheritedState(this.x, this.updateX, {super.key, required super.child});

  final int x;
  final void Function(int) updateX;

  @override
  bool updateShouldNotify(InheritedState old) => x != old.x;

  static InheritedState of(BuildContext ctx) {
    return ctx.dependOnInheritedWidgetOfExactType<InheritedState>()!;
  }
}