Minimal example demonstrating Flutter InheritedWidgets with mutable state

main.dart

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      home: MyWidget(),
    );
  }
}

class MyWidget extends StatefulWidget {
  const MyWidget({super.key});

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

class _MyWidgetState extends State<MyWidget> {
  int c = 0;

  void increment() {
    setState(() {
      c++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Count(c: c, increment: increment, child: const NestedWidget());
  }
}

class Count extends InheritedWidget {
  const Count({
    super.key,
    required this.c,
    required this.increment,
    required super.child,
  });

  final int c;
  final void Function() increment;

  static Count of(BuildContext context) =>
      context.dependOnInheritedWidgetOfExactType<Count>()!;

  @override
  bool updateShouldNotify(Count old) => c != old.c;
}

class NestedWidget extends StatelessWidget {
  const NestedWidget({super.key});

  @override
  Widget build(BuildContext context) {
    final c = Count.of(context).c;
    return TextButton(
      onPressed: Count.of(context).increment,
      child: Text('$c', textScaleFactor: 3),
    );
  }
}