main.dart

// ignore_for_file: avoid_print

import 'package:flutter/material.dart';

void main() {
  runApp(const RootWidget());
}

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

  @override
  State<RootWidget> createState() => _RootWidgetState();
}

class _RootWidgetState extends State<RootWidget> {
  @override
  Widget build(BuildContext context) {
    AppState mainState = AppState()
      ..first = "Initial value set on instantiation in main.dart";
    return SuperState(
      state: mainState,
      child: MaterialApp(
        title: 'State maintenance demo',
        theme: ThemeData(
          colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
          useMaterial3: true,
        ),
        home: const A(),
      ),
    );
  }
}

class AppState {
  String first = "";
}

class SuperState extends StatefulWidget {
  final AppState state;
  final Widget child;
  const SuperState({super.key, required this.state, required this.child});

  @override
  State<SuperState> createState() => SuperStateState();

  // static SuperStateState of(BuildContext context) {
  //   var foo = context.findAncestorStateOfType<SuperStateState>();
  //   assert(foo != null, "Wait, how can the State be null?");
  //   return foo!;
  // }
}

class SuperStateState extends State<SuperState> {
  late AppState _state;

  @override
  void initState() {
    _state = widget.state;
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return SuperStateInheritedWidget(
      state: _state,
      update: update,
      child: widget.child,
    );
  }

  void update(AppState newState) {
    print("SuperState setState: ${widget.state.first} => ${newState.first}");
    setState(() {
      _state = newState;
    });
  }

  AppState getState() {
    return widget.state;
  }
}

class SuperStateInheritedWidget extends InheritedWidget {
  final AppState state;
  final void Function(AppState) update;
  const SuperStateInheritedWidget(
      {super.key,
      required this.state,
      required this.update,
      required super.child});

  static SuperStateInheritedWidget of(BuildContext context) {
    return context.getInheritedWidgetOfExactType<SuperStateInheritedWidget>()!;
  }

  @override
  bool updateShouldNotify(covariant SuperStateInheritedWidget oldWidget) {
    return true;
  }
}

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

  @override
  State<A> createState() => _AState();
}

class _AState extends State<A> {
  AppState? state;

  String first = "";
  final TextEditingController _controller = TextEditingController();

  @override
  Widget build(BuildContext context) {
    var sss = SuperStateInheritedWidget.of(context);
    state = sss.state;
    first = state!.first;
    _controller.text = first;
    print("A builder is running. first is '${state!.first}'");

    return Scaffold(
      body: Center(
        child: Column(
          children: [
            Text("A $first"),
            TextField(
              onChanged: (val) => first = val,
              decoration: const InputDecoration(
                labelText: "First name",
              ),
              controller: _controller,
            ),
            const A1(),
          ],
        ),
      ),
    );
  }
}

class A1 extends StatefulWidget {
  const A1({super.key});

  @override
  State<A1> createState() => _A1State();
}

class _A1State extends State<A1> {
  AppState? state;
  String first = "";
  final TextEditingController _controller = TextEditingController();
  @override
  void didChangeDependencies() {
    print("A1 dcd is running");
    super.didChangeDependencies();
  }

  @override
  Widget build(BuildContext context) {
    state = SuperStateInheritedWidget.of(context).state;

    print("A1 builder is running. First is ${state!.first}");
    first = state!.first;
    _controller.text = first;
    return Center(
      child: Column(
        children: [
          Text("A1 $first"),
          TextField(
            onChanged: (val) => first = val,
            decoration: const InputDecoration(
              labelText: "First name",
            ),
            controller: _controller,
          ),
          TextButton(
            onPressed: () => SuperStateInheritedWidget.of(context)
                .update(AppState()..first = "Set in A1 btn click"),
            child: const Text("Update"),
          ),
        ],
      ),
    );
  }
}