Example of ValueNotifier & ValueListenerBuilder to replace Rx from Getx.

main.dart

import 'package:flutter/material.dart';

///
/// @see https://api.flutter.dev/flutter/widgets/ValueListenableBuilder-class.html
/// @see https://api.flutter.dev/flutter/foundation/ValueNotifier-class.html
///
ValueNotifier<int> counter = ValueNotifier<int>(0);

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

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        appBar: AppBar(
          title: const Text('ValueNotifier<T>() sample'),
        ),
        body: ValueListenableBuilder<int>(
            valueListenable: counter,
            builder: (BuildContext context, int value, child) {
              return Scaffold(
                body: Center(
                  child: Text('count: ${counter.value} ou $value'),
                ),
              );
            }),
        floatingActionButton: FloatingActionButton(
          child: const Icon(Icons.plus_one),
          onPressed: () => counter.value += 1,
        ),
      ),
    );
  }
}