changenotifier_example.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) =>const  MaterialApp(title: 'Material App', home: Home());
}

class Home extends StatefulWidget {
  const Home({Key? key}) : super(key: key);

  @override
  _HomeState createState() => _HomeState();
}

class _HomeState extends State<Home> {
  late final notifier = SomeNotifier();
  void listner() {
    setState(() {});
    print('Notifier called notifyListeners');
  }

  @override
  void initState() {
    super.initState();
    notifier.addListener(listner);
  }

  @override
  void dispose() {
    notifier.removeListener(listner);
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(),
      body: Center(child: Text('Count: ${notifier.count}')),
      floatingActionButton: FloatingActionButton(child: const Icon(Icons.add), onPressed: notifier.increment),
    );
  }
}

class SomeNotifier extends ChangeNotifier {
  int _count = 0;
  int get count => _count;
  set count(int value) {
    _count = value;
    notifyListeners();
  }

  void increment() => count++;
}