Sample change notifier

change_notifier.dart

class Person extends ChangeNotifier {
  Person({this.name, this.age});
  final String name;
  int age;
         
  void increaseAge() {
    this.age++;
    notifyListeners();
  }
}
void main() {
  runApp(
    ChangeNotifierProvider(
      create: (_) => Person(name: "Joe", age: 28),
      child: MyApp(),
    ),
  );
}