StatelessWidget: Riverpod

main.dart

import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';

class CounterNotifier extends ChangeNotifier {
  int _count = 0;

  void add() {
    _count++;
    notifyListeners();
  }

  void subtract() {
    _count--;
    notifyListeners();
  }
}

final counterProvider = ChangeNotifierProvider(
  (ref) => CounterNotifier(),
);

void main() => runApp(ProviderScope(child: MyApp()));

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: const Text('FlutterZero')),
        body: Center(
          child: Consumer(
            builder: (context, ref, child) {
              final count = ref.watch(counterProvider);
              return Row(
                mainAxisAlignment: MainAxisAlignment.center,
                children: [
                  IconButton(
                    icon: Icon(Icons.remove),
                    onPressed: () => count.subtract(),
                  ),
                  Text(
                    count._count.toString(),
                    style: TextStyle(fontSize: 30),
                  ),
                  IconButton(
                    icon: Icon(Icons.add),
                    onPressed: () => count.add(),
                  ),
                ],
              );
            },
          ),
        ),
      ),
    );
  }
}