Riverpodをインストールする + StateProviderを使う (Flutter)

$ flutter --version
Flutter 3.3.4 • channel stable • https://github.com/flutter/flutter.git
Framework • revision eb6d86ee27 (3 weeks ago) • 2022-10-04 22:31:45 -0700
Engine • revision c08d7d5efc
Tools • Dart 2.18.2 • DevTools 2.15.0

dependencies:
  flutter:
    sdk: flutter

  flutter_hooks: ^0.18.5+1
  hooks_riverpod: ^2.0.2
...

import 'package:flutter/material.dart';
import 'package:flutter_hooks/flutter_hooks.dart';
import 'package:hooks_riverpod/hooks_riverpod.dart';

void main() {
  runApp(ProviderScope(child: MyApp()));
}

final counterProvider = StateProvider((ref) => 1);

class MyApp extends ConsumerWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context, WidgetRef ref) {
    var counter = ref.watch(counterProvider.notifier);

    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: const Text('My First app'),
        ),
        body: Text('count: ${ref.watch(counterProvider)}'),
        floatingActionButton: FloatingActionButton(
          onPressed: () => {counter.update((state) => state + 2)},
          child: const Icon(Icons.add),
        ),
      ),
    );
  }
}