test.dart

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

const Color darkBlue = Color.fromARGB(255, 18, 32, 47);

class CountController extends StateNotifier<AsyncValue<int>> {
  CountController() : super(const AsyncData<int>(0));

  Future<void> up() async {
    state = const AsyncLoading<int>();

    state = await AsyncValue.guard<int>(() async {
      return state.value ?? 0 + 1;
    });
  }
}

final countProvider =
StateNotifierProvider.autoDispose<CountController, AsyncValue<int>>((ref) {
  return CountController();
});

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData.dark().copyWith(
        scaffoldBackgroundColor: darkBlue,
      ),
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: Center(
          child: MyWidget(),
        ),
      ),
    );
  }
}

class MyWidget extends ConsumerWidget {
  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final count = ref.watch(countProvider).value.toString();
    return SafeArea(
      child: Column(
        children: [
          Text(
            'Count: $count',
            style: Theme.of(context).textTheme.headline4,
          ),
          ElevatedButton(
            onPressed: () => ref.read(countProvider.notifier).up(),
            style: ElevatedButton.styleFrom(
              shape: const StadiumBorder(),
            ),
            child: const Text('up'),
          )
        ],
      ),
    );
  }
}