カウンターアプリ 2

Riverpod をインストールするでパッケージをインストールしておくこと。

lib\providers\counter.dartlib\main.dart

import 'package:riverpod_annotation/riverpod_annotation.dart';

part 'counter.g.dart';

@riverpod
class Counter extends _$Counter {
  @override
  int build() => 0;

  void increment() => state++;
  void decrement() => state--;
}

import 'package:flutter/material.dart';
import 'package:flutter_counter/providers/counter.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';

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

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
        useMaterial3: true,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends ConsumerWidget {
  const MyHomePage({super.key, required this.title});

  final String title;

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    // WidgetRef refで状態にアクセスできる
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Theme.of(context).colorScheme.inversePrimary,
        title: Text(title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            const Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '${ref.watch(counterProvider)}', // ref.watch(xxxProvider)で変更を検知しつつ値を読み込むことができる
              style: Theme.of(context).textTheme.headlineMedium,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () => ref
            .read(counterProvider.notifier)
            .increment(), // ref.read(xxxProvider.notifier).methodName()でメソッドを呼ぶことができる
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ),
    );
  }
}

実行前にdart run build_runner watch --delete-conflicting-outputsを実行してlib\counter.g.dartを生成すること。