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Flutter Mobile Development · レッスン

状態管理のためのRiverpod

堅牢でテストしやすい状態管理ライブラリであるRiverpodを学び、複雑なアプリで他のソリューションより優れている点を理解します。

「状態管理のためのRiverpod」はCoddyKit上の無料Flutter Mobile Developmentレッスンです。 これはレッスン3/4です。 下記で完全なレッスンを無料で読むことができます。その後、ブラウザ内の組み込みコードエディタと24時間対応のAIチューターでハンズオン演習できます。 これはFlutter Mobile Development学習パスの一部であり、ウェブとCoddyKitアプリ全体で進捗が同期されます。 Flutter Mobile Developmentコースには全4レッスンが含まれています。

このレッスンの一部はまだ翻訳されておらず、英語で表示されています。

Welcome to Riverpod!

Riverpod is a popular state management library for Flutter that aims to be simple, robust, and testable. It's a reimagined version of the Provider package, designed to address some of its limitations.

Think of Riverpod as a powerful toolkit for managing all the data in your app, from user settings to fetched data, in a safe and predictable way.

Riverpod's Core Strengths

Riverpod offers several key advantages:

  • Compile-time Safety: Catches errors early, before your app even runs.
  • Testability: Makes it easy to test your business logic in isolation.
  • Auto-Dispose: Providers can automatically clean up resources when no longer needed.
  • No Widget Tree Dependency: Providers don't rely on the widget tree, making them more flexible.

It helps you write cleaner, more maintainable code.

Setting Up Your App

To use Riverpod, first add the flutter_riverpod package to your pubspec.yaml. Then, wrap your entire application with a ProviderScope widget. This widget stores the state of all your providers.

Here's how to set it up:

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

void main() {
  runApp(
    // Wrap your app in a ProviderScope
    ProviderScope(
      child: MyApp(),
    ),
  );
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Text('Hello Riverpod'),
    );
  }
}

Introducing Providers

Providers are the core building blocks of Riverpod. They hold a piece of state and allow you to access it from anywhere in your app.

The simplest provider is a Provider, which holds an immutable value. You define it globally, making it accessible throughout your application.

import 'package:flutter_riverpod/flutter_riverpod.dart';

// A simple Provider that holds an immutable string.
final greetingProvider = Provider<String>((ref) {
  return 'Hello from Riverpod!';
});

// You can also provide numbers, objects, etc.
final counterProvider = Provider<int>((ref) => 0);

Consuming Providers with `ConsumerWidget`

To read a provider's value in your UI, you use a ConsumerWidget. This widget gives you access to a WidgetRef (often named ref), which lets you 'watch' or 'read' providers.

ref.watch() makes your widget rebuild when the provider's value changes.

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

final greetingProvider = Provider<String>((ref) {
  return 'Hello Riverpod User!';
});

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: ConsumerWidget(
        builder: (context, ref, child) {
          final greeting = ref.watch(greetingProvider);
          return Scaffold(
            appBar: AppBar(title: Text('Riverpod App')),
            body: Center(child: Text(greeting)),
          );
        },
      ),
    );
  }
}

Mutable State with `StateProvider`

When you need to change a piece of state directly, use a StateProvider. It exposes a StateController, which has a state property you can modify.

This is perfect for simple UI states like a toggle or a counter.

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

// A StateProvider for a simple counter.
final counterProvider = StateProvider<int>((ref) => 0);

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: ConsumerWidget(
        builder: (context, ref, child) {
          final count = ref.watch(counterProvider);
          return Scaffold(
            appBar: AppBar(title: Text('Counter App')),
            body: Center(
              child: Text(
                'Count: $count',
                style: TextStyle(fontSize: 24),
              ),
            ),
            floatingActionButton: FloatingActionButton(
              onPressed: () => ref.read(counterProvider.notifier).state++,
              child: Icon(Icons.add),
            ),
          );
        },
      ),
    );
  }
}

`StateNotifierProvider` for Logic

For more complex state that involves business logic (e.g., fetching data, managing lists), you'll use a StateNotifier with StateNotifierProvider.

StateNotifier is a class you extend, and it holds your state. The provider then exposes an instance of your notifier.

import 'package:flutter_riverpod/flutter_riverpod.dart';

// 1. Define your state class (immutable recommended)
class Todo { 
  final String id; 
  final String description; 
  final bool completed; 
  Todo(this.id, this.description, this.completed); 
}

// 2. Create a StateNotifier to manage the state
class TodosNotifier extends StateNotifier<List<Todo>> {
  TodosNotifier() : super([]); // Initial state is an empty list

  void addTodo(String description) {
    state = [...state, Todo(DateTime.now().toString(), description, false)];
  }

  void toggle(String id) {
    state = [ 
      for (final todo in state) 
        if (todo.id == id) 
          Todo(todo.id, todo.description, !todo.completed) 
        else 
          todo, 
    ];
  }
}

// 3. Create the StateNotifierProvider
final todosProvider = StateNotifierProvider<TodosNotifier, List<Todo>>((ref) {
  return TodosNotifier();
});

Async Data with `FutureProvider`

Riverpod makes handling asynchronous data (like network requests) a breeze with FutureProvider and StreamProvider.

A FutureProvider exposes an AsyncValue, which gracefully handles loading, error, and data states in your UI.

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

// A FutureProvider that simulates fetching data.
final userProvider = FutureProvider<String>((ref) async {
  await Future.delayed(Duration(seconds: 2)); // Simulate network delay
  return 'John Doe';
});

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: ConsumerWidget(
        builder: (context, ref, child) {
          final userAsyncValue = ref.watch(userProvider);
          return Scaffold(
            appBar: AppBar(title: Text('Async Data')),
            body: Center(
              child: userAsyncValue.when(
                loading: () => CircularProgressIndicator(),
                error: (err, stack) => Text('Error: $err'),
                data: (user) => Text('User: $user', style: TextStyle(fontSize: 24)),
              ),
            ),
          );
        },
      ),
    );
  }
}

`ref.read` vs `ref.watch`

When interacting with providers, you'll primarily use two methods on the ref object:

  • ref.watch(provider): Listens to changes in a provider. If the provider's state changes, the widget or provider watching it will rebuild/re-execute. Use this in build methods.
  • ref.read(provider): Reads a provider's current value once, without listening for future changes. Ideal for one-off actions, like button presses or initial setup.

Avoid ref.read in build methods unless you specifically don't want rebuilds.

Riverpod Provider Types

Which Riverpod provider types are best suited for managing a simple counter (a single integer that can be incremented/decremented) and for handling complex business logic with multiple actions (e.g., adding/removing items from a to-do list)?

Riverpod Recap

Great job! You've explored Riverpod, a powerful and modern state management solution for Flutter.

  • We learned about ProviderScope for app setup.
  • We used Provider for immutable data and StateProvider for simple mutable state.
  • For complex logic, StateNotifierProvider with StateNotifier is key.
  • FutureProvider helps manage async data gracefully.
  • Remember ref.watch for listening and ref.read for one-time access.

Riverpod's compile-time safety and testability make it an excellent choice for robust Flutter applications!

よくある質問

「状態管理のためのRiverpod」レッスンは無料ですか？

はい。「状態管理のためのRiverpod」の完全なテキストはこのウェブで無料で読めます。インタラクティブに演習し（組み込みコードエディタと24時間対応のAIチューター）、Flutter Mobile Developmentコースの残りをアンロックするには、CoddyKit PROにアップグレードしてください。 Flutter Mobile Developmentコースには全4レッスンが含まれています。

「状態管理のためのRiverpod」で何を学びますか？

堅牢でテストしやすい状態管理ライブラリであるRiverpodを学び、複雑なアプリで他のソリューションより優れている点を理解します。 ブラウザで直接実行するハンズオンコードでFlutter Mobile Developmentを演習し、24時間対応のAIチューターがレッスンを進める中での質問に答えます。

Flutter Mobile Developmentを始めるのに経験は必要ですか？

事前経験は必要ありません。CoddyKitのFlutter Mobile Developmentは初級者から上級者向けに構成されているため、ここから始めるか最初から始めて、自分のペースで進むことができます。 これはレッスン3/4です。

「状態管理のためのRiverpod」レッスンにはどのくらい時間がかかりますか？

ほとんどのCoddyKitレッスンは約5～10分かかります。各レッスンはコンパクトでインタラクティブなので、着実に進歩し、ウェブとアプリ全体で正確に前回の場所から再開できます。

このFlutter Mobile Developmentレッスンでコードを書いて実行できますか？

はい。すべてのFlutter Mobile Developmentレッスンに組み込みコードエディタが含まれているため、ブラウザでリアルコードを書いて実行し、即座のAIフィードバックを取得できます。ローカル設定は不要です。

このコースのすべてのレッスン

  1. setStateとInheritedWidget
  2. Providerパッケージの基礎
  3. 状態管理のためのRiverpod
  4. Streams による BLoC パターン
← Flutter Mobile Developmentに戻る