riverpod-providers（Riverpod 提供商）

Riverpod — Providers

Instructions

Providers are the central feature of Riverpod: memoized functions that cache their result and let multiple widgets (or other providers) access the same value. They are declared as top-level final variables. State lives in a ProviderContainer (or ProviderScope in Flutter), not in the provider itself.

Provider variants

• Sync vs Future vs Stream: Match the return type of your function (int, Future<T>, Stream<T>).
• Unmodifiable: Widgets only read the value. Use for computed or fetched data.
• Modifiable: Expose a Notifier with a build() method and custom methods; widgets call ref.read(provider.notifier).someMethod(). Use when the UI must update state.

Pick the type based on what you want to return; the provider type follows naturally. FutureProvider / AsyncNotifierProvider are the most common.

Creating a provider (unmodifiable / functional)

Manual:

final userProvider = FutureProvider<User>((ref) async {
  final response = await http.get('https://api.example.com/user/123');
  return User.fromJson(response.body);
});

Code generation: Annotate a top-level function with @riverpod. First parameter must be Ref ref. The generated provider name is functionNameProvider.

@riverpod
Future<User> user(Ref ref) async {
  final response = await http.get('https://api.example.com/user/123');
  return User.fromJson(response.body);
}

Modifiers: .autoDispose (or @Riverpod(keepAlive: true) to disable) and .family for parameters. See riverpod-auto-dispose and riverpod-family.

Creating a provider (modifiable / Notifier)

Manual: Use a NotifierProvider (or AsyncNotifierProvider / StreamNotifierProvider) with a Notifier class that extends Notifier<T>, AsyncNotifier<T>, or StreamNotifier<T>. Override build(); do not put logic in the constructor (ref/state are not available yet). Public methods are called via ref.read(provider.notifier).method().

final counterProvider = NotifierProvider<CounterNotifier, int>(CounterNotifier.new);

class CounterNotifier extends Notifier<int> {
  @override
  int build() => 0;

  void increment() => state++;
}

Code generation: Annotate a class that extends _$ClassName. Override build(); add custom methods. Same rule: no logic in the constructor.

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

  void increment() => state++;
}

Using providers

1. Flutter: Wrap the app in ProviderScope. Use Consumer, ConsumerWidget, or ConsumerStatefulWidget to get a ref and call ref.watch(provider) or ref.read(provider).
2. Dart only: Create a ProviderContainer(), then container.read(provider) or container.listen(...). Call container.dispose() when done.
3. Inside another provider: Use the Ref passed to the provider function (or this.ref in a Notifier) to ref.watch / ref.read other providers.

Example in a widget:

return Consumer(
  builder: (context, ref, _) {
    final helloWorld = ref.watch(helloWorldProvider);
    return Text(helloWorld);
  },
);

You can declare multiple providers that return the same type; they are independent. For more detail on Ref, containers, modifiers, and notifier rules, see reference.md.