Riverpod Patterns

Iron Law: Always use the correct Riverpod provider type for the use case; never use StateProvider for async data or FutureProvider for mutable state.

Riverpod Patterns

Correct Riverpod patterns for Flutter state management with code_generation style.

When to use: Writing or reviewing Riverpod providers, AsyncNotifier, AsyncValue.when, ref.watch vs ref.read, family providers, or provider lifecycle.

Process:

1. Identify pattern needed from user request
2. Load reference: Read reference/riverpod-core-patterns.md for code examples and rules
3. Apply patterns using loaded reference
4. Verify: Confirm ref.watch is only in build(), ref.read only in callbacks, all AsyncValue states handled visibly

Quick Reference — Most Common Patterns

Provider Type Selection

// ✅ Read-only async data (API call, DB read)
@riverpod
Future<List<User>> userList(UserListRef ref) async {
  return ref.watch(userRepositoryProvider).getAll();
}

// ✅ Mutable state with async operations
@riverpod
class UserNotifier extends _$UserNotifier {
  @override
  Future<User> build(String userId) async {
    return ref.watch(userRepositoryProvider).getById(userId);
  }

  Future<void> update(UserUpdateDto dto) async {
    state = const AsyncValue.loading();
    state = await AsyncValue.guard(() =>
      ref.read(userRepositoryProvider).update(dto));
  }
}

// ❌ WRONG — never use StateProvider for async data
final userProvider = StateProvider<User?>((ref) => null); // no async support

AsyncValue.when — All 3 states required

// ✅ All 3 states handled visibly
ref.watch(userListProvider).when(
  data: (users) => UserListWidget(users: users),
  loading: () => const CircularProgressIndicator(),
  error: (err, stack) => ErrorWidget(message: err.toString()), // never swallow
);

// ❌ WRONG — skipLoadingOnReload hides loading state from user
ref.watch(userListProvider).when(
  skipLoadingOnReload: true, // only acceptable after explicit UX decision
  data: (users) => UserListWidget(users: users),
  loading: () => const SizedBox.shrink(), // invisible loading = silent failure
  error: (err, stack) => const SizedBox.shrink(), // swallowed error
);

ref.watch vs ref.read

// ✅ ref.watch — only inside build()
@override
Widget build(BuildContext context, WidgetRef ref) {
  final users = ref.watch(userListProvider); // rebuilds on change
  return UserListWidget(users: users.valueOrNull ?? []);
}

// ✅ ref.read — only inside callbacks/event handlers
void onButtonPressed(WidgetRef ref) {
  ref.read(userNotifierProvider.notifier).refresh(); // one-time action
}

// ❌ WRONG — ref.watch in a callback (causes infinite rebuild)
onPressed: () => ref.watch(userNotifierProvider.notifier).refresh(),

Reference Files

Error Handling

Provider not found: Ensure ProviderScope wraps the widget tree. Check that generated .g.dart files are up to date (dart run build_runner build).

AsyncValue stuck loading: Verify the repository method returns data. Use AsyncValue.guard() to catch and surface errors instead of silent failures.