Refactoring Legacy Flutter Apps to Use Riverpod 3.0

Introduction

Migrating a legacy Flutter app to Riverpod 3.0 improves maintainability, testability, and performance in mobile development. Riverpod’s decoupled architecture and compile-time safety reduce runtime bugs. This tutorial walks through key steps: understanding Riverpod concepts, preparing your codebase, refactoring state management, and validating functionality.

Understanding Riverpod 3.0 Basics

Riverpod 3.0 introduces a unified approach to providers, combining sync, async, and code-generated notifiers. Core concepts:

• Provider: a read-only value.

• StateNotifierProvider / AsyncNotifierProvider: mutable and asynchronous state containers.

• ref.watch / ref.read: subscribe or read providers without rebuilding unnecessarily.

Example: a simple counter using StateNotifierProvider:

final counterProvider = StateNotifierProvider<Counter, int>((ref) => Counter());
class Counter extends StateNotifier<int> {
  Counter() : super(0);
  void increment() => state++;
}

Use ref.watch(counterProvider) in your widget to rebuild on state changes.

Preparing Your Legacy Codebase

1. Audit state patterns: identify uses of setState, InheritedWidget, and Provider or Bloc.

2. Extract business logic: move stateful logic into dedicated classes (e.g., ChangeNotifier subclasses).

3. Add Riverpod dependencies:

dependencies:
  flutter_riverpod: ^3.0.0
dev_dependencies:
  riverpod_generator: ^3.0.0
  build_runner

4. Configure code generation by annotating AsyncNotifier classes or using Riverpod’s built-in providers.

Aim for a clear separation between UI, business logic, and data layers before refactoring.

Migrating Providers and State

Convert existing ChangeNotifier or Bloc classes to Riverpod notifiers:

1. Change ChangeNotifier to StateNotifier:

// Legacy ChangeNotifier
class CartModel extends ChangeNotifier {
  final List<Item> items = [];
  void add(Item item) {
    items.add(item);
    notifyListeners();
  }
}

// Refactored with Riverpod
final cartProvider = StateNotifierProvider<CartNotifier, List<Item>>(
  (ref) => CartNotifier(),
);
class CartNotifier extends StateNotifier<List<Item>> {
  CartNotifier(): super([]);
  void add(Item item) => state = [...state, item];
}

2. Handle async operations with AsyncNotifierProvider:

@riverpod
class Auth extends _$Auth {
  @override
  Future<User> build() async {
    return await AuthService.signIn();
  }
}

Run flutter pub run build_runner build to generate supporting code.

3. Replace Provider.of or context.read with ref.watch or ref.read in widgets.

Testing and Optimization

Riverpod’s override mechanism simplifies testing. Use ProviderContainer to inject mock services:

void main() {
  final container = ProviderContainer(overrides: [
    authProvider.overrideWithValue(AsyncValue.data(MockUser())),
  ]);
  final auth = container.read(authProvider);
  expect(auth.value, isA<MockUser>());
}

Performance tips:

• Use ref.listen for side effects instead of rebuilding widgets.

• Split heavy providers into smaller ones to limit rebuild scopes.

• Employ Riverpod’s devtools for inspecting provider interactions.

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Conclusion

Refactoring to Riverpod 3.0 transforms legacy Flutter apps into robust, testable, and performant mobile applications. By understanding provider types, preparing the codebase, migrating state logic, and leveraging Riverpod’s test utilities, you’ll modernize your architecture and streamline future feature development.