Dependency Injection Best Practices in Flutter

Introduction

Dependency injection (DI) is a cornerstone of maintainable Flutter mobile development. DI separates object creation from usage, improves testability, and reduces coupling. This article outlines pragmatic DI best practices for Flutter apps, focusing on patterns that scale across small utilities and large, feature-rich mobile projects.

Choose The Right DI Approach

There are three common DI approaches in Flutter: manual constructor injection, service locators (e.g., get_it), and provider-based dependency graphs. Choose based on app size and team needs:

• For small apps, constructor injection keeps code explicit and easy to reason about.

• For medium to large apps, combine provider or Riverpod for widget-scoped dependencies with get_it for application-singletons.

• Avoid opaque global singletons for logic that needs testing; prefer abstractions and interfaces.

Use the keyword flutter when evaluating packages and patterns: prefer solutions that integrate cleanly with Flutter's widget lifecycle for predictable mobile development behavior.

Register Services At App Start

Centralize service registration near your app entrypoint so dependency graphs are predictable and reproducible. Register singletons, analytics, and API clients before runApp so widgets can safely assume availability.

Example using get_it:

final getIt = GetIt.instance;
void setup() {
  getIt.registerLazySingleton<ApiClient>(() => ApiClientImpl());
  getIt.registerFactory<AuthRepository>(() => AuthRepository(getIt<ApiClient>()));
}

Keep registration code compact and split by feature module if your app grows. Avoid registering concrete UI classes at the root—register interfaces and factories instead.

Make Dependencies Explicit

Prefer constructor injection to keep dependencies visible and immutable. Explicit dependencies make unit testing trivial and reduce hidden coupling.

When a ViewModel or Controller needs a repository, inject it via the constructor rather than pulling it from a global locator inside the class:

class LoginViewModel {
  final AuthRepository authRepository;
  LoginViewModel(this.authRepository);
  Future<void> login(...) => authRepository.login(...);
}

This approach lets tests create the ViewModel with mocked repositories without touching app-wide state. Use abstract interfaces for repositories and services so tests can substitute lightweight fakes.

Manage Scopes And Lifecycle

Flutter apps have multiple lifecycles: app-level singletons, route-scoped objects, and widget-scoped controllers. Use scopes intentionally:

• App singletons for things like logging, analytics, and HTTP clients.

• Route-scoped services for resources that should be recreated when navigating (e.g., flow-specific state).

• Widget-scoped dependencies for tightly-coupled UI logic.

Use Provider, Riverpod, or InheritedWidgets to scope dependencies to a subtree. When using get_it, combine it with factories to ensure objects are recreated for each route/session. Always pair resources that require disposal (streams, controllers) with lifecycle-aware providers (ChangeNotifierProvider, Provider with dispose callbacks).

Favor Interfaces And Small Modules

Design services as small, focused interfaces. This reduces the blast radius when changes occur and makes mocking easier. Group registration and tests by feature module (auth, payments, offline sync) to keep DI configuration discoverable.

• Define clear contracts (abstract classes) for external integrations.

• Keep implementation details hidden behind interfaces so swapping HTTP clients or persistence layers is painless.

• Write tiny modules' setup functions and call them from the main setup to keep bootstrapping readable.

Test With DI In Mind

Make testing first-class: use constructor injection and interfaces so units are trivial to instantiate in tests. Mock networks, timers, and platform channels behind abstractions. When using service locators, provide a way to reset or override registrations between tests to avoid cross-test interference.

Best practices for testing:

• Use factories for objects that must be fresh per test.

• Avoid global mutable state; when necessary, reset between tests.

• Provide test-specific setups that mirror production registration to catch integration mismatches early.

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Conclusion

Good DI practice in Flutter balances explicit constructor injection with pragmatic use of scoping tools like Provider, Riverpod, or get_it for singletons. Centralize registration at app start, prefer interfaces and small modules, manage lifecycle via scopes, and design for testability from day one. Applying these practices makes Flutter mobile development more maintainable, easier to test, and resilient as your app grows.