How do you use dependency injection in Flutter?

Short answer

Pass dependencies through a constructor or a composition root, so they can be swapped for a fake or another implementation without modifying the consumer.

Explanation

Injecting dependencies makes ownership and tests clear. Choose constructor injection in most cases, and use a container only when it actually reduces repeated wiring; fully hiding dependencies makes reading harder.

Code example

class UserPresenter {
  UserPresenter(this.repository);
  final UserRepository repository;
}

Common mistakes

• Creating a dependency inside the class and then trying to mock it later.
• Passing a service locator into every method instead of a clear contract.

Follow-up questions

• What is the practical difference between a fake, a mock, and a stub in Flutter tests?

Sources

• Flutter docs — App architecture guide