What is dependency injection, and why is it a generally recommended practice for structuring a Flutter application's various services and repositories?

Beginner

Answer

Dependency injection is a design approach where a class receives the specific objects it actually depends on, such as an API client or a database repository, from an outside source rather than creating those dependencies directly within itself, and following this approach makes a class's code considerably easier to test, since a real dependency can easily be swapped out for a fake or mock version during testing, and also makes the overall codebase more flexible, since a specific implementation of a dependency can be changed in one central place without needing to modify every single individual class that happens to use it.

class OrderService {
  final ApiClient apiClient;
  OrderService(this.apiClient); // Injected rather than created internally
}

Real-world example An OrderService class receives its required ApiClient as a constructor parameter rather than creating one directly inside itself, letting a test easily substitute a fake ApiClient to verify the OrderService's own logic in complete isolation.

Common follow-ups: What is the difference between constructor injection and using a dedicated service locator?;Why is dependency injection considered particularly important for effective unit testing?

Unit Testing in Flutter;Flutter Architecture Patterns (MVVM & Clean Architecture)

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