What is Clean Architecture and how does it apply to Flutter?
Short Answer
Clean Architecture separates an app into independent layers — typically presentation, domain, and data — where inner layers (business logic) never depend on outer layers (UI, frameworks, databases), so business rules can be tested and reused independently of Flutter itself.
In a typical Flutter implementation: the presentation layer holds widgets and state management (Bloc/Riverpod/Provider), the domain layer holds pure-Dart entities and use cases (business rules with zero Flutter or package imports), and the data layer holds repositories and data sources (API clients, local databases) that implement interfaces defined in the domain layer.
The dependency rule flows inward: presentation depends on domain, data depends on domain, but domain depends on nothing Flutter-specific. This is enforced via the Dependency Inversion Principle — the domain layer defines a `UserRepository` interface (abstract class), and the data layer provides the concrete implementation, which gets injected at the outer edges (often via Provider/Riverpod or a DI container like `get_it`). The payoff is that you can unit test use cases with zero widgets, mock the repository easily, and swap a REST data source for GraphQL without touching business logic.
Common Mistakes
- ×Over-engineering tiny apps with the full three-layer structure when a simpler approach would do — Clean Architecture's value shows up as the app and team grow.
- ×Letting domain-layer code import Flutter packages (like `material.dart`), which breaks the whole point of the separation.
Interview Tips
- →Be ready to explain the Dependency Inversion Principle specifically — it's the mechanism that makes the layering actually work, not just a folder structure.
Related Questions
What is the Repository pattern?
The Repository pattern puts a single abstraction in front of however data is actually fetched or stored — network, local cache, database — so the rest of the app talks to one consistent interface and doesn't care where the data comes from.
What is Dependency Injection and how is it used in Flutter?
Dependency Injection means a class receives its dependencies from the outside (via constructor or a container) instead of creating them itself, which decouples classes from concrete implementations and makes them easy to test with substitutes.