Android Clean Architecture: Understanding the Domain Layer

Sean Coyle from ASOS breaks down the most misunderstood layer in Clean Architecture. If your ViewModels are bloated and your business logic is scattered everywhere, this deep dive into the Domain Layer will change how you structure Android apps.

This comprehensive guide explores the Domain Layer in Android Clean Architecture, explaining how Use Cases, Repository interfaces, and domain models work together to encapsulate business logic. Sean shares battle-tested practices from ASOS's production codebase, covering everything from threading strategies to dependency injection patterns.

Key Takeaways

• Use Cases should have exactly one public function following Single Responsibility Principle
• Domain Layer stays main-thread safe by delegating I/O to Data Layer
• Combine multiple repository flows in Use Cases, not ViewModels or Repositories
• Lazy injection reduces memory overhead for conditionally used Use Cases
• ViewModelScoped ensures Use Case instances persist throughout ViewModel lifecycle

The article reveals why ASOS restricts all data access to go through Use Cases, even for simple fetches, and how this decision impacts their modularization strategy.