Layered Architecture for KMP
Separate data, domain and presentation cleanly.
Layered Architecture for KMP is a free Kotlin Multiplatform Academy lesson on CoddyKit — lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Kotlin Multiplatform Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
One Codebase, Many Apps
As your KMP app grows, shared code can turn into a tangle. A clear layered architecture keeps every piece in its lane so both apps stay easy to change.
Three Classic Layers
Most KMP apps settle on three layers: data, domain and presentation. Each has one job, and dependencies flow in a single, predictable direction.
The Data Layer
The data layer talks to the outside world: Ktor for HTTP, SQLDelight for storage. It fetches raw bytes and hands clean data upward, hiding the details.
The Domain Layer
The domain layer holds your business rules and models. It knows nothing about HTTP or SQL, so it stays pure, portable and trivially testable.
The Presentation Layer
The presentation layer prepares state for the screen. Shared ViewModels live here, turning domain data into the StateFlow each UI collects.
Dependencies Point Inward
The golden rule: outer layers depend on inner ones, never the reverse. Presentation knows domain; domain knows nothing about either neighbour.
Talk Through Interfaces
Layers connect through interfaces, not concrete classes. Domain declares what it needs; data provides the implementation, so you can swap pieces freely.
interface UserRepository {
suspend fun load(id: String): User
}Models per Layer
Each layer can own its shapes: a network DTO in data, a clean model in domain. Mapping between them keeps API quirks from leaking into your rules.
Why Bother Separating
Separation pays off when requirements shift. Swap a REST API for GraphQL and only the data layer changes; domain and presentation never notice.
It All Lives Shared
Data, domain and presentation can all sit in commonMain. Both Android and iOS reuse the entire stack and only supply the final native screen.
Start Simple
You do not need ten layers on day one. Begin with these three, keep the dependency arrows clean, and let the structure grow only when it earns its keep. 🙂
Quick Check
Which way should dependencies flow between layers?
Recap
You split shared code into data, domain and presentation, pointed dependencies inward, and connected layers through interfaces. Clean lanes, easy changes. 🎉
Frequently asked questions
Is the “Layered Architecture for KMP” lesson free?
Yes — the full text of “Layered Architecture for KMP” is free to read here on the web, and the Kotlin Multiplatform Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Kotlin Multiplatform Academy course, upgrade to CoddyKit PRO.
What will I learn in “Layered Architecture for KMP”?
Separate data, domain and presentation cleanly. You practise Kotlin Multiplatform Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Kotlin Multiplatform Academy?
No prior experience is required. Kotlin Multiplatform Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Layered Architecture for KMP” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Kotlin Multiplatform Academy lesson?
Yes. Every Kotlin Multiplatform Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Layered Architecture for KMP
- Use Cases & Domain Boundaries
- Split Shared Code into Modules
- Decide What Stays Native