Kotlin Multiplatform Architecture

Building the same app twice, once for Android and once for iOS, is expensive. Every bug gets fixed twice. Every feature gets built twice. And over time, the two versions quietly drift apart. Kotlin Multiplatform changes this equation. It lets you write your business logic, networking, and data layer once in shared Kotlin code, while keeping your user interface fully native on each platform. You get the speed of one codebase and the feel of two real native apps, without compromising on either.

This book is a complete, practical guide to designing and scaling real applications with Kotlin Multiplatform. You will start with the fundamentals: source sets, the expect and actual mechanism, and how shared and platform-specific code actually fit together. From there, you will build a full clean architecture, wire it together with dependency injection using Koin, connect it to real networking and local databases with Ktor and SQLDelight, and test every layer of it properly. By the end, you will know how to scale a shared codebase across a growing team, integrate it into existing native apps, and even publish it as a library others can depend on.

• Setting up a Kotlin Multiplatform project from scratch, and structuring it to scale
• Understanding source sets, the source set hierarchy, and how to organize shared versus platform-specific code
• A deep, practical look at expect and actual declarations, including common mistakes and better alternatives
• Applying clean architecture: domain layer, use case layer, data layer, and shared view models
• Dependency injection across platforms using Koin
• Building a shared networking layer with Ktor Client
• Local data persistence with SQLDelight
• Coroutines and Flow for shared asynchronous logic, including platform-specific concurrency pitfalls
• A complete testing strategy: unit tests, platform-specific tests, mocking, and continuous integration
• Scaling a codebase across growing teams, integrating shared code into existing native apps, and publishing multiplatform libraries

This book is written for Android and iOS developers who are tired of maintaining two versions of the same logic, and for software engineers and architects who need to make real decisions about where cross-platform code belongs and where it doesn't. If you already know Kotlin and want to go beyond tutorials into genuine architectural thinking, this book is for you. You do not need prior Kotlin Multiplatform experience. You do need a willingness to think carefully about structure, not just syntax.

You can keep fixing the same bug twice, or you can start building it right, once. Every chapter in this book moves you closer to a codebase your whole team can trust, on both platforms, at the same time. Get your copy today, and start building applications that scale the way they were always meant to.