Code Sharing and Multi-Platform Modules
Learn how to share code across Android and iOS while preserving the platform-standard experience.
Have you ever built the same mobile feature twice, once for Android and once for iOS, and thought, “There has to be a better way”? You’re not alone. As a mobile developer, duplicating logic across platforms can be time-consuming and frustrating.
In this lesson, we’ll learn how to share core app logic across platforms without sacrificing the platform-specific experience users expect. We’ll look at how mobile apps are typically organized into layers, a structure often called modular architecture, and see which layers are best suited for code sharing. Along the way, we’ll explore how tools like Kotlin Multiplatform, Rust, C++, or JavaScript can help us write logic once and reuse it across Android and iOS.
Note: Code sharing should not be confused with building a single cross-platform app. It means developing fully platform-optimized apps for Android and iOS, each with its own interface and platform conventions. This is done while reusing only the parts of the codebase that are safe and practical to share.
By the end, we’ll understand what parts of our app make sense to share, how to start building shared modules, and how to decide when it’s better to stick with platform-specific code.
Before discussing the details of sharing code, let’s consider why code sharing matters in mobile development.
Understanding why code sharing matters in mobile apps
When we build for both Android and iOS, we’re usually solving the same problems twice. That means writing the same business rules, duplicating the same API calls, and maintaining similar model classes for each platform. Overtime, this not only increases the workload but also introduces risks. A bug fixed in one platform might still be lurking in the other. Features released on one side may take days or weeks to catch up on the other.
The illustration below contrasts a less ideal approach, where shareable modules are built separately for iOS and Android, with a better approach that reuses them across both platforms for easier maintenance and less duplication:
Sharing code where it makes sense, such as business logic, data access, and network ...