Kotlin Multiplatform Development Guide

What Is Kotlin Multiplatform?

Kotlin Multiplatform (KMP) is a technology from JetBrains that allows developers to share business logic across multiple platforms, including Android, iOS, desktop, and web, while keeping native UI and platform-specific code where it matters most. Unlike frameworks that force a single rendering engine, KMP embraces each platform's native strengths.

Why Kotlin Multiplatform Matters

The promise of cross-platform development has existed for years, but most solutions require compromises. Kotlin Multiplatform takes a pragmatic approach by sharing only what makes sense to share. Here is why that matters:

• Code reuse without sacrifice: Share networking, data models, and business logic while writing native UI
• Gradual adoption: Integrate into existing projects without a full rewrite
• Native performance: Compiled code runs natively on each target platform
• Strong ecosystem: Backed by JetBrains with robust IDE support and growing library ecosystem

Architecture Overview

The Shared Module

At the heart of every KMP project is the shared module. This Kotlin module contains platform-independent code organized into common source sets. You write your business logic, data models, repository patterns, and utility functions here once.

Platform-Specific Implementations

When platform-specific APIs are needed, KMP uses the expect/actual mechanism. You declare an expected interface in common code and provide actual implementations for each target:

• expect: Declares a function or class signature in common code
• actual: Provides the platform-specific implementation

Target Platforms

KMP supports a wide range of compilation targets:

1. JVM: Android apps and server-side applications
2. Native: iOS via Kotlin/Native, plus macOS, Linux, and Windows
3. JavaScript: Browser and Node.js applications
4. WebAssembly: Emerging target for high-performance web apps

Setting Up a KMP Project

Project Structure

A typical KMP project follows this structure:

• shared/ - Common code shared across platforms
• androidApp/ - Android-specific UI and configuration
• iosApp/ - iOS-specific UI built with SwiftUI or UIKit
• desktopApp/ - Desktop application using Compose for Desktop

Dependency Management

KMP uses Gradle for build management. Dependencies can be declared for common code or specific platforms. Many popular libraries now offer KMP-compatible versions:

• Ktor: Multiplatform HTTP client and server framework
• SQLDelight: Type-safe SQL with multiplatform database drivers
• Kotlinx.serialization: Multiplatform JSON and other format serialization
• Koin: Lightweight dependency injection for KMP

Compose Multiplatform

JetBrains has extended Jetpack Compose beyond Android with Compose Multiplatform. This declarative UI framework now runs on Android, iOS, desktop, and web from a single codebase. While still maturing on iOS, it represents a compelling option for teams wanting maximum code sharing.

When to Use Compose Multiplatform

Real-World Use Cases

Major companies have adopted Kotlin Multiplatform in production. Netflix uses KMP for shared logic in their mobile apps. Cash App shares business logic across Android and iOS. Philips uses KMP in healthcare applications requiring high reliability.

At Ekolsoft, our development teams use Kotlin Multiplatform to deliver cross-platform solutions that reduce development time and maintenance costs while maintaining the quality and performance our clients expect.

Best Practices

Start Small

Begin by sharing a single module, such as networking or data models. Validate the workflow and expand gradually. This approach minimizes risk and builds team confidence.

Invest in Testing

KMP allows writing tests in common code that run on all platforms. Take advantage of this to establish a comprehensive test suite early:

• Unit test shared business logic in the common source set
• Write platform-specific tests for actual implementations
• Use integration tests to verify cross-platform behavior

Handle Platform Differences Gracefully

Not every API has a direct equivalent across platforms. Use the expect/actual pattern judiciously, and consider creating abstraction layers that normalize platform differences behind clean interfaces.

Challenges and Considerations

Despite its strengths, KMP presents some challenges:

• iOS interop complexity: Kotlin/Native has memory management nuances that differ from Swift
• Build times: Multi-target builds can be slower than single-platform builds
• Library availability: Not all libraries support KMP yet, though the ecosystem is growing rapidly
• Team skill requirements: Developers need familiarity with Kotlin and target platform ecosystems

Kotlin Multiplatform is not about replacing native development. It is about making cross-platform development practical, performant, and maintainable for real-world applications.

Conclusion

Kotlin Multiplatform offers a mature, pragmatic approach to cross-platform development that respects the strengths of each platform. By sharing business logic while preserving native UI capabilities, KMP delivers genuine code reuse without the compromises that have plagued earlier cross-platform solutions. Whether you are building mobile, desktop, or web applications, KMP deserves serious consideration in your technology strategy.