Getting Started with Kotlin Multiplatform

Getting Started with Kotlin Multiplatform

Kotlin Multiplatform (KMP) has revolutionized the way we think about cross-platform development. Instead of maintaining separate codebases for different platforms, KMP allows you to share business logic while keeping platform-specific UI code native.

Why Choose Kotlin Multiplatform?

Benefits

  • Code Reuse: Share business logic, networking, and data models across platforms
  • Native Performance: Platform-specific implementations ensure optimal performance
  • Gradual Adoption: Integrate KMP into existing projects incrementally
  • Type Safety: Leverage Kotlin's strong type system across all platforms

Supported Platforms

  • Android
  • iOS
  • JVM (Desktop, Server)
  • JavaScript (Web)
  • Native (Linux, Windows, macOS)

Setting Up Your First KMP Project

Prerequisites

Before getting started, make sure you have:

  • IntelliJ IDEA or Android Studio
  • Kotlin plugin (latest version)
  • Android SDK
  • Xcode (for iOS development)

Project Structure

shared/
├── src/
│   ├── commonMain/kotlin/     # Shared code
│   ├── androidMain/kotlin/    # Android-specific code
│   ├── iosMain/kotlin/        # iOS-specific code
│   └── commonTest/kotlin/     # Shared tests
├── androidApp/                # Android application
└── iosApp/                    # iOS application

Creating Shared Business Logic

Here's a simple example of shared code:

// commonMain/kotlin/NetworkClient.kt
class NetworkClient {
    suspend fun fetchUser(id: String): User {
        // Shared networking logic
        return httpClient.get("/users/$id")
    }
}

data class User(
    val id: String,
    val name: String,
    val email: String
)

Platform-Specific Implementations

Sometimes you need platform-specific implementations:

// commonMain/kotlin/PlatformName.kt
expect fun getPlatformName(): String

// androidMain/kotlin/PlatformName.kt
actual fun getPlatformName(): String = "Android"

// iosMain/kotlin/PlatformName.kt
actual fun getPlatformName(): String = "iOS"

Best Practices

  1. Start Small: Begin by sharing data models and business logic
  2. Keep UI Native: Use platform-specific UI frameworks for the best user experience
  3. Test Thoroughly: Write comprehensive tests for your shared code
  4. Use Dependency Injection: Libraries like Koin work great with KMP
  5. Leverage Coroutines: For asynchronous programming across platforms

Common Challenges and Solutions

Dependency Management

Not all libraries support KMP. Consider these alternatives:

  • Ktor for networking (instead of Retrofit/OkHttp)
  • SQLDelight for databases (instead of Room)
  • Kotlinx.datetime for date/time handling

iOS Integration

When working with iOS:

  • Use @ObjC annotations for better Swift interop
  • Be mindful of memory management
  • Consider using Cocoapods for dependency management

Conclusion

Kotlin Multiplatform offers an excellent balance between code sharing and platform-specific optimization. While there's a learning curve, the benefits of reduced development time and consistent business logic make it worth the investment.

Start with a small shared module in your existing project and gradually expand as you become more comfortable with the ecosystem.

Resources

Happy coding with Kotlin Multiplatform! 🚀