Kotlin Multiplatform Mobile (KMM): Cross-Platform Development for iOS and Android

Kotlin Multiplatform Mobile (KMM) is revolutionizing cross-platform development by allowing developers to write code once and run it on both iOS and Android. With KMM, you can share business logic across platforms while still building platform-specific user interfaces. In this article, we’ll explore the benefits of KMM, its architecture, and provide code snippets to get you started with cross-platform mobile development.

Why Use Kotlin Multiplatform Mobile?

KMM enables developers to save time and resources by reusing code across mobile platforms. The shared codebase typically includes business logic, data management, and networking, while UI elements remain native to the platform. Here’s why you should consider KMM:

• Code Reusability: Share most of your app’s codebase across iOS and Android.
• Maintain Native Performance: Native UI and performance for each platform.
• Easy Integration: KMM integrates seamlessly with existing Android and iOS projects.

Setting Up a KMM Project

To get started with KMM, you can use the official Kotlin plugin in Android Studio. After setting up the project, KMM creates separate modules for shared and platform-specific code. Here’s how you can structure a simple KMM project:

// Shared module - commonMain
expect fun getPlatformName(): String

// Android module - androidMain
actual fun getPlatformName(): String {
    return "Android"
}

// iOS module - iosMain
actual fun getPlatformName(): String {
    return "iOS"
}

This structure allows you to write platform-specific implementations while sharing most of your codebase. In this example, you can call getPlatformName() from the shared module and receive a platform-specific response based on whether the app is running on Android or iOS.

Sharing Business Logic in KMM

One of the key advantages of KMM is its ability to share business logic, such as network requests, data storage, and API handling. Here’s a simple example of how you can handle network requests in the shared code:

class ApiService {
    fun fetchData(): String {
        // Placeholder for actual network call
        return "Data fetched from API"
    }
}

// Shared code usage
val apiService = ApiService()
val result = apiService.fetchData()

This code is shared between both iOS and Android, meaning you only need to write your networking logic once, reducing the time spent on maintaining platform-specific code.

Handling Dependencies with Koin in KMM

KMM supports popular Kotlin libraries like Koin for dependency injection, allowing you to manage dependencies in both shared and platform-specific code. Here’s how you can set up Koin in a KMM project:

// Shared module
val sharedModule = module {
    single { ApiService() }
}

// Android module
val androidModule = module {
    // Android-specific dependencies
}

// iOS module
val iosModule = module {
    // iOS-specific dependencies
}

By using Koin, you can define your dependencies in one place and ensure that the correct services are injected across both platforms, making your code more modular and maintainable.

Platform-Specific UI in KMM

While KMM allows you to share business logic, the user interface is still developed natively for each platform. This means you can create highly performant UIs that adhere to platform guidelines. However, you can easily pass shared data to your platform-specific UI components. Here’s a simple example of how to use shared logic in Android:

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val platformName = getPlatformName()
        findViewById<TextView>(R.id.platformTextView).text = platformName
    }
}

Similarly, you can use shared logic in Swift for iOS while keeping the UI native to iOS:

import UIKit
import shared

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()

        let platformName = CommonKt.getPlatformName()
        platformLabel.text = platformName
    }
}

In this way, KMM allows you to maintain a balance between code sharing and platform-native performance.

Conclusion: Embracing Cross-Platform Development with KMM

Kotlin Multiplatform Mobile offers developers a flexible and efficient way to build cross-platform apps without sacrificing performance or user experience. With shared business logic and platform-specific UIs, you can reduce development time and deliver high-quality apps on both Android and iOS. Start exploring KMM today to unlock the future of cross-platform development!

Source: Kotlin Multiplatform Mobile Guide