Hello to all the coding enthusiasts out there! Are you curious about how to migrate your Android app written in Kotlin to an iOS app? Well, you've come to the right place! In today's blog post, we'll explore the pathway to achieving just that, with the help of Kotlin Multiplatform Mobile (KMM).

Introduction to Kotlin Multiplatform Mobile

Kotlin Multiplatform Mobile (KMM) is a SDK provided by JetBrains, the creators of Kotlin. KMM aims to allow developers to use the same business logic code in both iOS and Android applications, thereby increasing efficiency and reducing time and effort. With KMM, you write the business logic in Kotlin, which then can be used on both Android (JVM) and iOS (Native).

Let's delve into the specifics on how to transform your Android app into an iOS one using KMM.

Migrating Shared Logic to KMM

The first step in the conversion process involves extracting the shared logic from your Android application and placing it into a KMM shared module. This typically includes the business logic and data layers, and the goal is to allow this code to be shared by both platforms.

To do this, you create a new KMM shared module in your Android Studio project, then move the common code into it. Here's an example of how to define a simple model class in a KMM shared module:

kotlin

expect class Platform() {
    val platform: String
}

class Sample {
    fun checkPlatform(): String {
        val platform = Platform().platform
        return "Running on $platform"
    }
}

In the above code, the expect keyword is used to declare a placeholder for platform-specific implementations.

Next, you would provide the actual implementations for Android and iOS. Here's how:

kotlin

// Android
actual class Platform actual constructor() {
    actual val platform: String = "Android ${android.os.Build.VERSION.SDK_INT}"
}

// iOS
actual class Platform actual constructor() {
    actual val platform: String = "iOS ${UIDevice.currentDevice.systemVersion}"
}

Developing the iOS Application

After you've migrated the shared logic into the KMM module, the next step is to create an iOS application. For this, you will use Xcode, Apple's IDE for developing iOS applications.

Once you've set up your iOS project in Xcode, you can import the shared KMM module. The KMM plugin for Android Studio supports building a framework for iOS which you can then use in Xcode. This is a .framework file that you can simply drag and drop into your Xcode project.

Within your iOS app, you can then reference and use the shared Kotlin code like any other Swift or Objective-C code. Here's an example:

swift

import SharedCode

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        let sample = Sample()
        label.text = sample.checkPlatform()
    }
}

In this example, SharedCode is the KMM module, and Sample is the Kotlin class defined in the shared module.

Testing and Deployment

After the iOS app is developed, ensure that you thoroughly test the application, just like you would with your Android app. Remember, even though the business logic code is the same for both platforms, the UI and UX can be quite different. Make sure to follow Apple's Human Interface Guidelines to create an intuitive and platform-consistent user interface.

Once testing is completed, you can then deploy your iOS app to the App Store.

Conclusion

Kotlin Multiplatform Mobile is a powerful tool that can help you leverage your Kotlin Android app codebase and extend it to iOS. Although KMM is still experimental as of my last training cut-off in September 2021, it has been adopted by several major companies and has demonstrated success in real-world applications.

Remember, while KMM facilitates sharing of business logic code, the UI still needs to be developed separately for each platform. This approach ensures that each app maintains the look and feel of its respective platform, thereby providing the best user experience.

We hope this blog post helps you in your journey from a Kotlin Android app to an iOS app. Happy coding!