Kotlin Multiplatform for Mobile: A Beginner-Friendly Guide

In the world of mobile development, creating apps for both Android and iOS can often be time-consuming and resource-heavy. Traditionally, developers would need to write separate codebases for each platform — one for Android (in Kotlin or Java) and one for iOS (in Swift or Objective-C). However, Kotlin Multiplatform (KMP) aims to simplify this by allowing developers to share common code across multiple platforms.

In this blog, we’ll explore Kotlin Multiplatform, how it works for mobile development, how to set up a KMP project, and why it’s considered a game-changer for the future of mobile development.

What is Kotlin Multiplatform (KMP)?

Kotlin Multiplatform is a feature from JetBrains (the creators of Kotlin) that allows developers to write common code that can be shared across multiple platforms (Android, iOS, Web, Desktop). It doesn’t try to replace platform-specific code but allows you to write shared logic (such as business logic, networking, or data storage) while keeping the flexibility to write platform-specific UI or native features separately.

KMP works on the principle of writing a shared codebase for the business logic, algorithms, and data handling while letting you write specific code for each platform (like the UI or platform APIs).

Benefits of Using Kotlin Multiplatform for Mobile

1. Code Sharing: You can write common code once and use it for both Android and iOS, which saves time and reduces duplication.
2. Cross-platform Compatibility: Support for Android, iOS, Web, and even Desktop apps from a single codebase.
3. Native Performance: Since KMP compiles to native code, it offers the same performance benefits as native Android or iOS development.

How Does Kotlin Multiplatform Work?

Kotlin Multiplatform divides your project into shared code and platform-specific code.

• Shared Code: This is where you write common logic that will be used by both Android and iOS apps. This could include networking code, data manipulation, or business logic. Kotlin has libraries like kotlinx.coroutines and Ktor that work in multiplatform projects, making it easier to write asynchronous code and HTTP clients.
• Platform-specific Code: Here, you can write platform-specific implementations for things like user interfaces (UI) or platform APIs (e.g., accessing GPS, camera, or Bluetooth).

With this approach, you have the best of both worlds: shared business logic and full control over the UI and platform-specific features.

Setting Up a Kotlin Multiplatform Project

Let’s walk through the steps to set up a basic Kotlin Multiplatform project for mobile development.

Prerequisites:

• Android Studio (Arctic Fox or higher) with the Kotlin plugin installed
• Xcode (for iOS development)
• JDK (Java Development Kit)

Step-by-step Guide:

1. Create a New Project:

• Open Android Studio and click File > New Project.
• Choose Kotlin Multiplatform Mobile App from the project templates.
• Give your project a name and specify the location.

2. Project Structure: After the project is created, you’ll notice two main parts:

• Shared Module: The code written here can be used by both Android and iOS apps.
• Platform-specific Modules (Android/iOS): These are for Android and iOS-specific implementations.

3. Add Dependencies: In the shared module’s build.gradle.kts, add dependencies for the libraries you need, such as kotlinx.coroutines or Ktor.

kotlin {
    sourceSets {
        val commonMain by getting {
            dependencies {
                implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.5.2")
                implementation("io.ktor:ktor-client-core:1.6.3")
            }
        }
        val androidMain by getting
        val iosMain by getting
    }
}        

4. Writing Shared Code: You can write shared code in the commonMain source set. This could be business logic, API requests, or data handling that doesn’t depend on the platform.

expect fun platformName(): String

fun getGreeting(): String = "Hello from ${platformName()}"        

Here, expect is used to declare platform-specific functions, which you’ll implement separately for Android and iOS.

5. Platform-specific Implementations: In the androidMain and iosMain source sets, you implement the platformName function for each platform.

For Android:

actual fun platformName(): String = "Android"        

For iOS:

actual fun platformName(): String = "iOS"        

6. Running the Project:

• For Android: You can run the app as usual on an Android device or emulator.
• For iOS: Open the iOS project in Xcode (found in iosApp), and run it on an iOS device or simulator.

The Future of Kotlin Multiplatform

Kotlin Multiplatform is still evolving, but its potential is massive. JetBrains and the Kotlin community are actively working on making KMP more stable, efficient, and user-friendly.

Here’s what makes KMP a strong contender for the future of mobile development:

1. Rapid Adoption: Big companies like Netflix, Cash App, and Philips have already adopted KMP, showing its viability in production environments.
2. Growing Ecosystem: With more libraries and tools becoming multiplatform-ready (e.g., Ktor for networking, SQLDelight for databases), developing full-featured apps using KMP is becoming easier.
3. Flexibility: KMP doesn’t force you to adopt a new way of working or use non-native components. You can use as much or as little of KMP as you want, making it easier to integrate into existing projects.

Google Announced Official Kotlin Multiplatform Support

When Google announced official support for Kotlin Multiplatform (KMP) on Android during Google I/O 2024, it signaled a major shift in how developers could approach cross-platform mobile development. Kotlin Multiplatform was already widely appreciated, but Google’s backing adds credibility and momentum to this technology. With Google’s endorsement, developers can now confidently adopt KMP for projects where Android and iOS code sharing is a priority.

Here are some key points from this announcement:

• Closer Integration with Android Tools: With Google’s official support, KMP will likely have tighter integration with Android Studio and other developer tools, making the development process smoother.
• Jetpack Libraries Support: Over time, we can expect more Jetpack libraries to natively support KMP, further facilitating cross-platform development between Android and iOS.

Why Does Google’s Endorsement Matter?

Google’s endorsement essentially means that KMP is no longer just an experimental feature — it is becoming a mainstream solution. Developers, especially those working in companies, can now feel more confident in adopting KMP for production environments, knowing that Google is actively working to make it more reliable and integrated into the Android ecosystem.

Conclusion

Kotlin Multiplatform offers a powerful and flexible way to develop mobile apps for both Android and iOS with a shared codebase. By focusing on shared business logic and leaving platform-specific code to each platform’s native tools, KMP strikes a balance between efficiency and flexibility. As its ecosystem grows, Kotlin Multiplatform could become the standard approach for cross-platform mobile development in the future.

If you’re looking to streamline your mobile development process while maintaining performance and flexibility, Kotlin Multiplatform is worth exploring!

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