FAQ

What is Kotlin Multiplatform?

Kotlin Multiplatform (KMP) is an open-source technology by JetBrains for flexible cross-platform development. It allows you to create applications for various platforms and efficiently reuse code across them while retaining the benefits of native programming. With Kotlin Multiplatform, you can develop apps for Android, iOS, desktop, web, server-side, and other platforms.

Can I share UIs with Kotlin Multiplatform?

Yes, you can share UIs using Compose Multiplatform, JetBrains' declarative UI framework based on Kotlin and Jetpack Compose. This framework allows you to create shared UI components for platforms like iOS, Android, desktop, and web, helping you to maintain a consistent user interface across different devices and platforms.

To learn more, see the Compose Multiplatform section.

What platforms does Kotlin Multiplatform support?

Kotlin Multiplatform supports Android, iOS, desktop, web, server-side, and other platforms. Learn more about supported platforms.

In which IDE should I work on my cross-platform app?

We recommend using JetBrains Fleet or Android Studio, depending on your project needs and expectations. Learn more about which one to choose in Recommended IDEs.

How do I create a new Kotlin Multiplatform project?

The Get started with Kotlin Multiplatform tutorial provides step-by-step instructions for creating Kotlin Multiplatform projects. You can decide what to share – only logic or both logic and a UI.

I have an existing Android application. How can I migrate it to Kotlin Multiplatform?

The Make your Android application work on iOS step-by-step tutorial explains how to make your Android application work on iOS with a native UI. If you also want to share the UI with Compose Multiplatform, see the corresponding answer.

Where can I get complete examples to play with?

Here's a list of real-life examples.

Where can I find a list of real-life Kotlin Multiplatform applications? What companies use KMP in production?

Check out our list of case studies to learn from other companies that have already adopted Kotlin Multiplatform in production.

Which operating systems can work with Kotlin Multiplatform?

If you are going to work with shared code or platform-specific code, except for iOS, you can work on any operating system supported by your IDE.

Learn more about recommended IDEs.

If you want to write iOS-specific code and run an iOS application on a simulator or real device, use a Mac with a macOS. This is because iOS simulators can run only on macOS, per Apple requirements, but cannot run on other operating systems, such as Microsoft Windows or Linux.

How can I write concurrent code in Kotlin Multiplatform projects?

You can still use coroutines and flows to write asynchronous code in your Kotlin Multiplatform projects. How you call this code depends on where you call the code from. Calling suspending functions and flows from Kotlin code is widely documented, especially for Android. Calling them from Swift code requires a little more work, see KT-47610 for more details.

The best current approach for calling suspending functions and flows from Swift is to use plugins and libraries like KMP-NativeCoroutines or SKIE together with Swift's async/await or libraries like Combine and RxSwift. At the moment, KMP-NativeCoroutines is the more tried-and-tested solution, and it supports async/await, Combine, and RxSwift approaches to concurrency. SKIE is easier to set up and less verbose. For instance, it maps Kotlin Flow to Swift AsyncSequence directly. Both of these libraries support the proper cancellation of coroutines.

To learn how to use them, see Share more logic between iOS and Android.

What is Kotlin/Native, and how does it relate to Kotlin Multiplatform?

Kotlin/Native is a technology for compiling Kotlin code to native binaries, which can run without a virtual machine. It includes an LLVM-based backend for the Kotlin compiler and a native implementation of the Kotlin standard library.

Kotlin/Native is primarily designed to allow compilation for platforms where virtual machines are not desirable or possible, such as embedded devices and iOS. It is particularly suitable when you need to produce a self-contained program that does not require an additional runtime or virtual machine.

For example, in mobile applications, shared code written in Kotlin is compiled to JVM bytecode for Android with Kotlin/JVM and compiled to native binaries for iOS with Kotlin/Native. It makes the integration with Kotlin Multiplatform seamless on both platforms.

How can I speed up my Kotlin Multiplatform module compilation for native platforms (iOS, macOS, Linux)?

See these tips for improving Kotlin/Native compilation times.

What is Compose Multiplatform?

Compose Multiplatform is a modern declarative and reactive UI framework developed by JetBrains that provides a simple way to build user interfaces with a small amount of Kotlin code. It also allows you to write your UI once and run it on any of the supported platforms – iOS, Android, desktop (Windows, macOS, Linux), and web.

How does it relate to Jetpack Compose for Android?

Compose Multiplatform shares most of its API with Jetpack Compose, the Android UI framework developed by Google. In fact, when you are using Compose Multiplatform to target Android, your app simply runs on Jetpack Compose. Other platforms targeted by Compose Multiplatform may have implementation details under the hood that differ from those of Jetpack Compose on Android, but they still provide you with the same APIs.

Between which platforms can I share my UI?

We want you to have the option to share your UI between any combination of popular platforms – Android, iOS, desktop ( Linux, macOS, Windows), and web (based on Wasm). However, Compose Multiplatform is only Stable for Android and desktop at the moment. For more details, see Supported platforms.

Can I use Compose Multiplatform in production?

The Android and desktop targets of Compose Multiplatform are Stable. You can use them in production. The iOS target is in Alpha, which means that it's in active development. You can use it with caution and expect migration issues. The version of Compose Multiplatform for web that is based on WebAssembly is Experimental. You can try it in your pet projects. It has the same UI as Compose Multiplatform for iOS, Android, and desktop.

How do I create a new Compose Multiplatform project?

The Get started with Compose Multiplatform tutorial provides step-by-step instructions for creating a Kotlin Multiplatform project with Compose Multiplatform for Android, iOS, and desktop. You can also watch a video tutorial on YouTube created by Kotlin Developer Advocate Sebastian Aigner.

What IDE should I use for building apps with Compose Multiplatform?

We recommend using JetBrains Fleet or Android Studio, depending on your project needs and expectations. To try a new multiplatform experience without juggling different IDEs and switching to Xcode for writing Swift code, try out JetBrains Fleet tutorial.

For more details on which one to choose, see Recommended IDEs.

Can I play with a demo application? Where can I find it?

You can play with our samples.

Does Compose Multiplatform come with widgets?

Yes, Compose Multiplatform provides full support for Material 3 widgets.

To what extent can I customize the appearance of Material widgets?

You can use Material's theming capabilities to customize colors, fonts, and paddings. If you want to create a unique design, you can create custom widgets and layouts.

Can I share the UI in my existing Kotlin Multiplatform app?

If your application uses a native API for its UI (which is the most common case), you can gradually rewrite some parts to Compose Multiplatform, as it provides interoperability for that. You can replace native UIs with a special interop view that wraps a common UI written with Compose.

I have an existing Android application that uses Jetpack Compose. What should I do to migrate it to other platforms?

Migration of the app consists of two parts: migrating the UI and migrating the logic. The complexity of the migration depends on the complexity of your application and the amount of Android-specific libraries you use. You can migrate most of your screens to Compose Multiplatform without changes. All of the Jetpack Compose widgets are supported. However, some APIs work only in the Android target – they might be Android-specific or have yet to be ported to other platforms. For instance, resource handling is Android-specific, so you would need to migrate to the Compose Multiplatform resource library or use a community solution. The Android Navigation library is also Android-specific, but there are community alternatives available. For more information on components available only for Android, see the current list of Android-only APIs.

You need to migrate the business logic to Kotlin Multiplatform. When you try to move your code to shared modules, the parts that use Android dependencies stop compiling, and you need to rewrite them.

• You can rewrite the code that uses Android-only dependencies to use multiplatform libraries instead. Some libraries might already support Kotlin Multiplatform, so no changes are needed. You can check the KMP-awesome library list.

• Alternatively, you can separate common code from platform-specific logic and provide common interfaces that are implemented differently depending on the platform. On Android, the implementation can use your existing functionality, and on other platforms, such as iOS, you need to provide new implementations for the common interfaces.

Can I integrate Compose screens into an existing iOS app?

Yes. Compose Multiplatform supports different integration scenarios. For more information on integration with iOS UI frameworks, see Integration with SwiftUI and Integration with UIKit.

Can I integrate UIKit or SwiftUI components into a Compose screen?

Yes, you can. See Integration with SwiftUI and Integration with UIKit.

What happens when my mobile OS updates and changes the visual style of the system components or their behavior?

Your UI will stay the same after the OS updates because all of the components are drawn on a canvas. If you embed native iOS components into your screen, updates may affect their appearance.

What are the plans for the Kotlin Multiplatform evolution?

We at JetBrains are investing much to provide the best experience for multiplatform development and eliminate existing pains of multiplatform users. We have plans for improving the core Kotlin Multiplatform technology, integration with the Apple ecosystem, tooling, and our Compose Multiplatform UI framework. Check out our roadmap.

When will Compose Multiplatform become Stable?

Compose Multiplatform is Stable for Android and desktop, while the iOS platform support is in Alpha, and web is Experimental.

We are planning to promote Compose Multiplatform for iOS to Beta and Compose Multiplatform for web to Alpha in 2024. There are no specific dates for stabilizing support for these platforms. For more information on stability statuses, see Supported platforms.

What about future support for web targets in Kotlin and Compose Multiplatform?

We're currently focusing resources on WebAssembly (Wasm), which shows great potential. You can experiment with our new Kotlin/Wasm backend and Compose Multiplatform for web powered by Wasm.

As for the JS target, the Kotlin/JS backend has already reached Stable status. In Compose Multiplatform, due to resource constraints, we've shifted our focus from JS Canvas to Wasm, which we believe holds more promise.

We also offer Compose HTML, previously known as Compose Multiplatform for web. It's an additional library designed for working with the DOM in Kotlin/JS, and it's not intended for sharing UIs across platforms.

Are there any plans to improve tooling for multiplatform development?

Yes, we're acutely aware of the current challenges with multiplatform tooling and are actively working on enhancements in several areas.

We've already launched previews of the Kotlin Multiplatform support in Fleet. Try it yourself and leave feedback!

Are you going to provide a Swift interop?

Yes. We're currently investigating various approaches to provide direct interoperability with Swift, with a focus on exporting Kotlin code to Swift.