Introducing Kotlin Multiplatform in an existing mobile app - Workshop Edition | DevFest Hamburg

After discovering a new interesting technology or framework, you will probably start asking yourself how to integrate it into an existing project. That's because, the possibility of starting with a blank canvas is rare (not impossible, but rare).

This is also the case for Kotlin Multiplatform, which is getting more and more hype every day. And now, that the technology has become stable, it's the perfect time to start using it! In this hands-on session, we will start with an existing Android and iOS application that "lives" in separate repositories, we will extract the business logic from the Android app and share it between the two apps with a Kotlin Multiplatform library. We will also cover how to distribute the library to the existing applications. By the end of this workshop, you'll have a better understanding of what is needed to start using Kotlin Multiplatform in your existing projects.

Transcript

1. @marcoGomier Marco Gomiero Senior Android Developer @ Airalo Google Developer Expert for Kotlin Introducing Kotlin Multiplatform in an existing mobile app workshop edition
2. @marcoGomier Prerequisites • Download Android Studio and the Kotlin Multiplatform Plugin • Download Xcode • A valid GitHub account. You can check if your system is ready for Kotlin Multiplatform with kdoctor: https: // github.com/Kotlin/kdoctor
3. @marcoGomier bit.ly/kmp-existing-app-workshop
4. @marcoGomier Agenda • Quick intro about Kotlin Multiplatform • Start from an Android and iOS native app - that lives in separate repositories and extract the business logic from Android into a new KMP library • Deploy the library on Android • Break ☕ • Deploy the library on iOS • How to deploy in a scalable way • iOS API enhancements
5. @marcoGomier What is Kotlin Multiplatform?
6. @marcoGomier “Classic” Cross Platform Solutions • All-in approach • Everything is shared, UI included • Different platforms have different patterns
7. @marcoGomier Kotlin Multiplatform • Incremental approach • You choose what to share (even UI, if you want)
8. @marcoGomier Photo by Erwan Hesry on Unsplash 💡 Create a library!
9. @marcoGomier Common Kotlin Kotlin/JVM Kotlin/JS Kotlin/Native JVM Android Browser NodeJS iOS macOS watchOS tvOS Linux Windows Supported Platforms Kotlin/Wasm Browser Alpha
10. @marcoGomier Common Kotlin Kotlin/JVM Kotlin/JS Kotlin/Native JVM Android Browser NodeJS iOS macOS watchOS tvOS Linux Windows Mobile Kotlin/Wasm Browser Alpha
11. @marcoGomier How it works?
12. @marcoGomier shared androidApp iosApp Library Library iOS Android
13. @marcoGomier shared androidApp Gradle Module Android Same repository
14. @marcoGomier shared androidApp .aar Android Different repositories
15. @marcoGomier iosApp iOS shared XCFramework Different repositories Same repository
16. @marcoGomier XCFramework https://developer.apple.com/documentation/xcode/creating-a-multi-platform-binary-framework-bundle
17. @marcoGomier NEW https://devstreaming-cdn.apple.com/videos/wwdc/2019/416h8485aty341c2/416/416_binary_frameworks_in_swift.pdf
18. @marcoGomier https://devstreaming-cdn.apple.com/videos/wwdc/2019/416h8485aty341c2/416/416_binary_frameworks_in_swift.pdf NEW iOS mac OS watch OS tvOS
19. @marcoGomier shared androidApp iosApp Gradle Module XCFramework Same Repository Easier for new projects
20. @marcoGomier Common Kotlin Android App iOS App .aar XCFramework Android App Repository KMP Repository iOS App Repository Easier for existing projects
21. @marcoGomier Code Time 🧑💻
22. @marcoGomier bit.ly/kmp-existing-workshop
23. @marcoGomier XCFramework https://developer.apple.com/documentation/xcode/creating-a-multi-platform-binary-framework-bundle
24. @marcoGomier iOS Dependency Managers • CocoaPods • Carthage • Swift Package Manager 💀 💀 ✅
25. @marcoGomier Swift Package Manager • Based on git • Configured with a Package.swift file • Semantic versioning (e.g. 1.2.3) with git tags • Can contain code or binaries • Can be local or remote, it’s git!
26. @marcoGomier Code Time 🧑💻
27. @marcoGomier Swift Package Manager https://twitter.com/kpgalligan/status/1723364386046173493
28. @marcoGomier Code Time 🧑💻
29. @marcoGomier shared iosApp Framework iOS Kotlin Objective-C Swift -> ->
30. @marcoGomier Some gotchas • No namespaces • No default parameters • Enums are not Swift-friendly (no values) • Sealed classes are simple classes • Coroutines without cancellation • Flows
31. @marcoGomier https://github.com/JetBrains/kotlin/tree/master/docs/swift-export
32. @marcoGomier Code Time 🧑💻
33. @marcoGomier Conclusions • You choose what to share (even UI, if you want) • Validate the process with “little” effort • Find the best (for you) approach/infrastructure • Then you can go bigger and share more “features”
34. @marcoGomier https://touchlab.co/kmp-teams-use-source More reading
35. Bibliography / Useful Links • https: // docs.github.com/en/actions/publishing-packages/publishing-java-packages-with-gradle • https: // github.com/orgs/community/discussions/26328#discussioncomment-3251485 • https: // github.com/orgs/community/discussions/26634 • https: // developer.apple.com/documentation/xcode/creating-a-multi-platform-binary-framework-bundle • https: // devstreaming-cdn.apple.com/videos/wwdc/2019/416h8485aty341c2/416/416_binary_frameworks_in_swift.pdf • https: // kotlinlang.org/docs/multiplatform-build-native-binaries.html • https: // developer.apple.com/documentation/xcode/distributing-binary-frameworks-as-swift-packages • https: // github.com/rickclephas/KMP-NativeCoroutines • https: // skie.touchlab.co/ • https: // touchlab.co/skie-migration?ti=4B0F129C5D944E54B60B31FE35 • https: // kotlinlang.org/docs/native-objc-interop.html • https: // kotlinlang.org/docs/apple-framework.html • https: // github.com/kotlin-hands-on/kotlin-swift-interopedia • https: // medium.com/@aoriani/list/writing-swiftfriendly-kotlin-multiplatform-apis-c51c2b317fce • https: // blog.devgenius.io/dependancy-management-for-ios-27dd681d7ea0 • https: // github.com/luca992/multiplatform-swiftpackage • https: // touchlab.co/kmmbridge/ • https: // touchlab.co/kmmbridge/spmquickstart • https: // medium.com/geekculture/xcode-13-3-supports-spm-binary-dependency-in-private-github-release-8d60a47d5e45 • https: // touchlab.co/xcodekotlin • https: // kotlinlang.org/docs/native-spm.html#swift-package-distribution • https: // github.com/JetBrains/kotlin/tree/master/docs/swift-export • https: // github.com/Kotlin/swift-export-sample
36. @marcoGomier Thank you! > Twitter: @marcoGomier > Github: prof18 > Website: marcogomiero.com > Mastodon: androiddev.social/@marcogom Marco Gomiero Senior Android Developer @ Airalo Google Developer Expert for Kotlin