Hi, have you met Kotlin Multiplatform? | DevFest Vienna 2024

Kotlin Multiplatform is getting more and more hype every day. It started as an experimental technology, then alpha, beta, and now it's finally stable.

We constantly read of new companies and teams that are using KMP for experiments and production projects alike. And we're left wondering: why pick KMP over any other cross-platform solution? How to approach it? And, most importantly, is it possible to start using it in existing projects?

In this talk, I'll answer these questions, clarifying all the doubts and making you ready to use and love Kotlin Multiplatform.

Transcript

1. @marcoGomier Marco Gomiero Senior Android Developer @ Airalo Google Developer Expert for Kotlin Hi, have you met Kotlin Multiplatform?
2. @marcoGomier “Classic” Cross Platform Solutions • All-in approach • Everything is shared, UI included • Different platforms have different patterns
3. @marcoGomier Kotlin Multiplatform • Incremental approach • You choose what to share (even UI, if you want)
4. @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
5. @marcoGomier Common Kotlin Kotlin/JVM Kotlin/JS Kotlin/Native JVM Android Browser NodeJS iOS macOS watchOS tvOS Linux Windows Mobile Kotlin/Wasm Browser Alpha
6. @marcoGomier Common and Platform-specific code • Write regular Kotlin code in the common source set • Platform-specific code goes into platform source sets
7. @marcoGomier Platform-specific code • Expect/Actual
8. @marcoGomier Expect/Actual https://kotlinlang.org/docs/multiplatform-connect-to-apis.html
9. @marcoGomier Expect/Actual expect fun debugLog(tag: String, message: String)
10. @marcoGomier expect fun debugLog(tag: String, message: String) import android.util.Log actual fun debugLog(tag: String, message: String) { Log.d(tag, message) } import platform.Foundation.NSLog actual fun debugLog(tag: String, message: String) { if (Platform.isDebugBinary) { NSLog("%s: %s", tag, message) } }
11. @marcoGomier Platform-specific code • Expect/Actual • Interfaces
12. @marcoGomier internal interface XmlFetcher { suspend fun fetchXml(url: String): ParserInput } Interface
13. @marcoGomier internal interface XmlFetcher { suspend fun fetchXml(url: String): ParserInput } internal class JvmXmlFetcher( private val callFactory: Call.Factory, ): XmlFetcher { override suspend fun fetchXml(url: String): ParserInput { val request = createRequest(url) return ParserInput( inputStream = callFactory.newCall(request).await() ) } } internal class IosXmlFetcher( private val nsUrlSession: NSURLSession, ): XmlFetcher { override suspend fun fetchXml(url: String): ParserInput = suspendCancellableCoroutine { continuation -> ... } }
14. @marcoGomier import org.jsoup.Jsoup internal class JvmHtmlParser : HtmlParser { override fun getTextFromHTML(html: String): String? { return try { val doc = Jsoup.parse(html) doc.text() } catch (e: Throwable) { null } } } import shared import SwiftSoup class IosHtmlParser: HtmlParser { func getTextFromHTML(html: String) -> String? { do { let doc: Document = try SwiftSoup.parse(html) return try doc.text() } catch { return nil } } } interface HtmlParser { fun getTextFromHTML(html: String): String? }
15. @marcoGomier Platform-specific code • Expect/Actual • Interfaces • Prefer interfaces, if possible
16. @marcoGomier How it works?
17. @marcoGomier shared androidApp iosApp Library Library iOS Android
18. @marcoGomier shared androidApp Library Android
19. @marcoGomier shared androidApp .aar/Gradle module Android Just “regular” Kotlin code, like yet another library
20. @marcoGomier shared androidApp iosApp .aar/Gradle Module Library iOS Android
21. @marcoGomier shared iosApp Library iOS
22. @marcoGomier shared iosApp Framework iOS
23. @marcoGomier XCFramework https://developer.apple.com/documentation/xcode/creating-a-multi-platform-binary-framework-bundle
24. @marcoGomier NEW https://devstreaming-cdn.apple.com/videos/wwdc/2019/416h8485aty341c2/416/416_binary_frameworks_in_swift.pdf
25. @marcoGomier https://devstreaming-cdn.apple.com/videos/wwdc/2019/416h8485aty341c2/416/416_binary_frameworks_in_swift.pdf NEW iOS mac OS watch OS tvOS
26. @marcoGomier shared iosApp Framework iOS Kotlin Objective-C Swift -> ->
27. @marcoGomier when (appState.newsState) { is NewsState.Loading -> { progressBar.visibility = View.VISIBLE ... } is NewsState.Error -> { errorButton.visibility = View.VISIBLE errorMessage.visibility = View.VISIBLE ... } is NewsState.Success -> { progressBar.visibility = View.GONE errorMessage.visibility = View.GONE recyclerView.visibility = View.VISIBLE ... } }
28. @marcoGomier Some gotchas • No namespaces • No default parameters • Enums are not Swift-friendly (no values) • Sealed classes are simple classes • Coroutines without cancellation • Flows
29. @marcoGomier https://github.com/rickclephas/KMP-NativeCoroutines
30. @marcoGomier https://github.com/touchlab/SKIE
31. @marcoGomier https://github.com/JetBrains/kotlin/tree/master/docs/swift-export
32. @marcoGomier Make it a team effort
33. @marcoGomier New projects
34. @marcoGomier Create a new app project
35. @marcoGomier
36. @marcoGomier
37. @marcoGomier
38. @marcoGomier shared androidApp Gradle Module Android
39. @marcoGomier // settings.gradle.kts include(":shared") // build.gradle.kts implementation(project(":shared")) Android
40. @marcoGomier shared androidApp iosApp Gradle Module Framework iOS Android
41. @marcoGomier Create a new app project
42. @marcoGomier Regular Framework
43. @marcoGomier Create a new app project
44. @marcoGomier Create a new app project Prefer the “Regular Framework”
45. @marcoGomier CocoaPods is in maintenance mode https://blog.cocoapods.org/CocoaPods-Support-Plans/
46. @marcoGomier shared androidApp iosApp Gradle Module Framework iOS Android
47. @marcoGomier shared androidApp iosApp Framework Same Repository Gradle Module
48. @marcoGomier https://kmp.jetbrains.com/#newProject
49. @marcoGomier Existing projects
50. @marcoGomier 🙅 shared androidApp iosApp Gradle Module Framework Same Repository Existing projects
51. @marcoGomier 💡 Create a library!
52. @marcoGomier Create a new library project
53. @marcoGomier Create a new KMP module in the Android App * from canary
54. @marcoGomier
55. @marcoGomier Common Kotlin Android App iOS App .aar XCFramework
56. @marcoGomier Common Kotlin Android App iOS App .aar XCFramework Android App Repository KMP Repository iOs App Repository
57. @marcoGomier https://touchlab.co/kmp-teams-use-source More reading
58. @marcoGomier https://terrakok.github.io/kmp-web-wizard/
59. @marcoGomier How to publish: Android
60. @marcoGomier Setup a Maven repository to share the artifacts: build.gradle.kts plugins { //... id("maven-publish") } group = "com.prof18.hn.foundation" version = "1.0" publishing { repositories { maven { credentials { username = "username" password = "pwd" } url = URI.create("https://mymavenrepo.it") } } }
61. @marcoGomier Publish the artifacts ./gradlew publish
62. @marcoGomier Publish the artifacts ./gradlew publish ./gradlew publishToMavenLocal
63. @marcoGomier How to publish: iOS
64. @marcoGomier 🥵
65. @marcoGomier XCFramework
66. @marcoGomier Build an XCFramework https://kotlinlang.org/docs/multiplatform-build-native-binaries.html#build-xcframeworks import org.jetbrains.kotlin.gradle.plugin.mpp.apple.XCFramework kotlin { ... val libName = "LibraryName" val xcf = XCFramework(libName) listOf( iosX64(), iosArm64(), iosSimulatorArm64() ).forEach { it.binaries.framework { baseName = libName xcf.add(this) isStatic = true } } }
67. @marcoGomier XCFramework: Gradle tasks assemble${libName}XCFramework assemble${libName}DebugXCFramework assemble${libName}ReleaseXCFramework
68. @marcoGomier Build an XCFramework
69. @marcoGomier https://github.com/touchlab/KMMBridge
70. @marcoGomier https://github.com/touchlab/KMMBridge
71. @marcoGomier Where to start
72. @marcoGomier shared androidApp iosApp Gradle Module Framework Same Repository New projects
73. @marcoGomier 🧑🎨 You have a blank canvas
74. @marcoGomier Existing projects Common Kotlin Android App iOS App .aar XCFramework Android App Repository KMP Repository iOs App Repository
75. @marcoGomier 💡 Create a library!
76. @marcoGomier • Boring code to write multiple times • Code/feature that centralizes the source of truth • Code/feature that can be gradually extracted Where to start?
77. @marcoGomier • DTOs • Common Models • Utility methods • Analytics • . . . Where to start?
78. @marcoGomier Start little then go bigger • Validate the process with “little” effort • Then you can go bigger and share more “features”
79. @marcoGomier Ecosystem
80. @marcoGomier • Networking: Ktor, Apollo • Persistence: SQLDelight, multiplatform-settings, Realm • Serialization: kotlinx.serialization • Dependency Injection: Koin, Kodein, kotlin-inject • Asynchronous: Coroutines, Reaktive • Date/Time: kotlinx-datetime • Logging: Kermit, Napier Common Libraries And much more ...
81. @marcoGomier https://github.com/AAkira/Kotlin-Multiplatform-Libraries https://github.com/terrakok/kmp-awesome
82. @marcoGomier https://github.com/touchlab/xcode-kotlin
83. @marcoGomier https://github.com/touchlab/xcode-kotlin
84. @marcoGomier https://github.com/touchlab/xcode-kotlin
85. @marcoGomier https://www.jetbrains.com/ fl eet/
86. @marcoGomier https://github.com/touchlab/CrashKiOS
87. @marcoGomier https://github.com/touchlab/CrashKiOS
88. @marcoGomier Conclusions
89. @marcoGomier https://blog.jetbrains.com/kotlin/2023/11/kotlin-multiplatform-stable/
90. @marcoGomier https://www.youtube.com/watch?v=ddcZnW1HKUY
91. @marcoGomier https://android-developers.googleblog.com/2024/05/android-support-for-kotlin-multiplatform-to-share-business-logic-across-mobile-web-server-desktop.html?m=1
92. @marcoGomier • Kotlin Multiplatform ! = Cross Platform • It’s a joint and team approach Conclusions
93. Bibliography / Useful Links • https: // kotlinlang.org/docs/multiplatform.html • https: // kotlinlang.org/docs/native-overview.html • https: // kotlinlang.org/docs/js-overview.html • https: // kotlinlang.org/docs/multiplatform-share-on-platforms.html • https: // kotlinlang.org/docs/multiplatform-connect-to-apis.html • https: // devstreaming-cdn.apple.com/videos/wwdc/2019/416h8485aty341c2/416/416_binary_frameworks_in_swift.pdf • https: // developer.apple.com/videos/play/wwdc2019/416/ • https: // medium.com/@aoriani/list/writing-swiftfriendly-kotlin-multiplatform-apis-c51c2b317fce • https: // kotlinlang.org/docs/native-objc-interop.html • https: // speakerdeck.com/kpgalligan/kotlinconf-2023-kotlin-mobile-multiplatform-for-teams • https: // speakerdeck.com/kpgalligan/sdk-design-and-publishing-for-kotlin-multiplatform-mobile • https: // kotlinlang.org/docs/reference/native/cocoapods.html • https: // kotlinlang.org/docs/multiplatform-build-native-binaries.html#build-xcframeworks • https: // github.com/touchlab/KMMBridge • https: // github.com/prof18/kmp-framework-bundler • https: // github.com/luca992/multiplatform-swiftpackage • https: // github.com/touchlab/xcode-kotlin • https: // github.com/terrakok/kmp-awesome • https: // github.com/AAkira/Kotlin-Multiplatform-Libraries • https: // github.com/touchlab/CrashKiOS • https: // blog.jetbrains.com/kotlin/2023/11/kotlin-multiplatform-stable/ • https: // github.com/JetBrains/kotlin/tree/master/docs/swift-export • https: // android-developers.googleblog.com/2024/05/android-support-for-kotlin-multiplatform-to-share-business-logic-across-mobile-web-server-desktop.html?m=1
94. @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