Hi, have you met Kotlin Multiplatform? | Kotlin User Group Berlin

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. Marco Gomiero @marcoGomier 👨💻 Senior Android Developer @ Airalo Google Developer Expert for Kotlin Hi, have you met Kotlin Multiplatform?
2. @marcoGomier https://www.youtube.com/watch?v=ddcZnW1HKUY
3. @marcoGomier “Classic” Cross Platform Solutions • All-in approach • Everything is shared, UI included • Different platforms have different patterns
4. @marcoGomier Kotlin Multiplatform • Incremental approach • You choose what to share (even UI, if you want)
5. @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
6. @marcoGomier Common Kotlin Kotlin/JVM Kotlin/JS Kotlin/Native JVM Android Browser NodeJS iOS macOS watchOS tvOS Linux Windows Mobile Kotlin/Wasm Browser Alpha
7. @marcoGomier Common and Platform-specific code • Write regular Kotlin code in the common source set • Platform-specific code goes into platform source sets
8. @marcoGomier Platform-specific code • Expect/Actual
9. @marcoGomier Expect/Actual https://kotlinlang.org/docs/multiplatform-connect-to-apis.html
10. @marcoGomier Expect/Actual expect fun debugLog(tag: String, message: String)
11. @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) } }
12. @marcoGomier Platform-specific code • Expect/Actual • Interfaces
13. @marcoGomier internal interface XmlFetcher { suspend fun fetchXml(url: String): ParserInput } Interface
14. @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 -> ... } }
15. @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? }
16. @marcoGomier Platform-specific code • Expect/Actual • Interfaces • Prefer interfaces, if possible
17. @marcoGomier How it works?
18. @marcoGomier shared androidApp iosApp Library Library iOS Android
19. @marcoGomier shared androidApp Library Android
20. @marcoGomier shared androidApp .aar/Gradle module Android Just “regular” Kotlin code, like yet another library
21. @marcoGomier shared androidApp iosApp .aar/Gradle Module Library iOS Android
22. @marcoGomier shared iosApp Library iOS
23. @marcoGomier shared iosApp Framework iOS
24. @marcoGomier XCFramework https://developer.apple.com/documentation/xcode/creating-a-multi-platform-binary-framework-bundle
25. @marcoGomier NEW https://devstreaming-cdn.apple.com/videos/wwdc/2019/416h8485aty341c2/416/416_binary_frameworks_in_swift.pdf
26. @marcoGomier https://devstreaming-cdn.apple.com/videos/wwdc/2019/416h8485aty341c2/416/416_binary_frameworks_in_swift.pdf NEW iOS mac OS watch OS tvOS
27. @marcoGomier shared iosApp Framework iOS Kotlin Objective-C Swift -> ->
28. @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 ... } }
29. @marcoGomier Some gotchas • No namespaces • No default parameters • Enums are not Swift-friendly (no values) • Sealed classes are simple classes • Coroutines without cancellation • Flows
30. @marcoGomier https://github.com/rickclephas/KMP-NativeCoroutines
31. @marcoGomier https://github.com/touchlab/SKIE
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 CocoaPods integration https://kotlinlang.org/docs/reference/native/cocoapods.html Pod::Spec.new do |spec| spec.name = 'shared' spec.version = '1.0' spec.homepage = 'Link to the Shared Module homepage' spec.source = { :http=> ''} spec.authors = '' spec.license = '' spec.summary = 'Some description for the Shared Module' spec.vendored_frameworks = 'build/cocoapods/framework/shared.framework' spec.libraries = 'c++' spec.ios.deployment_target = '14.1' spec.pod_target_xcconfig = { 'KOTLIN_PROJECT_PATH' => ':shared', 'PRODUCT_MODULE_NAME' => 'shared', } spec.script_phases = [ { :name => 'Build shared', :execution_position => :before_compile, :shell_path => '/bin/sh', :script => <<-SCRIPT if [ "YES" = "$OVERRIDE_KOTLIN_BUILD_IDE_SUPPORTED" ]; then echo "Skipping Gradle build task invocation due to OVERRIDE_KOTLIN_BUILD_IDE_SUPPORTED environment exit 0 fi set -ev REPO_ROOT="$PODS_TARGET_SRCROOT" "$REPO_ROOT/../gradlew" -p "$REPO_ROOT" $KOTLIN_PROJECT_PATH:syncFramework \ -Pkotlin.native.cocoapods.platform=$PLATFORM_NAME \ -Pkotlin.native.cocoapods.archs="$ARCHS" \ -Pkotlin.native.cocoapods.configuration="$CONFIGURATION" SCRIPT } ] end
45. @marcoGomier iOSApp: Podfile https://kotlinlang.org/docs/reference/native/cocoapods.html target 'iosApp' do use_frameworks! platform :ios, '14.1' pod 'shared', :path => '../shared' end
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
54. @marcoGomier Common Kotlin Android App iOS App .aar XCFramework
55. @marcoGomier Common Kotlin Android App iOS App .aar XCFramework Android App Repository KMP Repository iOs App Repository
56. @marcoGomier https://terrakok.github.io/kmp-web-wizard/
57. @marcoGomier How to publish: Android
58. @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") } } }
59. @marcoGomier Publish the artifacts ./gradlew publish
60. @marcoGomier Publish the artifacts ./gradlew publish ./gradlew publishToMavenLocal
61. @marcoGomier How to publish: iOS
62. @marcoGomier 🥵
63. @marcoGomier XCFramework
64. @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 } } }
65. @marcoGomier XCFramework: Gradle tasks assemble${libName}XCFramework assemble${libName}DebugXCFramework assemble${libName}ReleaseXCFramework
66. @marcoGomier Build an XCFramework
67. @marcoGomier https://github.com/touchlab/KMMBridge
68. @marcoGomier https://github.com/touchlab/KMMBridge
69. @marcoGomier https://github.com/prof18/kmp-framework-bundler
70. @marcoGomier Where to start
71. @marcoGomier shared androidApp iosApp Gradle Module Framework Same Repository New projects
72. @marcoGomier 🧑🎨 You have a blank canvas
73. @marcoGomier Existing projects Common Kotlin Android App iOS App .aar XCFramework Android App Repository KMP Repository iOs App Repository
74. @marcoGomier 💡 Create a library!
75. @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?
76. @marcoGomier • DTOs • Common Models • Utility methods • Analytics • . . . Where to start?
77. @marcoGomier Start little
78. @marcoGomier Start little Go bigger then
79. @marcoGomier Start little then go bigger • Validate the process with “little” effort • Then you can go bigger and share more “features”
80. @marcoGomier Ecosystem
81. @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
82. @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 ...
83. @marcoGomier https://github.com/AAkira/Kotlin-Multiplatform-Libraries https://github.com/terrakok/kmp-awesome
84. @marcoGomier https://github.com/touchlab/xcode-kotlin
85. @marcoGomier https://github.com/touchlab/xcode-kotlin
86. @marcoGomier https://github.com/touchlab/xcode-kotlin
87. @marcoGomier https://www.jetbrains.com/ fl eet/
88. @marcoGomier https://github.com/touchlab/CrashKiOS
89. @marcoGomier https://github.com/touchlab/CrashKiOS
90. @marcoGomier Conclusions
91. @marcoGomier • Kotlin Multiplatform ! = Cross Platform • Stable since Kotlin 1.9.20 • It’s a joint and team approach Conclusions
92. 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: / / www.droidcon.com/2023/07/31/10-myths-about-crossplatform-mobile-development-with-kotlin/ • https: / / blog.jetbrains.com/kotlin/2023/11/kotlin-multiplatform-stable/
93. @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