Hi, have you met Kotlin Multiplatform? | Appdevcon

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 “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 Make it a team effort
32. @marcoGomier New projects
33. @marcoGomier Create a new app project
34. @marcoGomier
35. @marcoGomier
36. @marcoGomier
37. @marcoGomier shared androidApp Gradle Module Android
38. @marcoGomier // settings.gradle.kts include(":shared") // build.gradle.kts implementation(project(":shared")) Android
39. @marcoGomier shared androidApp iosApp Gradle Module Framework iOS Android
40. @marcoGomier Create a new app project
41. @marcoGomier Regular Framework
42. @marcoGomier Create a new app project
43. @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
44. @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
45. @marcoGomier shared androidApp iosApp Gradle Module Framework iOS Android
46. @marcoGomier shared androidApp iosApp Framework Same Repository Gradle Module
47. @marcoGomier Existing projects
48. @marcoGomier 🙅 shared androidApp iosApp Gradle Module Framework Same Repository Existing projects
49. @marcoGomier 💡 Create a library!
50. @marcoGomier Create a new library project
51. @marcoGomier
52. @marcoGomier Common Kotlin Android App iOS App .aar XCFramework
53. @marcoGomier Common Kotlin Android App iOS App .aar XCFramework Android App Repository KMP Repository iOs App Repository
54. @marcoGomier How to publish: Android
55. @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") } } }
56. @marcoGomier Publish the artifacts ./gradlew publish
57. @marcoGomier Publish the artifacts ./gradlew publish ./gradlew publishToMavenLocal
58. @marcoGomier How to publish: iOS
59. @marcoGomier 🥵
60. @marcoGomier XCFramework
61. @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 } } }
62. @marcoGomier XCFramework: Gradle tasks assemble${libName}XCFramework assemble${libName}DebugXCFramework assemble${libName}ReleaseXCFramework
63. @marcoGomier Build an XCFramework
64. @marcoGomier https://github.com/touchlab/KMMBridge
65. @marcoGomier https://github.com/luca992/multiplatform-swiftpackage
66. @marcoGomier https://github.com/prof18/kmp-framework-bundler
67. @marcoGomier Where to start
68. @marcoGomier shared androidApp iosApp Gradle Module Framework Same Repository New projects
69. @marcoGomier 🧑🎨 You have a blank canvas
70. @marcoGomier Existing projects Common Kotlin Android App iOS App .aar XCFramework Android App Repository KMP Repository iOs App Repository
71. @marcoGomier 💡 Create a library!
72. @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?
73. @marcoGomier • DTOs • Common Models • Utility methods • Analytics • . . . Where to start?
74. @marcoGomier Start little
75. @marcoGomier Start little Go bigger then
76. @marcoGomier Start little then go bigger • Validate the process with “little” effort • Then you can go bigger and share more “features”
77. @marcoGomier Ecosystem
78. @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 ...
79. @marcoGomier https://github.com/AAkira/Kotlin-Multiplatform-Libraries https://github.com/terrakok/kmp-awesome
80. @marcoGomier https://github.com/touchlab/xcode-kotlin
81. @marcoGomier https://github.com/touchlab/xcode-kotlin
82. @marcoGomier https://github.com/touchlab/xcode-kotlin
83. @marcoGomier https://github.com/touchlab/CrashKiOS
84. @marcoGomier https://github.com/touchlab/CrashKiOS
85. @marcoGomier Conclusions
86. @marcoGomier • Kotlin Multiplatform ! = Cross Platform • Stable since Kotlin 1.9.20 • It’s a joint and team approach Conclusions
87. 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/
88. @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