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

Marco Gomiero @marcoGomier 👨💻 Senior Android Developer @ Airalo Google
Developer Expert for Kotlin Hi, have you met Kotlin Multiplatform?

@marcoGomier https://www.youtube.com/watch?v=ddcZnW1HKUY

@marcoGomier “Classic” Cross Platform Solutions • All-in approach • Everything
is shared, UI included • Different platforms have different patterns

@marcoGomier Kotlin Multiplatform • Incremental approach • You choose what
to share (even UI, if you want)

@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

@marcoGomier Common Kotlin Kotlin/JVM Kotlin/JS Kotlin/Native JVM Android Browser NodeJS
iOS macOS watchOS tvOS Linux Windows Mobile Kotlin/Wasm Browser Alpha

@marcoGomier Common and Platform-specific code • Write regular Kotlin code
in the common source set • Platform-specific code goes into platform source sets

@marcoGomier Platform-specific code • Expect/Actual

@marcoGomier Expect/Actual https://kotlinlang.org/docs/multiplatform-connect-to-apis.html

@marcoGomier Expect/Actual expect fun debugLog(tag: String, message: String)

@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) } }

@marcoGomier Platform-specific code • Expect/Actual • Interfaces

@marcoGomier internal interface XmlFetcher { suspend fun fetchXml(url: String): ParserInput
} Interface

@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 -> ... } }

@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? }

@marcoGomier Platform-specific code • Expect/Actual • Interfaces • Prefer interfaces,
if possible

@marcoGomier How it works?

@marcoGomier shared androidApp iosApp Library Library iOS Android

@marcoGomier shared androidApp Library Android

@marcoGomier shared androidApp .aar/Gradle module Android Just “regular” Kotlin code,
like yet another library

@marcoGomier shared androidApp iosApp .aar/Gradle Module Library iOS Android

@marcoGomier shared iosApp Library iOS

@marcoGomier shared iosApp Framework iOS

@marcoGomier XCFramework https://developer.apple.com/documentation/xcode/creating-a-multi-platform-binary-framework-bundle

@marcoGomier NEW https://devstreaming-cdn.apple.com/videos/wwdc/2019/416h8485aty341c2/416/416_binary_frameworks_in_swift.pdf

@marcoGomier https://devstreaming-cdn.apple.com/videos/wwdc/2019/416h8485aty341c2/416/416_binary_frameworks_in_swift.pdf NEW iOS mac OS watch OS tvOS

@marcoGomier shared iosApp Framework iOS Kotlin Objective-C Swift -> ->

@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 ... } }

@marcoGomier Some gotchas • No namespaces • No default parameters
• Enums are not Swift-friendly (no values) • Sealed classes are simple classes • Coroutines without cancellation • Flows

@marcoGomier https://github.com/rickclephas/KMP-NativeCoroutines

@marcoGomier https://github.com/touchlab/SKIE

@marcoGomier Make it a team effort

@marcoGomier New projects

@marcoGomier Create a new app project

@marcoGomier

@marcoGomier shared androidApp Gradle Module Android

@marcoGomier // settings.gradle.kts include(":shared") // build.gradle.kts implementation(project(":shared")) Android

@marcoGomier shared androidApp iosApp Gradle Module Framework iOS Android

@marcoGomier Regular Framework

@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

@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

@marcoGomier shared androidApp iosApp Gradle Module Framework iOS Android

@marcoGomier shared androidApp iosApp Framework Same Repository Gradle Module

@marcoGomier https://kmp.jetbrains.com/#newProject

@marcoGomier Existing projects

@marcoGomier 🙅 shared androidApp iosApp Gradle Module Framework Same Repository
Existing projects

@marcoGomier 💡 Create a library!

@marcoGomier Create a new library project

@marcoGomier

@marcoGomier Common Kotlin Android App iOS App .aar XCFramework

@marcoGomier Common Kotlin Android App iOS App .aar XCFramework Android
App Repository KMP Repository iOs App Repository

@marcoGomier https://terrakok.github.io/kmp-web-wizard/

@marcoGomier How to publish: Android

@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") } } }

@marcoGomier Publish the artifacts ./gradlew publish

@marcoGomier Publish the artifacts ./gradlew publish ./gradlew publishToMavenLocal

@marcoGomier How to publish: iOS

@marcoGomier 🥵

@marcoGomier XCFramework

@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 } } }

@marcoGomier XCFramework: Gradle tasks assemble${libName}XCFramework assemble${libName}DebugXCFramework assemble${libName}ReleaseXCFramework

@marcoGomier Build an XCFramework

@marcoGomier https://github.com/touchlab/KMMBridge

@marcoGomier https://github.com/prof18/kmp-framework-bundler

@marcoGomier Where to start

@marcoGomier shared androidApp iosApp Gradle Module Framework Same Repository New
projects

@marcoGomier 🧑🎨 You have a blank canvas

@marcoGomier Existing projects Common Kotlin Android App iOS App .aar
XCFramework Android App Repository KMP Repository iOs App Repository

@marcoGomier 💡 Create a library!

@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?

@marcoGomier • DTOs • Common Models • Utility methods •
Analytics • . . . Where to start?

@marcoGomier Start little

@marcoGomier Start little Go bigger then

@marcoGomier Start little then go bigger • Validate the process
with “little” effort • Then you can go bigger and share more “features”

@marcoGomier Ecosystem

@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

@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 ...

@marcoGomier https://github.com/AAkira/Kotlin-Multiplatform-Libraries https://github.com/terrakok/kmp-awesome

@marcoGomier https://github.com/touchlab/xcode-kotlin

@marcoGomier https://www.jetbrains.com/ fl eet/

@marcoGomier https://github.com/touchlab/CrashKiOS

@marcoGomier Conclusions

@marcoGomier • Kotlin Multiplatform ! = Cross Platform • Stable
since Kotlin 1.9.20 • It’s a joint and team approach Conclusions

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/

@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

Hi, have you met Kotlin Multiplatform? | Kotlin...

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

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