Meet Kotlin Multiplatform Mobile KMM for short Piotr Prus Mobile Tech Lead @Airly GDG 3City Organizer

Questions I will try to answer - What is the difference between KMM and other multiplatform solutions like a fl utter, react native, etc? - Is this a good solution for your business and why we thought it is a good decision for us? - How does iOS read the shared module? - How much code can we actually share? - What are the most important libraries and what these are doing? - Is KMM production ready? - Pros and cons of KMM

Cross-platform mobile framework popularity Source: www.statista.com, July 2021

Cross-platform mobile framework popularity Source: www.statista.com, July 2021

Google trends

Share code jvm Android iOS Linux macOS Windows JS watchOS tvOS

KMM vs KMP First Multiplatform Kotlin 1.2 November 2017 Announced August 2020

Why we choose KMM • Small team • Business logic in one place • Promote DDD • iOS needed refactor

KMM, the PoC • Con fi guration is tricky, but manageable • Things that works on android, do not need to work on iOS • One repo vs 3 repos • iOS simulator != iOS real device • Sample project != big project 1 week 🎉

Networking October 2021

Networking January 2022 Persistance Models

Networking March 2022 Persistance Models Repositories UseCases

Networking June/July 2022 Persistance Models Repositories UseCases ViewModels

Networking June/July 2022 Persistance Models Repositories UseCases ViewModels UI layer

Share code Domain Repositories Persistance Networking ViewModels Presentation Business(Kotlin) Framework(iOS, Android)

KMM libraries 137 libraries KTOR KOIN SQLdelight Multiplatform settings kotlinx.serialization kotlinx.datetime BuildKon fi g Moko-resources

Networking with KTOR • open-source • lightweight • powered by coroutines • Build by JetBrains

Networking with KTOR fun createHttpClient(httpClientEngine: HttpClientEngine, logger: Logger) = HttpClient(httpClientEngine) { defaultRequest { url.protocol = URLProtocol.HTTP S url.host = BuildKonfig.BASE_UR L parameter("apikey", BuildKonfig.API_KEY ) parameter("Accept-Language", languageCode ?: "en" ) } install(ContentNegotiation) { json(json) } install(Logging) { this.logger = logge r level = logLeve l } }

Networking with KTOR fun createHttpClient(httpClientEngine: HttpClientEngine, logger: Logger) = HttpClient(httpClientEngine) { defaultRequest { url.protocol = URLProtocol.HTTP S url.host = BuildKonfig.BASE_UR L parameter("apikey", BuildKonfig.API_KEY ) parameter("Accept-Language", languageCode ?: "en" ) } install(ContentNegotiation) { json(json) } install(Logging) { this.logger = logge r level = logLeve l } } OkHttp + Retro fi t Retro fi t.Builder().baseUrl() In interceptor: chain.request().header()

Networking with KTOR fun createHttpClient(httpClientEngine: HttpClientEngine, logger: Logger) = HttpClient(httpClientEngine) { defaultRequest { url.protocol = URLProtocol.HTTP S url.host = BuildKonfig.BASE_UR L parameter("apikey", BuildKonfig.API_KEY ) parameter("Accept-Language", languageCode ?: "en" ) } install(ContentNegotiation) { json(json) } install(Logging) { this.logger = logge r level = logLeve l } } OkHttp + Retro fi t Retro fi t.Builder().baseUrl() In interceptor: chain.request().header() .addConverterFactory(jsonConverter)

Networking with KTOR fun createHttpClient(httpClientEngine: HttpClientEngine, logger: Logger) = HttpClient(httpClientEngine) { defaultRequest { url.protocol = URLProtocol.HTTP S url.host = BuildKonfig.BASE_UR L parameter("apikey", BuildKonfig.API_KEY ) parameter("Accept-Language", languageCode ?: "en" ) } install(ContentNegotiation) { json(json) } install(Logging) { this.logger = logge r level = logLeve l } } OkHttp + Retro fi t Retro fi t.Builder().baseUrl() In interceptor: chain.request().header() .addConverterFactory(jsonConverter) .addInterceptor(httpLoggingInterceptor)

Http Client Engine Networking with KTOR Android.create() val logger = object : Logger { override fun log(message: String) { Log.i(tag, message) } } Darwin.create() Logger.DEFAULT Logger

Actual/Expected

Actual/Expected //commo n expect val httpEngine: HttpClientEngin e expect val logger: Logger //androidMai n actual val httpEngine = Android.create( ) actual val logger = object : Logger { override fun log(message: String) { Log.i(tag, message ) } } //iosMai n actual val httpEngine = Darwin.create( ) actual val logger = Logger.DEFAULT

iOS and coroutines

iOS and coroutines Async/Await RxSwift Combine Callbacks

iOS Source: https://dev.to/touchlab/kotlin-coroutines-and-swift-revisited-j5h func createPublisher(flowAdapter: FlowAdapter) -> AnyPublisher { return Deferred>> { let subject = PassthroughSubject( ) let job = flowAdapter.subscribe ( onEvent: { (item) in let _ = subject.send(item) } , onError: { (error) in subject.send(completion: .failure(KotlinError(error))) } , onComplete: { subject.send(completion: .finished) } ) return subject.handleEvents(receiveCancel: { job.cancel(cause: nil ) } ) }.eraseToAnyPublisher( ) }

Shared iOS class FlowAdapter ( private val scope: CoroutineScope , private val flow: Flow ) { fun subscribe ( onEvent: (T) -> Unit , onError: (Throwable) -> Unit , onComplete: () -> Uni t ): Job = flo w .onEach { onEvent(it) } .catch { onError(it) } .onCompletion { onComplete() } .launchIn(scope ) }

SSOT for resources

Resources Moko-resources https://github.com/icerockdev/moko-resources

Strings.xml Resources Cancel Current location Yesterday

Compose Resources stringResource(id = SharedRes.strings.my_string.resourceId) Swift/SwiftUI let string = MR.strings().my_string.desc().localized( ) LocalizedStringKey(MR.strings().email.resourceId)

Resources Common val stringDesc = StringDesc.Resource(SharedRes.strings.airlypedia_title)

Resources Common val stringDesc = StringDesc.Resource(SharedRes.strings.airlypedia_title) .toString(context)

Resources Common val stringDesc = StringDesc.Resource(SharedRes.strings.airlypedia_title) .toString(context) .localized()

Resources Common val stringDesc = StringDesc.Resource(SharedRes.strings.airlypedia_title ) expect fun ResourceStringDesc.getText(): String

Resources Common val stringDesc = StringDesc.Resource(SharedRes.strings.airlypedia_title ) expect fun ResourceStringDesc.getText(): String actual fun ResourceStringDesc.getText(): String = this.toString(appContext )

Resources Common val stringDesc = StringDesc.Resource(SharedRes.strings.airlypedia_title ) expect fun ResourceStringDesc.getText(): String actual fun ResourceStringDesc.getText(): String = this.toString(appContext ) actual fun ResourceStringDesc.getText(): String = this.localized()

How to read KMM in platforms?

No content

dependencies { implementation(project(":shared") ) }

dependencies { implementation(project(":shared") ) }

dependencies { implementation(project(":shared") ) } New Run Script Phase

dependencies { implementation(project(":shared") ) } New Run Script Phase https://kotlinlang.org/docs

Next steps • Use async/await in iOS for suspend functions • Try crashlytics, analytics, etc • Use KMM for web app • Share more assets

iOS & Android everyday

iOS & Android using KMM

Is it ready for production?

KMM - Pros and Cons • 100% Native • Android developers know 
 Kotlin and Gradle • Optional • Still in Alpha

KMM - Pros and Cons • 100% Native • Android developers know 
 Kotlin and Gradle • Optional • Still in Alpha • UI written separately

Meet Kotlin Multiplatform Mobile Thanks for listening! Piotr Prus Mobile Tech Lead @Airly GDG 3City Organizer

Meet Kotlin Multiplatform Mobile Questions? Piotr Prus Mobile Tech Lead @Airly GDG 3City Organizer