Meet Kotlin Multiplatform Mobile KMM for short Loveleen Kaur Senior Engineer (Astrotalk) Google Android Educator

Who am I? ● Loveleen Kaur ● Senior Engineer - Android @ Astrotalk ● Core Team Member @ Google Developer Groups Chandigarh ● Co-Organizer @ Kotlin Chandigarh User Group ● Android Educator @ Android Educators Community India ● Phd Research Scholar ● Technical Speaker ● Develop Mobile Applications ● Happy Android Developer :)

Questions I will try to answer -What is the difference between KMM and other multiplatform solutions like a flutter, 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

Cross-platform mobile framework popularity

Google trends

Share code jvm Android iOS Linux macOS Windows JS watchOS tvOS

KMM First Multiplatform Kotlin 1.2 November 2017 Announced August 2020

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

KMM, the PoC • Configuration 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

Networking October 2021

January 2022 Networking Persistance Models

March 2022 Networking Persistance Models Repositories UseCases

June/July 2022 Networking Persistance Models Repositories UseCases View Models 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 BuildKonfig 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.HTTPS url.host = BuildKonfig.BASE_URL parameter("apikey", BuildKonfig.API_KEY) parameter("Accept-Language", languageCode ?: "en") } install(ContentNegotiation) { json(json) } install(Logging) { this.logger = logger level = logLevel } }

Networking with KTOR fun createHttpClient(httpClientEngine: HttpClientEngine, logger: Logger) = HttpClient(httpClientEngine) { defaultRequest { url.protocol = URLProtocol.HTTPS url.host = BuildKonfig.BASE_URL parameter("apikey", BuildKonfig.API_KEY) parameter("Accept-Language", languageCode ?: "en") } install(ContentNegotiation) { json(json) } install(Logging) { this.logger = logger level = logLevel } } OkHttp + Retrofit Retrofit.Builder().baseUrl() In interceptor: chain.request().header()

fun createHttpClient(httpClientEngine: HttpClientEngine, logger: Logger) = HttpClient(httpClientEngine) { defaultRequest { url.protocol = URLProtocol.HTTPS url.host = BuildKonfig.BASE_URL parameter("apikey", BuildKonfig.API_KEY) parameter("Accept-Language", languageCode ?: "en") } install(ContentNegotiation) { json(json) } install(Logging) { this.logger = logger level = logLevel } } OkHttp + Retrofit Retrofit.Builder().baseUrl( ) In interceptor: chain.request().header( ) .addConverterFactory(jsonConverter) Networking with KTOR

fun createHttpClient(httpClientEngine: HttpClientEngine, logger: Logger) = HttpClient(httpClientEngine) { defaultRequest { url.protocol = URLProtocol.HTTPS url.host = BuildKonfig.BASE_URL parameter("apikey", BuildKonfig.API_KEY) parameter("Accept-Language", languageCode ?: "en") } install(ContentNegotiation) { json(json) } install(Logging) { this.logger = logger level = logLevel } } OkHttp + Retrofit Retrofit.Builder().baseUrl( ) In interceptor: chain.request().header( ) .addConverterFactory(jsonConverter) .addInterceptor(httpLoggingInterceptor) Networking with KTOR

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

Actual/Expected

Actual/Expected //common expect val httpEngine: HttpClientEngine expect val logger: Logger //androidMain actual val httpEngine = Android.create() actual val logger = object : Logger { override fun log(message: String) { Log.i(tag, message) } } //iosMain 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: () -> Unit ): Job = flow .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! Loveleen Kaur Senior Engineer (Astrotalk) Google Android Educator