Kotlin Multiplatform for Android/iOS devs

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Kotlin Multiplatform for Android/iOS devs Paolo Rotolo Mobile developer @ Nextome Anna Labellarte Mobile developer @ Nextome

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What is Kotlin Multiplaform

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What is Kotlin Multiplatform

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What is Kotlin Multiplatform

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What is Kotlin Multiplatform Kotlin/Native • No Vi rt ual Machine • Targets • iOS • Windows, Linux, Mac • Small devices • Interop with C and obj-C Kotlin/JVM • 100 % interop with Java

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Kotlin Multiplatform Mobile Image taken from: https://dev.to/anioutkajarkova/kotlin-multiplatform-practical-multithreading-part-1-4357 Kotlin/Native Kotlin/JVM BETA

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Kotlin Multiplatform Mobile (KMM) BETA

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Kotlin Multiplatform Mobile (KMM) BETA

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KMM Roadmap 2017 Kotlin multiplatform Coroutines First class language for Android Support for iOS Alpha Beta 2018 2019 2020 2022 2022

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Why we decided to give it a shot

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Why we decided to give it a shot - team

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Why we decided to give it a shot - SDK product workflow

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Roadmap 1. Validate the idea with a small library

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Roadmap 2. Transform the existing android project Room Retro fi t Resources DI DateTime

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Roadmap 3. Make it work for iOS

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Roadmap 4. Go on with multipla tf orm 5. Share as much code as we can

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Pros & Cons ✅ Easy to use ✅ Low risks ✅ Easy integration with native code ✅ Shared codebase ✅ Active Community

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Pros & Cons ❌ Code generated not Swi ft -friendly ❌ Build time can be slow on Xcode ❌ Few multipla tf orm libraries

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Inside a KMM app

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Tools Android Studio Kotlin Multipla tf orm Plugin Xcode / AppCode Kotlin Native Plugin

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How to start

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Root project

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plugins { kotlin("multiplatform") kotlin("native.cocoapods") id("com.android.library") } kotlin { android() ios() }

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kotlin { android() ios() sourceSets { val commonMain by getting { dependencies { implementation( "io.ktor:ktor-client-core:$ktor_version") } } val androidMain by getting { dependencies { implementation( "androidx.work:work-runtime-ktx:$work_version") } } val iosMain by getting } }

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val commonMain by getting { dependencies { implementation( "io.ktor:ktor-client-core:$ktor_version") } } val androidMain by getting { dependencies { implementation( "androidx.work:work-runtime-ktx:$work_version") } } val iosMain by getting } } val commonTest by getting val androidTest by getting val iosTest by getting

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plugins { kotlin("multiplatform") kotlin("native.cocoapods") id("com.android.library") } kotlin { android() ios() cocoapods { pod("SSZipArchive") } sourceSets { val commonMain by getting { dependencies { implementation( "io.ktor:ktor-client-core:$ktor_version" } }

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How to write multiplatform code

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How to write multiplatform code

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package com.nextome.hellokmm class Greeting { private val platform: Platform = getPlatform() fun greet(): String { return "Hello, ${platform.name}!" } }

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package com.nextome.hellokmm interface Platform { val name: String } expect fun getPlatform(): Platform

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package com.nextome.hellokmm import android.os.Build.VERSION class AndroidPlatform : Platform { override val name: String = "Android ${VERSION.SDK_INT}" } actual fun getPlatform(): Platform = AndroidPlatform()

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package com.nextome.hellokmm import platform.UIKit.UIDevice class IOSPlatform: Platform { override val name: String = UIDevice.currentDevice.systemName() + " " + UIDevice.currentDevice.systemVersion } actual fun getPlatform(): Platform = IOSPlatform()

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Publish multiplatform libraries

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/ / build.gradle.kts (:shared) plugins { kotlin("multiplatform") id(“com.android.library”) }

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/ / build.gradle.kts (:shared) plugins { kotlin("multiplatform") id(“com.android.library”) id("maven-publish") } group = "com.nextome.hellokmm" version = "1.0.0"

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// build.gradle.kts (:shared) plugins { kotlin("multiplatform") id(“com.android.library”) id("maven-publish") } group = "com.nextome.hellokmm" version = “1.0.0" kotlin { android{ publishLibraryVariants("release", "debug") } // [ ... ] }

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./gradlew publishToMavenLocal // build.gradle.kts (:shared) plugins { kotlin("multiplatform") id(“com.android.library”) id("maven-publish") } group = "com.nextome.hellokmm" version = “1.0.0" kotlin { android{ publishLibraryVariants("release", "debug") }

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sourceSets { val commonMain by getting { dependencies { implementation("com.nextome.hellokmm:hellokmm:1.0.0") } } } Consume libraries

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Useful libraries for KMM

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Retrofit, OkHttp ➡ Ktor

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Ktor suspend fun main() { val client = HttpClient() val response: HttpResponse = client.get("https: / / ktor.io/") println(response.status) client.close() }

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Ktor suspend fun main() { val client = HttpClient() { install(ContentNegotiation) { json() } } val response: HttpResponse = client.get("https: / println(response.status) client.close() }

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install(Auth) { bearer { loadTokens { bearerTokenStorage.last() } refreshTokens { val refresh = this.oldTokens.refreshToken getNewToken(refresh) } } } suspend fun main() { val client = HttpClient() { install(ContentNegotiation) { json() } }

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bearerTokenStorage.last() } refreshTokens { val refresh = this.oldTokens.refreshToken getNewToken(refresh) } } } } / install(Logging) { logger = Logger.DEFAULT level = LogLevel.HEADERS filter { request -> request.url.host.contains("ktor.io") } }

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/ filter { request -> request.url.host.contains("ktor.io") } } HttpResponseValidator { handleResponseExceptionWithRequest { exception, request -> val clientException = exception as? ClientRequestException ?: return@handleResponseExceptionWithRequest when (clientException.response.status) { HttpStatusCode.NotFound - > { throw MissingPageException(exceptionResponse) } } } }

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Gson, Moshi ➡ kotlinx-serialization

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kotlinx-serialization @Serializable data class User(val name: String, val email: String) fun main() { val data = User("Paolo", “[email protected]”) val serializedData: String = Json.encodeToString(data) println(serializedData) // {“name”:"Paolo","email":"[email protected]"} val deserializedData: User = Json.decodeFromString(serializedData) println(deserializedData) // Project(name=Paolo, [email protected]) }

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Room Rx*, LiveData Timber Hilt, Koin SqlDelight / Realm Coroutines & Flow Kermit Koin ➡ ➡ ➡ ➡ Retrofit, OkHttp Gson, Moshi ➡ Ktor ➡ kotlinx-serialization

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SharedPreferences, DataStore -> DataStore

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JetPack Multiplatform Libraries Compose DataStore Collections preview preview

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The Dark side of KMM

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Make it debuggable on iOS

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Data Types fun insertNewTodo( title: String, priority: Int )

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Data Types fun insertNewTodo( title: String, priority: Int ) repository.insertNewTodo( title: String, priority: ? Int32 )

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Data Types fun insertNewTodo( title: String, priority: Int ) repository.insertNewTodo( title: String, priority: ? ) KotlinInt?

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Coroutines class TodoRepository { suspend fun fetchTodo(): List { val todos = getTodoFromServer() saveToDb(todos) return todos } }

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Coroutines class TodoRepository { suspend fun fetchTodo(): List { val todos = getTodoFromServer() saveToDb(todos) return todos } } scope.launch { val todo = TodoRepository().fetchTodo() }

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Coroutines class TodoRepository { suspend fun fetchTodo(): List { val todos = getTodoFromServer() saveToDb(todos) return todos } } TodoRepository().fetchTodo {todos, error in } func loadTodo() async throws { let todo = try await TodoRepository().fetchTodo() }

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Coroutines class TodoRepository { suspend fun fetchTodo(): List { val todos = getTodoFromServer() saveToDb(todos) return todos } } scope.launch { val todo = TodoRepository().fetchTodo() }

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Coroutines class TodoRepository { suspend fun fetchTodo(): List { val todos = getTodoFromServer() saveToDb(todos) return todos } } scope.launch { val todo = TodoRepository().fetchTodo() } scope.cancel()

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Koru Inspired by https://touchlab.co/kotlin-coroutines-rxswift/

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Koru Inspired by https://touchlab.co/kotlin-coroutines-rxswift/ plugins { // add ksp and koru compiler plugin id("com.google.devtools.ksp") version "1.6.21-1.0.6" id("com.futuremind.koru").version("0.11.1") } kotlin { sourceSets { val commonMain by getting { dependencies { // add library dependency implementation("com.futuremind:koru:0.11.1") } } val iosMain by creating { ... } } } koru { nativeSourceSetNames = listOf("iosMain") }

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Coroutines class TodoRepository { suspend fun fetchTodo(): List { val todos = getTodoFromServer() saveToDb(todos) return todos } }

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Coroutines @ToNativeClass(name = "TodoRepositoryIos") class TodoRepository { suspend fun fetchTodo(): List { val todos = getTodoFromServer() saveToDb(todos) return todos } }

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// build/generated/ksp/TodoRepositoryIos.kt public class TodoRepositoryIos( private val wrapped: TodoRepository, private val scopeProvider: ScopeProvider?, ) { public constructor(wrapped: TodoRepository) : this(wrapped,exportedScopeProvider_mainScopeProvider) public fun fetchTodo(): SuspendWrapper = SuspendWrapper(scopeProvider, false) { wrapped.fetchTodo() } }

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Coroutines @ToNativeClass(name = "TodoRepositoryIos") class TodoRepository { suspend fun fetchTodo(): List { val todos = getTodoFromServer() saveToDb(todos) return todos } }

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Coroutines @ToNativeClass(name = "TodoRepositoryIos") class TodoRepository { suspend fun fetchTodo(): List { val todos = getTodoFromServer() saveToDb(todos) return todos } } let repo = TodoRepositoryIos( wrapped: TodoRepository(), scope: coroutineScope) repo.getTodoWrapped().subscribe( onSuccess: { (array: NSArray?) -> () in }, onThrow: { throwable in })

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@ToNativeClass(name = "TodoRepositoryIos") class TodoRepository { suspend fun fetchTodo(): List { val todos = getTodoFromServer() saveToDb(todos) return todos } }

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@ToNativeClass(name = "TodoRepositoryIos", launchOnScope = MainScopeProvider :: class) class TodoRepository { suspend fun fetchTodo(): List { val todos = getTodoFromServer() saveToDb(todos) return todos } } @ExportedScopeProvider class MainScopeProvider : ScopeProvider { override val scope : CoroutineScope = MainScope() }

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@ToNativeClass(name = "TodoRepositoryIos", launchOnScope = MainScopeProvider :: class) class TodoRepository { suspend fun fetchTodoList(): TodoList { val todos = getTodoFromServer() saveToDb(todos) return TodoList(todos) } } @ExportedScopeProvider class MainScopeProvider : ScopeProvider { override val scope : CoroutineScope = MainScope() } data class TodoList(val list: List)

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@ToNativeClass(name = "TodoRepositoryIos", launchOnScope = MainScopeProvider :: class) class TodoRepository { suspend fun fetchTodoList(): TodoList { val todos = getTodoFromServer() saveToDb(todos) return TodoList(todos) } } Coroutines let repo = TodoRepositoryIos(wrapped: TodoRepository()) repo.fetchTodoList().subscribe(onSuccess: { (list: TodoList?) in }, onThrow: { (throwable: KotlinThrowable) in })

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@ToNativeClass(name = "TodoRepositoryIos", launchOnScope = MainScopeProvider :: class) class TodoRepository { suspend fun fetchTodoList(): TodoList { val todos = getTodoFromServer() saveToDb(todos) return TodoList(todos) } } Coroutines let repo = TodoRepositoryIos(wrapped: TodoRepository()) let job = repo.fetchTodoList().subscribe(onSuccess: { (list: TodoList?) in }, onThrow: { (throwable: KotlinThrowable) in }) job.cancel(cause: KotlinCancellationException(message: "Stop it!"))

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Flow class RandomIntGenerator { fun generateEach(interval: Long) = flow { while(true) { delay(interval) emit(Random.nextInt()) } } }

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Flow class RandomIntGenerator { fun generateEach(interval: Long) = flow { while(true) { delay(interval) emit(Random.nextInt()) } } } lifecycleScope.launch { RandomIntGenerator().generateEach(ONE_SECOND).collect { print(it) } }

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Flow class RandomIntGenerator { fun generateEach(interval: Long) = flow { while(true) { delay(interval) emit(Random.nextInt()) } } } RandomIntGenerator() .generateEachTest(interval: Int64(1000)) .collect(collector: Collector()) { error in } class Collector: Kotlinx_coroutines_coreFlowCollector{ func emit(value: Any?, completionHandler: @escaping (Error?) -> Void) { print(value) completionHandler(nil) } }

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RandomIntGenerator() .generateEachTest(interval: Int64(1000)) .collect(collector: Collector()) { error in } class Collector: Kotlinx_coroutines_coreFlowCollector{ func emit(value: Any?, completionHandler: @escaping (Error?) -> Void) { print(value) completionHandler(nil) } }

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RandomIntGenerator() .generateEach(interval: ONE_SECOND) .collect(collector: Collector() { value in print(value) }) { (error) in print(error?.localizedDescription) } class Collector: Kotlinx_coroutines_coreFlowCollector { let callback:(T) -> Void init(callback: @escaping (T) -> Void) { self.callback = callback } func emit(value: Any?, completionHandler: @escaping (Error?) -> Void) { callback(value as! T) completionHandler(nil) } }

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class RandomIntGenerator { fun generateEach(interval: Long) = flow { while(true) { delay(interval) emit(Random.nextInt()) } } }

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class RandomIntGenerator { fun generateEach(interval: Long) = flow { while(true) { delay(interval) emit(Random.nextInt()) } } } fun Flow.wrap(): CFlow = CFlow(this) class CFlow(private val origin: Flow) : Flow by origin { fun watch(block: (T) -> Unit): Closeable { val job = Job() onEach { block(it) }.launchIn(CoroutineScope(Dispatchers.Main + job)) return object : Closeable { override fun close() { job.cancel() } } } }

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class RandomIntGenerator { fun generateEach(interval: Long): CFlow = flow { while(true) { delay(interval) emit(Random.nextInt()) } }.wrap() } fun Flow.wrap(): CFlow = CFlow(this) class CFlow(private val origin: Flow) : Flow by origin { fun watch(block: (T) > val job = Job() onEach { block(it) }.launchIn(CoroutineScope(Dispatchers.Main + job)) return object : Closeable { override fun close() { job.cancel() } } } }

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class RandomIntGenerator { fun generateEach(interval: Long): CFlow = flow { while(true) { delay(interval) emit(Random.nextInt()) } }.wrap() } RandomIntGenerator() .generateEach(interval: ONE_SECOND) .watch { (value: KotlinInt?) in print(value) }

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let disposable = RandomIntGenerator() .generateEach(interval: ONE_SECOND) .watch { (value: KotlinInt?) in print(value) } disposable.close() class RandomIntGenerator { fun generateEach(interval: Long): CFlow = flow { while(true) { delay(interval) emit(Random.nextInt()) } }.wrap() }

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Error Handling UNCHECKED EXCEPTIONS CHECKED EXCEPTIONS

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Error Handling

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Error Handling

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Error Handling

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Error Handling

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Error Handling

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Error Handling

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Error Handling

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Default parameters

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Default parameters

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Default parameters

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Default parameters

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Sealed Class

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Sealed Class

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Sealed Class when (uiState) { is UIState.Data -> TODO() is UIState.Error - > TODO() is UIState.Loading - > TODO() }

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Sealed Class

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Sealed Class Enum

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Sealed Class

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In the end… Share common logic in Kotlin Work together to make it work be tt er!

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In the end… Share common logic in Kotlin Work together to make it work be tt er! Sometimes it could be ugly but we’re ge tt ing there (fast)

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Thanks!