Building a Multiplatform library for iOS and Android

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Building a Multiplatform Library for Android and iOS David González @dggonzalez malmstein@gmail.com

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expect / actual mechanism

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expect / actual mechanism internal expect fun writeLogMessage(message: String, logLevel: LogLevel)

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expect / actual mechanism fun logDebug(message: String) = writeLogMessage(message, LogLevel.DEBUG) fun logWarn(message: String) = writeLogMessage(message, LogLevel.WARN) fun logError(message: String) = writeLogMessage(message, LogLevel.ERROR)

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expect / actual mechanism internal actual fun writeLogMessage(message: String, logLevel: LogLevel) { println("[$logLevel]: $message") }

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expect / actual mechanism internal actual fun writeLogMessage(message: String, logLevel: LogLevel) { when (logLevel) { LogLevel.DEBUG -> console.log(message) LogLevel.WARN -> console.warn(message) LogLevel.ERROR -> console.error(message) } }

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Native vs Multiplatform

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Native vs Multiplatform apply plugin: ‘kotlin-native-platform' apply plugin: 'kotlin-multiplatform'

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// for Native only projects apply plugin: 'kotlin-native-platform' // for projects targetting multiple platforms apply plugin: 'kotlin-multiplatform' Native vs Multiplatform

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Platform-Speciﬁc declarations

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Platform-Speciﬁc declarations expect class AtomicRef(value: V) { fun get(): V fun set(value: V) fun getAndSet(value: V): V fun compareAndSet(expect: V, update: V): Boolean } actual typealias AtomicRef = java.util.concurrent.atomic.AtomicReference

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Root Folder

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Root Folder AndroidApp SharedCode iOSApp

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Root Folder AndroidApp SharedCode iOSApp build.gradle build src …

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Root Folder AndroidApp SharedCode iOSApp iosApp iosApp.xcodeproj iosAppTests

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Root Folder AndroidApp SharedCode iOSApp Src androidMain androidTest commonMain commonTest iosMain iosTest

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SharedCode Src androidMain androidTest commonMain commonTest iosMain iosTest

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kotlin { sourceSets { commonMain.dependencies { api "org.jetbrains.kotlin:kotlin-stdlib-common:$kotlin_version" implementation “org….:kotlinx-coroutines-core-common:$coroutines_version” implementation "io.ktor:ktor-client:$ktor_version" implementation "io.ktor:ktor-client-core:$ktor_version" implementation "io.ktor:ktor-client-json:$ktor_version" } commonTest.dependencies { implementation "org.jetbrains.kotlin:kotlin-test-common:$version" implementation "org.jetbrains.kotlin:kotlin-test-annotations:$version" } androidMain.dependencies { api "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version" implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core:$version" SharedPhotos/build.gradle

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sourceSets { commonMain.dependencies { api "org.jetbrains.kotlin:kotlin-stdlib-common:$kotlin_version" implementation “org….:kotlinx-coroutines-core-common:$coroutines_version” implementation "io.ktor:ktor-client:$ktor_version" implementation "io.ktor:ktor-client-core:$ktor_version" implementation "io.ktor:ktor-client-json:$ktor_version" } commonTest.dependencies { implementation "org.jetbrains.kotlin:kotlin-test-common:$version" implementation "org.jetbrains.kotlin:kotlin-test-annotations:$version" } androidMain.dependencies { api "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version" implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core:$version" implementation "org.jetbrains.kotlinx:kotlinx-coroutines-android:$version" implementation "io.ktor:ktor-client-android:$ktor_version" implementation "io.ktor:ktor-client-core-jvm:$ktor_version" implementation "io.ktor:ktor-client-json-jvm:$ktor_version" }

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commonTest.dependencies { implementation "org.jetbrains.kotlin:kotlin-test-common:$version" implementation "org.jetbrains.kotlin:kotlin-test-annotations:$version" } androidMain.dependencies { api "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version" implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core:$version" implementation "org.jetbrains.kotlinx:kotlinx-coroutines-android:$version" implementation "io.ktor:ktor-client-android:$ktor_version" implementation "io.ktor:ktor-client-core-jvm:$ktor_version" implementation "io.ktor:ktor-client-json-jvm:$ktor_version" } androidTest.dependencies { implementation "org.jetbrains.kotlin:kotlin-test:$kotlin_version" implementation "org.jetbrains.kotlin:kotlin-test-junit:$kotlin_version" } iosMain.dependencies { implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core-native:$version" implementation "io.ktor:ktor-client-ios:$ktor_version"

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androidMain.dependencies { api "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version" implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core:$version" implementation "org.jetbrains.kotlinx:kotlinx-coroutines-android:$version" implementation "io.ktor:ktor-client-android:$ktor_version" implementation "io.ktor:ktor-client-core-jvm:$ktor_version" implementation "io.ktor:ktor-client-json-jvm:$ktor_version" } androidTest.dependencies { implementation "org.jetbrains.kotlin:kotlin-test:$kotlin_version" implementation "org.jetbrains.kotlin:kotlin-test-junit:$kotlin_version" } iosMain.dependencies { implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core-native:$version" implementation "io.ktor:ktor-client-ios:$ktor_version" implementation "io.ktor:ktor-client-core-native:$ktor_version" implementation "io.ktor:ktor-client-json-native:$ktor_version" } } }

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implementation "io.ktor:ktor-client-core-jvm:$ktor_version" implementation "io.ktor:ktor-client-json-jvm:$ktor_version" } androidTest.dependencies { implementation "org.jetbrains.kotlin:kotlin-test:$kotlin_version" implementation "org.jetbrains.kotlin:kotlin-test-junit:$kotlin_version" } iosMain.dependencies { implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core-native:$version" implementation "io.ktor:ktor-client-ios:$ktor_version" implementation "io.ktor:ktor-client-core-native:$ktor_version" implementation "io.ktor:ktor-client-json-native:$ktor_version" } } }

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apply plugin: 'com.android.application' apply plugin: 'kotlin-android' apply plugin: 'kotlin-android-extensions' dependencies { implementation project(':CloudPhotos') implementation "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version" ... } androidApp/build.gradle

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targets { fromPreset(presets.jvm, 'android') def buildForDevice = project.findProperty("device")?.toBoolean() ?: false def iOSTarget = System.getenv('SDK_NAME')?.startsWith('iphoneos') ? presets.iosArm64 : presets.iosX64 fromPreset(iOSTarget, 'ios') { compilations.main.outputKinds('FRAMEWORK') } } CloudPhotos/build.gradle

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task packForXCode(type: Sync) { final File frameworkDir = new File(buildDir, "xcode-frameworks") final String mode = project.findProperty("XCODE_CONFIGURATION")?.toUpperCase() ?: 'DEBUG' final def framework = kotlin.targets.iOS.binaries.getFramework(“CloudPhotos", mode) inputs.property "mode", mode dependsOn framework.linkTask from { framework.outputFile.parentFile } into frameworkDir doLast { new File(frameworkDir, 'gradlew').with { text = "#!/bin/bash\nexport 'JAVA_HOME=${System.getProperty("java.home")}'\ncd ‘$. {rootProject.rootDir}'\n./gradlew \$@\n" setExecutable(true) } } } tasks.build.dependsOn packForXCode CloudPhotos/build.gradle

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https://github.com/AlecStrong/kotlin-native-cocoapods

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androidMain commonMain iOSMain Multiplatform Library

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androidMain commonMain iOSMain Platform.kt expect fun platformName(): String Multiplatform Library

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androidMain commonMain iOSMain actual fun platformName(): String = "Android Shared Photos" Platform.kt Platform.kt expect fun platformName(): String Multiplatform Library

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androidMain commonMain iOSMain Platform.kt expect fun platformName(): String actual fun platformName(): String = "Android Shared Photos" Platform.kt Platform.kt actual fun platformName(): String = "iOS Shared Photos” Multiplatform Library

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// androidApp/...MainActivity.kt import com.malmstein.sharedphotos.platform.platformName title = platformName() // iosApp/… ViewController.swift import shared self.label.text = PlatformKt.platformName()

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https://github.com/Kotlin/kotlinx.serialization

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internal expect val ApplicationDispatcher: CoroutineDispatcher CloudPhotos/commonMain

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internal actual val ApplicationDispatcher: CoroutineDispatcher = Dispatchers.Main CloudPhotos/androidMain

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internal actual val ApplicationDispatcher: CoroutineDispatcher = NsQueueDispatcher() internal class NsQueueDispatcher: CoroutineDispatcher() { override fun dispatch(context: CoroutineContext, block: Runnable) { val queue = dispatch_get_main_queue() dispatch_async(queue) { block.run() } } } CloudPhotos/iosMain

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class CloudPhotosRepository(private val api: Api = Api()) { private val client: HttpClient = HttpClient { install(JsonFeature) { serializer = KotlinxSerializer(Json.nonstrict).apply { setMapper(InstagramResponseJson::class, InstagramResponseJson.serializer()) } } } suspend fun callInstagram(token: String): InstagramResponseJson = client.get { url("https://api.instagram.com/v1/users/self/media/recent? access_token=$token") } fun loadInstagramAsync(callback: (List) -> Unit) { CloudPhotosRepository

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private val client: HttpClient = HttpClient { install(JsonFeature) { serializer = KotlinxSerializer(Json.nonstrict).apply { setMapper(InstagramResponseJson::class, InstagramResponseJson.serializer()) } } } suspend fun callInstagram(token: String): InstagramResponseJson = client.get { url("https://api.instagram.com/v1/users/self/media/recent? access_token=$token") } fun loadInstagramAsync(callback: (List) -> Unit) { GlobalScope.apply { launch(ApplicationDispatcher) { val photos = api.instagramPhotos(apiToken) .data.map { InstagramPhoto.fromJson(it) } callback(photos) } }

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} } suspend fun callInstagram(token: String): InstagramResponseJson = client.get { url("https://api.instagram.com/v1/users/self/media/recent? access_token=$token") } fun loadInstagramAsync(callback: (List) -> Unit) { GlobalScope.apply { launch(ApplicationDispatcher) { val photos = api.instagramPhotos(apiToken) .data.map { InstagramPhoto.fromJson(it) } callback(photos) } }

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import com.malmstein.sharedphotos.data.CloudPhotosRepository val repository = CloudPhotosRepository() repository.loadInstagramAsync { photosAdapter.setResults(it) } AndroidApp/PhotosActivity.kt

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import shared let api = Api() let repository = CloudPhotosRepository(api: api) typealias PhotoClosure = ([InstagramPhoto]) -> Void func requestPhotos(_ closure: @escaping PhotoClosure) { repository.loadInstagramAsync { photos -> KotlinUnit in closure(gifs) return KotlinUnit() } } requestPhotos { [weak self] photos in iOSApp/ViewController.swift

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let api = Api() let repository = CloudPhotosRepository(api: api) typealias PhotoClosure = ([InstagramPhoto]) -> Void func requestPhotos(_ closure: @escaping PhotoClosure) { repository.loadInstagramAsync { photos -> KotlinUnit in closure(gifs) return KotlinUnit() } } requestPhotos { [weak self] photos in guard let self = self else { return } self.photos = photos self.collectionView?.reloadData() }

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https://github.com/square/sqldelight

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import com.squareup.sqldelight.db.SqlDriver expect object SharedDb { val transacter: CloudPhotosTransacter fun setupDatabase(driver: SqlDriver) fun clearDatabase() } // Called from Swift @Suppress("unused") import com.squareup.sqldelight.drivers.ios.NativeSqliteDriver SharedDb.setupDatabase(NativeSqliteDriver(DatabaseSchema, "SharedPhotosDB"))

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val transacter: CloudPhotosTransacter fun setupDatabase(driver: SqlDriver) fun clearDatabase() } // Called from Swift @Suppress("unused") import com.squareup.sqldelight.drivers.ios.NativeSqliteDriver SharedDb.setupDatabase(NativeSqliteDriver(DatabaseSchema, "SharedPhotosDB")) // Called from Android import com.squareup.sqldelight.android.AndroidSqliteDriver val androidDriver: SqlDriver = AndroidSqliteDriver(DatabaseSchema, context,"SharedPhotosDB") SharedDb.setupDatabase(androidDriver)

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// Called from Swift @Suppress("unused") import com.squareup.sqldelight.drivers.ios.NativeSqliteDriver SharedDb.setupDatabase(NativeSqliteDriver(DatabaseSchema, "SharedPhotosDB")) // Called from Android import com.squareup.sqldelight.android.AndroidSqliteDriver val androidDriver: SqlDriver = AndroidSqliteDriver(DatabaseSchema, context,"SharedPhotosDB") SharedDb.setupDatabase(androidDriver)

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object TokenRepository { fun getToken(): Token { val tokenQueries = SharedDb.transactor.tokenQueries val token = tokenQueries.selectInstagramToken().executeAsOne() return token } commonMain/data/TokenRepository

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package org.jetbrains.kotlinconf.presentation import kotlinx.coroutines.* import kotlin.coroutines.* // TODO: Use Dispatchers.Main instead when it will be supported on iOS open class CoroutinePresenter( private val mainContext: CoroutineContext, private val baseView: BaseView ): CoroutineScope { private val job = Job() private val exceptionHandler = CoroutineExceptionHandler { _, throwable - baseView.showError(throwable) } commonMain/presentation/CoroutinesPresenter

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class InstagramPhotosPresenter(val view: InstagramPhotosView) : CoroutinePresenter() { fun loadInstagramPhotos(): List { view.showLoading() ... val photos = repository.loadInstagramPhotos() view.showPhotos(photos) } commonMain/presentation/InstagramPresenter

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AndroidApp Multiplatform Library iOSApp

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AndroidApp Multiplatform Library iOSApp InstagramPhotosView

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AndroidApp Multiplatform Library iOSApp InstagramPhotosView InstagramActivity: InstagramPhotosView

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AndroidApp Multiplatform Library iOSApp InstagramPhotosView InstagramActivity: InstagramPhotosView InstagramViewController: InstagramPhotosView

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interface InstagramPhotosView { fun showLoading() fun showPhotos(photos: List) fun showError(message: String) } // Calling from Android class InstagramActivity: FragmentActivity(), InstagramPhotosView override fun showLoading() { loadingSpinner.setVisibility(View.VISIBLE) } commonMain/presentation/InstagramPhotosView.kt

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fun showPhotos(photos: List) fun showError(message: String) } // Calling from Android class InstagramActivity: FragmentActivity(), InstagramPhotosView override fun showLoading() { loadingSpinner.setVisibility(View.VISIBLE) } // Calling from iOS class InstagramViewController: UIViewController { extension PhotosViewController: InstagramPhotosView { func showLoading() { self.loadingSpinner.startAnimating() } }

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// Calling from Android class InstagramActivity: FragmentActivity(), InstagramPhotosView override fun showLoading() { loadingSpinner.setVisibility(View.VISIBLE) } // Calling from iOS class InstagramViewController: UIViewController { extension PhotosViewController: InstagramPhotosView { func showLoading() { self.loadingSpinner.startAnimating() } }

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class DateTest { @Test fun testParse() { val date = "2017-10-24T13:31:19".parseDate() assertEquals(2017, date.year) assertEquals(Month.OCTOBER, date.month) assertEquals(24, date.dayOfMonth) assertEquals(13, date.hours) assertEquals(31, date.minutes) } }

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commonTest works if there are no Coroutines involved

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runBlocking does not exist in all platforms

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// commonTest expect fun platformRunBlocking( block: suspend CoroutineScope.() -> T) : T // androidTest + iosTest actual fun platformRunBlocking( block: suspend CoroutineScope.() -> T): T { return runBlocking { block() } } https://github.com/bakkenbaeck/PorchPirateProtector

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@Test fun shouldShowLoadingIndicator() = platformRunBlocking { val view = TestInstagramPhotosView() val presenter = PhotosPresenter(view) val photos = presenter.loadInstagramPhotos() assertTrue(view.loadingIndicatorStarted) ...

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Testing androidMain also tests commonMain

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What is missing Concurrency Date / Time Locale File I / O Networking

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Conclusions Use immutable objects instead of mutable (although…) Keep everyone engaged, not just the Android team Types in Swift / Obj-C can be different in Kotlin and vice-versa Experience developing on iOS is not as good as on Android Can’t debug Kotlin from Xcode (or maybe…)

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https://github.com/touchlab/xcode-kotlin https://github.com/touchlab/KotlinXcodeSync

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https://github.com/touchlab/CrashKiOS

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References Kotlin Conf App: https://github.com/JetBrains/kotlinconf-app SharedPhotosLibrary: https://github.com/malmstein/cloudphotos-mpp Droidcon App Multiplatform: https://github.com/touchlab/DroidconKotlin Repositories: Talks: Kotlin Multiplatform Libraries by Kevin Galligan: Vimeo

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Thank you! David González @dggonzalez malmstein@gmail.com