Kotlin Multiplatform: Sharing code between Android and iOS Wellington Costa Pereira Mobile Engineer @ Hash 

What is Kotlin Multiplatform? 

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It’s an open source project developed and maintained by Jetbrains and some companies such as Square and Touchlab, that enables optional code sharing for several platforms, natively integrated, and based on Kotlin Programming Language. What is Kotlin Multiplatform? 

It’s an open source project developed and maintained by Jetbrains and some companies such as Square and Touchlab, that enables optional code sharing for several platforms, natively integrated, and based on Kotlin Programming Language. The main advantage is the capability of write Kotlin code, e.g. business code, that can be shared to several platforms, and compile it to native code, saving efforts to write the same code in different languages for each platforms. What is Kotlin Multiplatform? 

Optional You can decide which code to share 

Natively integrated It compiles to native code with low efforts 

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Code sharing Not “cross platform” 

Not UI code Share logic code and infrastructure code 

Supported platforms 

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Under the hood… 

:shared: 

:shared: Kotlin IR 

:shared: Kotlin IR Android iOS Windows Linux JVM Javascript 

expect/actual 

expect/actual mechanism "// In common code expect val isMainThread: Boolean 

expect/actual mechanism "// In common code expect val isMainThread: Boolean "// In Android/JVM actual val isMainThread: Boolean get() = Looper.getMainLooper() ""=== Looper.myLooper() 

expect/actual mechanism "// In common code expect val isMainThread: Boolean "// In Android/JVM actual val isMainThread: Boolean get() = Looper.getMainLooper() ""=== Looper.myLooper() "// In iOS/Native actual val isMainThread: Boolean get() = NSThread.isMainThread() 

Weapons starter pack 

Weapons starter pack • SQLDelight 

SQLDelight SQLDelight generates typesafe APIs from SQL statements and verifies at compile-time the schemas, statements, migrations, and so on. 

SQLDelight SQLDelight generates typesafe APIs from SQL statements and verifies at compile-time the schemas, statements, migrations, and so on. It also provides IDE features like autocomplete. 

SQLDelight SQLDelight generates typesafe APIs from SQL statements and verifies at compile-time the schemas, statements, migrations, and so on. It also provides IDE features like autocomplete. SQLDelight currently supports the SQLite dialect, and there are supported drivers for Android, JVM, iOS and Windows. 

Why SQL code? 

SQLDelight • SQL is standardized. 

SQLDelight • SQL is standardized. • Everyone understands SQL. 

SQLDelight • SQL is standardized. • Everyone understands SQL. • It’s not required to learn a custom DSL of an ORM library. 

SQLDelight • SQL is standardized. • Everyone understands SQL. • It’s not required to learn a custom DSL of an ORM library. • You write SQL code and let SQLDelight generates Kotlin code. 

How? 

SQLDelight • Write SQL into .sq files 

SQLDelight • Write SQL into .sq files • Build the project 

SQLDelight • Write SQL into .sq files • Build the project • Use generated code! 

SQLDelight • Write SQL into .sq files • Build the project • Use generated code! • Migrate you database writing code into .sqm files 

SQLDelight dependencies { classpath("com.squareup.sqldelight:gradle-plugin:1.3.0") } 

SQLDelight dependencies { classpath("com.squareup.sqldelight:gradle-plugin:1.3.0") } plugins { id("com.squareup.sqldelight") } 

SQLDelight dependencies { classpath("com.squareup.sqldelight:gradle-plugin:1.3.0") } plugins { id("com.squareup.sqldelight") } sqldelight { database(name = "TodoAppDatabase") { packageName = "io.github.wellingtoncosta.todoapp" } } 

SQLDelight 
 // For Android target
 implementation("com.squareup.sqldelight:android-driver:1.3.0") 

SQLDelight 
 // For Android target
 implementation("com.squareup.sqldelight:android-driver:1.3.0") // For iOS target implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core-native:1.3.7") 

SQLDelight // Todo.sq file
 CREATE TABLE todos ( id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT, external_id TEXT UNIQUE DEFAULT NULL, title TEXT NOT NULL, description TEXT, status TEXT AS TodoStatus NOT NULL ); 

SQLDelight // Todo.sq file
 selectAll: SELECT * FROM todos; selectByExternalId: SELECT * FROM todos WHERE external_id = ?; insert: INSERT INTO todos (external_id, title, description, status) VALUES (?,?,?,?); updateStatus: UPDATE todos SET status = ? WHERE id = ?; 

Tahdah! 

• SQLDelight • Ktor Weapons starter pack 

Ktor Ktor is an open source project sponsored by Jetbrains for building backend applications. 

Ktor Ktor is an open source project sponsored by Jetbrains for building backend applications. It also has a HTTP client that supports several platforms using Kotlin Multiplatform. 

Ktor Ktor is an open source project sponsored by Jetbrains for building backend applications. It also has a HTTP client that supports several platforms using Kotlin Multiplatform. Currently, the supported platforms are Android, JVM, iOS, JS and native. 

Ktor 
 // For common module
 implementation(“io.ktor:ktor-client-core:1.3.2”) 

Ktor 
 // For common module
 implementation(“io.ktor:ktor-client-core:1.3.2”) // For Android target implementation(“io.ktor:ktor-client-android:1.3.2”) 

Ktor 
 // For common module
 implementation(“io.ktor:ktor-client-core:1.3.2”) // For Android target implementation(“io.ktor:ktor-client-android:1.3.2”) // For iOS target implementation(“io.ktor:ktor-client-ios:1.3.2”) 

Ktor // Common code expect val engine: HttpClientEngineFactory 

Ktor // Common code expect val engine: HttpClientEngineFactory val client = HttpClient(engine) { … } 

Ktor // Common code expect val engine: HttpClientEngineFactory val client = HttpClient(engine) { install(JsonFeature) { serializer = KotlinxSerializer(json) } } 

Ktor // Common code expect val engine: HttpClientEngineFactory val client = HttpClient(engine) { install(JsonFeature) { serializer = KotlinxSerializer(json) } install(Logging) { logger = Logger.SIMPLE level = LogLevel.ALL } … } 

Ktor // Common code suspend fun getAll(): List { return client.get { url { path("todos") } } } 

Ktor // Common code suspend fun getAll(): List { return client.get { url { path("todos") } } } suspend fun save(request: SaveTodoRequest): TodoResponse { return client.post { url { path("todos") } header(HttpHeaders.ContentType, ContentType.Application.Json) body = request } } 

• SQLDelight • Ktor • Kotlin Serialization Weapons starter pack 

Kotlin Serialization dependencies { classpath("org.jetbrains.kotlin:kotlin-serialization:1.3.72") } 

Kotlin Serialization dependencies { classpath("org.jetbrains.kotlin:kotlin-serialization:1.3.72") } // Common code implementation("org.jetbrains.kotlinx:kotlinx-serialization-runtime-common:0.20.0") 

Kotlin Serialization dependencies { classpath("org.jetbrains.kotlin:kotlin-serialization:1.3.72") } // Common code implementation(“org.jetbrains.kotlinx:kotlinx-serialization-runtime-common:0.20.0") // Android target implementation(“org.jetbrains.kotlinx:kotlinx-serialization-runtime:0.20.0") 

Kotlin Serialization dependencies { classpath("org.jetbrains.kotlin:kotlin-serialization:1.3.72") } // Common code implementation(“org.jetbrains.kotlinx:kotlinx-serialization-runtime-common:0.20.0") // Android target implementation(“org.jetbrains.kotlinx:kotlinx-serialization-runtime:0.20.0") // iOS target implementation("org.jetbrains.kotlinx:kotlinx-serialization-runtime-native:0.20.0") 

Kotlin Serialization @Serializable data class TodoResponse( val id: String, val title: String, val description: String? = null, val status: TodoStatus ) 

Kotlin Serialization @Serializable data class TodoResponse( val id: String, val title: String, val description: String? = null, val status: TodoStatus ) @Serializable data class SaveTodoRequest( val title: String, val description: String?, val status: TodoStatus ) 

• SQLDelight • Ktor • Kotlin Serialization • Kotlin Coroutines Weapons starter pack 

• SQLDelight • Ktor • Kotlin Serialization • Kotlin Coroutines • Kotlin/Native Cocoapod plugin Weapons starter pack 

Kotlin/Native Cocoapod plugin plugins { id("org.jetbrains.kotlin.native.cocoapods") } 

Kotlin/Native Cocoapod plugin plugins { id("org.jetbrains.kotlin.native.cocoapods") } cocoapods { authors = "Wellington Costa Pereira" license = "MIT" summary = "Common core for Todo App." homepage = "https://github.com/wellingtoncosta/todo-app-kotlin-multiplatform" } 

Kotlin/Native Cocoapod plugin Pod::Spec.new do |spec| spec.name = 'shared' spec.version = '1.0' spec.homepage = 'https://github.com/wellingtoncosta/todo-app-kotlin-multiplatform' spec.source = { :git => "Not Published", :tag => "Cocoapods/#{spec.name}/#{spec.version}" } spec.authors = 'Wellington Costa Pereira' spec.license = 'MIT' spec.summary = 'Common core for Todo App.' spec.static_framework = true spec.vendored_frameworks = "build/cocoapods/framework/shared.framework" spec.libraries = "c++" spec.module_name = "#{spec.name}_umbrella" spec.pod_target_xcconfig = { 'KOTLIN_TARGET[sdk=iphonesimulator*]' => 'ios_x64', 'KOTLIN_TARGET[sdk=iphoneos*]' => 'ios_arm', 'KOTLIN_TARGET[sdk=watchsimulator*]' => 'watchos_x86', 'KOTLIN_TARGET[sdk=watchos*]' => 'watchos_arm', 'KOTLIN_TARGET[sdk=appletvsimulator*]' => 'tvos_x64', 'KOTLIN_TARGET[sdk=appletvos*]' => 'tvos_arm64', 'KOTLIN_TARGET[sdk=macosx*]' => 'macos_x64' } spec.script_phases = [ { :name => 'Build shared', :execution_position => :before_compile, :shell_path => '/bin/sh', :script => <<-SCRIPT set -ev REPO_ROOT="$PODS_TARGET_SRCROOT" "$REPO_ROOT/../gradlew" -p "$REPO_ROOT" :shared:syncFramework \ -Pkotlin.native.cocoapods.target=$KOTLIN_TARGET \ -Pkotlin.native.cocoapods.configuration=$CONFIGURATION \ -Pkotlin.native.cocoapods.cflags="$OTHER_CFLAGS" \ -Pkotlin.native.cocoapods.paths.headers="$HEADER_SEARCH_PATHS" \ -Pkotlin.native.cocoapods.paths.frameworks="$FRAMEWORK_SEARCH_PATHS" SCRIPT } ] end 

Kotlin/Native Cocoapod plugin target 'TodoApp' do # Comment the next line if you don't want to use dynamic frameworks use_frameworks! # Pods for TodoApp pod 'SnapKit', '~> 5.0.1' pod 'shared', :path => '../shared' target 'TodoAppTests' do inherit! :search_paths # Pods for testing end target 'TodoAppUITests' do # Pods for testing end end 

Kotlin/Native Cocoapod plugin target 'TodoApp' do # Comment the next line if you don't want to use dynamic frameworks use_frameworks! # Pods for TodoApp pod 'SnapKit', '~> 5.0.1' pod 'shared', :path => '../shared' target 'TodoAppTests' do inherit! :search_paths # Pods for testing end target 'TodoAppUITests' do # Pods for testing end end 

What’s next? 

• Incremental builds What’s next? 

• Incremental builds • Write tests What’s next? 

• Incremental builds • Write tests • Modularization What’s next? 

• Incremental builds • Write tests • Modularization • Experiment Bazel Build What’s next? 

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Questions? 

Thank you! ;) wellingtoncosta wellingtoncosta128 [email protected]