Challenges of Building Kotlin Multiplatform Libraries

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Mohit Sarveiya Building Kotlin Multiplatform Libraries @heyitsmohit

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Building Kotlin Multiplatform Libraries ● Setting up KMM project ● CI Challenges ● API Design Challenges

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Why Kotlin Multiplatform? Android Kotlin/JVM iOS Swift/LLVM Web JS

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Why Kotlin Multiplatform? API API API

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Why Kotlin Multiplatform? Retrofit Ajax Alamofire

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Why Kotlin Multiplatform? Room/SQL Delight Core Data

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Why Kotlin Multiplatform? Business Logic Business Logic Business Logic

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Why Kotlin Multiplatform? MVP/MVVM/MVI ReactJs VIPER

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Why Kotlin Multiplatform? Shared code

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Why Kotlin Multiplatform? API Business Logic Analytics Cache

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Setting up KMM Project

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Use Case Show platform name Hello   Android

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Hello   iOS Use Case 9:41 Show platform name

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Greeter Use Case

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How to create Multiplatform app

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Plugin https: // plugins.jetbrains.com/plugin/14936-kotlin-multiplatform-mobile

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Project Setup Shared

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Project Setup Shared Android App

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Project Setup Shared Android App iOS App XCode Project

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Project Setup Shared Android App iOS App

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Project Setup Shared Android App iOS App Framework

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Project Setup Shared Android App iOS App

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Shared Module Structure

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Shared Module Shared src commonMain

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Shared Module Shared src commonMain androidMain

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Shared Module Shared src commonMain androidMain iOSMain

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Greeter Use Case

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Common Shared Module Android iOS Platform name

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Common expect class Platform() { val platform: String }

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Common expect class Platform() { val platform: String }

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Common expect class Platform() { val platform: String }

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Common expect class Platform() { val platform: String } Common

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Common Android Android iOS Platform name

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Android actual class Platform actual constructor() { actual val platform: String = ”Android” }

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Android actual class Platform actual constructor() { actual val platform: String = ”Android” }

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Android actual class Platform actual constructor() { actual val platform: String = ”Android” }

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Android actual class Platform actual constructor() { actual val platform: String = ”Android” } Common Android

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Common iOS Android iOS Platform name

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iOS actual class Platform actual constructor() { actual val platform: String = “iOS” }

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Common Shared Module Android iOS Platform name

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Common class Greeter { fun greet(): String { return "Hello ${Platform().platform}!" } }

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Common class Greeter { fun greet(): String { return "Hello ${Platform().platform}!" } }

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Using Shared Module

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Project Setup Shared Android App iOS App

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Use Case Show platform name Hello   Android

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Android App class MainActivity : AppCompatActivity() { }

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Android App class MainActivity : AppCompatActivity() { fun onCreate( ... ) { val greeting = Greeter().greet() } }

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Android App class MainActivity : AppCompatActivity() { fun onCreate( ... ) { val greeting = Greeter().greet() textView.text = greeting } }

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Android App class Greeter { ... } Common Source Build

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Use Case Hello   Android

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Android App class MainActivity : AppCompatActivity() { fun onCreate( ... ) { val greeting = Greeter().greet() textView.text = greeting } }

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Hello   iOS Use Case 9:41 Show platform name

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iOS App class Greeter { ... } Common Source Build Framework

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iOS App import SwiftUI import shared

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iOS App import SwiftUI import shared func greet() -> String { return Greeting().greeting() }

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iOS App import SwiftUI import shared struct ContentView: View { var body: some View { } }

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iOS App import SwiftUI import shared struct ContentView: View { var body: some View { Text(greet()) } }

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Hello   iOS Use Case 9:41 Show platform name

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Inside Objective-C Framework

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iOS Framework class Greeter { ... } Common Source Build Framework

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iOS Framework import SwiftUI import shared func greet() -> String { return Greeting().greeting() }

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iOS Framework Shared Base Shared Platform Shared Greeting

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Shared Base __attribute__((swift_name("KotlinBase"))) @interface SharedBase : NSObject ... @end;

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Shared Base __attribute__((swift_name("KotlinBase"))) @interface SharedBase : NSObject ... @end;

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iOS actual class Platform actual constructor() { actual val platform: String = “iOS” }

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Mappings https: // kotlinlang.org/docs/native-objc-interop.html#mappings

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Shared Platform __ attribute __ ((swift_name(“Platform"))) @interface SharedPlatform : SharedBase ... @end;

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Shared Platform __ attribute __ ((swift_name(“Platform"))) @interface SharedPlatform : SharedBase @property (readonly) NSString *platform   @end;

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Common class Greeter { fun greet(): String { return "Hello ${Platform().platform}!" } }

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Common @interface SharedGreeting : SharedBase - (NSString *)greeting __ attribute __ ((swift_name("greeting()"))); @end;

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Android & iOS Shared Modules

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Use Case Hello   Android 29

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Shared Module Shared src commonMain androidMain iOSMain

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Android actual class Platform actual constructor() { actual val platform: String =   “Android ${android.os.Build.VERSION.SDK_INT}" }

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Hello   iOS 14.4 Use Case 9:41

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Shared Module Shared src commonMain androidMain iOSMain

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iOS import platform.UIKit.UIDevice actual class Platform actual constructor() { actual val platform: String = UIDevice.currentDevice.systemName() + " " +   UIDevice.currentDevice.systemVersion }

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iOS import platform.UIKit.UIDevice actual class Platform actual constructor() { actual val platform: String = UIDevice.currentDevice.systemName() + " " +   UIDevice.currentDevice.systemVersion }

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Summary ● How to build KMM project ● Shared Module Setup ● Inside Shared Framework

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CI Challenges

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Swift Package Manager

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Framework KMM Library

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Swift Package Manager KMM Library

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Multiplatform Swift Package ● Gradle plugin ● Generate XCFramework

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Multiplatform Swift Package id("com.chromaticnoise.multiplatform-swiftpackage") version "2.0.3"

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Multiplatform Swift Package multiplatformSwiftPackage { swiftToolsVersion(“5.5") targetPlatforms { iOS { v("13") } } }

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Multiplatform Swift Package ./gradlew createSwiftPackage

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KMM Library XCEFramework

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Projects/KMMProject Code ! Issues Pull Requests KMMLibrary.xcframework 1 commit 4c28f942 13 hours ago Package.swift KMMLibrary-1.0.zip README.md

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Choose Package Repository Search or enter package repository URL Name Last Updated Owner Projects(Github) KMMPackage Today 13:00 user

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Add Package to Project Choose package and targets Kind Add to Target KMMLibrary Library TestKMMLibrary Package Product

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Steps ● Create XCEFramework ● Consume using Swift Package Manager

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Build Automation

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KMM Library bdae142 .. main 50157a .. d89f145 .. f0ddfb ..

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bdae142 .. main 50157a .. d89f145 .. f0ddfb ..

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KMM Library Jar XCEFramework

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KMM Library Jar XCEFramework Artifactory

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Artifactory

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Build Automation ● Setup CI to create artifcats ● Use artifacts from repository like Artifactory

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API Design Challenges

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Flows

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Common fun getData(): Flow

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Android val flow = getData() flow.collect { }

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iOS getData( collector: T ## Kotlinx_coroutines_coreFlowCollector, completionHandler: (KotlinUnit?, Error?) -> Void )

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Common class CFlow internal constructor( val origin: Flow ) : Flow by origin { fun watch(block: (T) -> Unit) { } }

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Common class CFlow internal constructor( val origin: Flow ) : Flow by origin { fun watch(block: (T) -> Unit) { onEach { block(it) } launchIn(CoroutineScope( ... )) } }

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Common fun Flow.wrap(): CFlow = CFlow(this)

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iOS flow .wrap() .watch { data ->  }

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Building Kotlin Multiplatform Libraries ● Setting up KMM project ● CI Challenges ● API Design Challenges

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Thank You! www.codingwithmohit.com @heyitsmohit