Adopting Kotlin Multiplatform in Brownfield Applications - DCIT22

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Nate Ebel @n8ebel Adopting Kotlin Multiplatform In Brown fi eld Applications

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How can your team start sharing code using Kotlin Multiplatform?

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Where are we going? • How we got organizational buy in • How we solved key technical integration challenges • How we are using Kotlin Multiplatform today; and lessons learned

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Kotlin Multiplatform Integration Roadmap

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Kotlin Multiplatform at Premise Blog series • Kotlin Multiplatform at Premise • Kotlin Multiplatform Project Structure for Integration with Brown fi eld Applications • Building a CI Pipeline for Kotlin Multiplatform Mobile Using GitHub Actions

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Organizational Buy In

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About our team • 8 Android developers • 7 8 iOS developers • Android- fi rst feature development • Localized in 40 languages • Monthly active users in the hundreds of thousands

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“Let the problem define the solution” Tip #1

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Our Problem “Analytics is a mess”

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Rationalizing analytics at Premise • Enumerate standard types of analytics events • De fi ne rule patterns for each event type • Create shared documentation for Mobile team

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Rationalizing analytics at Premise Can we codify this?

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shared code for shared thinking

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Perfect use case How to pitch KMP to the team?

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iOS team suggested KMP fi rst

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“Find an iOS team that wants to use Kotlin Multiplatform” Fake Tip #1

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“Evaluate both technical, and human factors” Tip #2

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Why Kotlin Multiplatform? • Clear set of business rules to codify • Want to share that logic across iOS, Android (maybe backend) • Don’t need/want shared UI • Have engineers well versed in Kotlin • Have engineers comfortable with non-trivial Gradle builds • Want low-risk, medium/low-e ff ort integration into existing apps • Have engineers willing to prototype, learn, and educate

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What next? How do we validate this KMP solution for shared analytics?

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Primary questions How do we build and scale a KMP solution? • Where will this new code be stored? • How to structure a non-monorepo KMP project? • What multiplatform targets to choose? • How to distribute a multi-module artifact to iOS? • How to build output artifacts? • How to build, deploy, test locally? • How to ensure low cost deployment? • How to integrate into our existing iOS and Android projects?

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Create the project Answer technical questions Ship…something

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What to ship first?

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“Start small” Tip #3

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Validating KMP in production • Ship a single Kotlin Multiplatform String constant in production • Ensure no issues with development, CI/CD, or runtime in the wild

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Building Our Kotlin Multiplatform Solution

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“Think like library developers” Tip #4

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Where will this new code live?

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Where will this new code live? Greenfield KMP Project iOS Shared Android All projects live side by side in a single mono repo

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Where will this new code live? Brownfield iOS Project iOS Brownfield Android Project Android Greenfield KMP Project Shared Existing projects are untouched Shared code exists in a new, separate repo

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Where will this new code live? Brownfield iOS Project iOS Brownfield Android Project Android Greenfield KMP Project Shared Existing projects are untouched Shared code exists in a new, separate repo

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Greenfield KMP Project Shared How to structure this new KMP project?

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Greenfield KMP Project Shared How to structure this new KMP project?

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Greenfield KMP Project Shared How to structure this new KMP project?

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Greenfield KMP Project Shared How to structure this new KMP project? iosMain androidMain commonMain Are these the right targets for our use case?

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Kotlin Multiplatform Targets iOS Javascript Linux JVM Android Mac

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Greenfield KMP Project Shared Are these the right targets for our use case? iosMain androidMain commonMain

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Greenfield KMP Project Shared Are these the right targets for our use case? iosMain commonMain jvmMain Chose JVM over Android to support integration with JVM- based backend services

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Configuring Build Targets // analytics/build.gradle.kts plugins { kotlin(“multiplatform”) }

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Configuring Build Targets // analytics/build.gradle.kts plugins { kotlin(“multiplatform”) } kotlin { jvm() iosX64() iosArm64() }

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Configuring Build Targets kotlin { jvm() iosX64() iosArm64() }

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Configuring Build Targets kotlin { jvm() iosX64() iosArm64() }

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Configuring Build Targets kotlin { jvm() iosX64() iosArm64() sourceSets { val commonMain by getting val jvmMain by getting val iosX64Main by getting val iosArm64Main by getting } }

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Configuring Build Targets kotlin { jvm() iosX64() iosArm64() sourceSets { val commonMain by getting val jvmMain by getting val iosX64Main by getting val iosArm64Main by getting val iosMain by creating { dependsOn(commonMain) iosX64Main.dependsOn(this) iosArm64Main.dependsOn(this) } } }

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Greenfield KMP Project Shared What if we want multiple multiplatform artifacts? iosMain commonMain jvmMain Imagine the N+1 solution of additional multiplatform features

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Greenfield KMP Project What if we want multiple multiplatform artifacts? iosMain commonMain jvmMain Imagine the N+1 solution of additional multiplatform features

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Greenfield KMP Project Analytics What if we want multiple multiplatform artifacts? iosMain commonMain jvmMain Imagine the N+1 solution of additional multiplatform features

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Greenfield KMP Project Analytics What if we want multiple multiplatform artifacts? Imagine the N+1 solution of additional multiplatform features

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Greenfield KMP Project Analytics What if we want multiple multiplatform artifacts? DTOs Networking Recommendations

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Greenfield KMP Project Analytics What if we want multiple multiplatform artifacts? DTOs Networking Recommendations Android

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Greenfield KMP Project Analytics What if we want multiple multiplatform artifacts? DTOs Networking Recommendations iOS

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Greenfield KMP Project Analytics What if we want multiple multiplatform artifacts? DTOs Networking Recommendations iOS

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Greenfield KMP Project Analytics What if we want multiple multiplatform artifacts? DTOs Networking Recommendations iOS Shared

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Configuring a Composite Module Combine separate modules into 1 for iOS consumption // shared/build.gradle.kts plugins { kotlin(“multiplatform”) }

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Configuring a Composite Module Combine separate modules into 1 for iOS consumption // shared/build.gradle.kts plugins { kotlin(“multiplatform”) } kotlin { val xcf = XCFramework(rootProject.name) listOf(iosX64(), iosArm64(), iosSimulatorArm64()) .forEach { target -> target.binaries.framework { xcf.add(this) export(project(“:analytics”)) export(project(“:network”)) transitiveExport = true } } }

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Configuring a Composite Module Combine separate modules into 1 for iOS consumption kotlin { val xcf = XCFramework(rootProject.name) listOf(iosX64(), iosArm64(), iosSimulatorArm64()) .forEach { target -> target.binaries.framework { xcf.add(this) export(project(“:analytics”)) export(project(“:network”)) transitiveExport = true } } }

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Configuring a Composite Module Combine separate modules into 1 for iOS consumption kotlin { . . . }

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Configuring a Composite Module Combine separate modules into 1 for iOS consumption kotlin { . . . sourceSets { . . . iosMain by creating { dependencies { api(project(“:analytics”)) api(project(“:network”)) } } } }

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Building Output Artifacts • Android / JVM • .jar / .aar • maven-publish plugin • iOS • XCFramework • Cocoapods • Swift Package Manager

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Building JVM Output Artifacts / / analytics/build.gradle.kts plugins { kotlin(“multiplatform”)   id(“maven-publish”) }

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Building Android Output Artifacts / / analytics/build.gradle.kts plugins { kotlin(“multiplatform”) id(“maven-publish”) id(“com.android.library”) }

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Building Android Output Artifacts / / analytics/build.gradle.kts plugins { kotlin(“multiplatform”) id(“maven-publish”) id(“com.android.library”) }

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Building Android Output Artifacts // analytics/build.gradle.kts plugins { … } kotlin { android { publishAllLibraryVariants() } }

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Building JVM/Android Output Artifacts $ > > ./gradlew build publishToMavenLocal

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Building iOS Swift Package / / shared/build.gradle.kts plugins { kotlin(“multiplatform”) id(“com.chromaticnoise.multiplatform-swiftpackage”) }

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Building iOS Swift Package // shared/build.gradle.kts plugins { . . . }

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Building iOS Swift Package // shared/build.gradle.kts plugins { . . . } multiplatformSwiftPackage { swiftToolsVersion(“5.3”) targetPlatforms { iOS { v(“13”) } } packageName(rootProject.name) distributionMode { local() } }

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$ > > ./gradlew build createSwiftPakcage Building iOS Swift Package

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Local Deployment for Android Consuming from mavenLocal() ./gradlew build publishToMavenLocal ~/.m2 build.gradle allProjects { repositories { mavenLocal() } } Android

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Local Deployment for iOS Consuming local Swift Package ./gradlew build createSwiftPackage shared/output/swiftpackage iOS 1) add package dependency 2) add local 3) select shared/output/swiftpackage Xcode

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How do we ensure low cost deployment? Building a CI/CD pipeline • How to build the project in CI? • How to deploy the .jar and .aar fi les to internal Artifactory server? • How to deploy the Swift Package?

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Building the Project with GitHub Actions checkout setup-java setup-xcode ./gradlew build ./gradlew createSwiftPackage

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Deploying Android Artifacts / / analytics/build.gradle.kts plugins { id(“com.jfrog.artifactory”) }

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Deploying Android Artifacts / / analytics/build.gradle.kts plugins { . . . }

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Deploying Android Artifacts / / analytics/build.gradle.kts plugins { . . . }

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Deploying Android Artifacts / / analytics/build.gradle.kts plugins { . . . } / / hand-wavy pseudocode artifactory { setContextUrl(“”) }

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Deploying Android Artifacts / / analytics/build.gradle.kts plugins { . . . } / / hand-wavy pseudocode artifactory { setContextUrl(“”) }

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Deploying Android Artifacts / / analytics/build.gradle.kts plugins { . . . } / / hand-wavy pseudocode artifactory { setContextUrl(“”) repository { setProperty(“repoKey”, “”) setProperty(“username”, “”) setProperty(“password”, “”) setProperty(“maven”, true) } }

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Deploying Android Artifacts / / hand-wavy pseudocode artifactory { setContextUrl(“”) repository { setProperty(“repoKey”, “”) setProperty(“username”, “”) setProperty(“password”, “”) setProperty(“maven”, true) } }

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Consuming Android Artifact / / build.gradle.kts repositories { maven(url = “”) } / / app/build.gradle.kts dependencies { implementation(“com.yourpackage.analytics:1.0.0”) }

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Building the Project with GitHub Actions checkout setup-java setup-xcode ./gradlew build ./gradlew createSwiftPackage

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Building the Project with GitHub Actions checkout setup-java setup-xcode ./gradlew build ./gradlew createSwiftPackage

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Building the Project with GitHub Actions checkout setup-java setup-xcode ./gradlew build ./gradlew createSwiftPackage ./gradlew publishToArtifactory

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Deploying Swift Packages shared.xcframework Package.swift premise/mobile-shared-swift-package .gitignore

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Deploying Swift Packages shared.xcframework Package.swift premise/mobile-shared-swift-package .gitignore import PackageDescription let package = Package( name: “shared”, platforms: [ .iOS(.v13)], products: [ .library( name: “shared”, targets: [“shared”] ), ], targets: [ .binaryTarget( name: “shared”, path: “./shared.xcframework” ) ] ) / / Package.swift

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Consuming Swift Packages Xcode 1) Select Add framework or library 2) Select Add Package Dependency 3) Enter package url into search bar 4) Authenticate with GitHub 5) Select Add Package

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Building the Project with GitHub Actions checkout setup-java setup-xcode ./gradlew build ./gradlew createSwiftPackage ./gradlew publishToArtifactory

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Building the Project with GitHub Actions checkout setup-java setup-xcode ./gradlew build ./gradlew createSwiftPackage ./gradlew publishToArtifactory clone mobile-shared-swift-package commit, push & tag swiftpackage

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How are we using Kotlin Multiplatform today?

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Kotlin Multiplatform at Premise Today Analytics Deeplinking Recommendations Security Performance Networking

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Challenges Build Times Swift Package Generation API Usability Shared Ownership Swift Package Sync Time

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• Building XCFramework takes a long time • Build only what you need • Skip iOS targets if developing/iterating on Android • Reduce iOS targets if developing/iterating on speci fi c iOS target Build Times

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• multiplatform-swiftpackage hasn’t been updated with M1 support • Community forks available • Rolled our own custom Gradle task • Less fully-featured • Very focused on our exact needs Swift Package Generation

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• Syncing our Swift Package in XCode can take 30+ min • Publishing XCFrameworks to GitHub increases download size of repo • XCode doesn’t support shallow clone of the Swift Package repo • Update Swift Package to use a remote URL for framework download • Keeps large fi les out of the repo • Keeps XCode package sync fast Swift Package Sync Time

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• Kotlin features don’t always translate well to Objective-C • Enums, Sealed Classes, suspend functions, default parameters • Write or consume wrappers to improve api usability • Collaborate with iOS team to fi nd opportunities for improvement • Community work into improved Swift API generation API Usability

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• Majority of development, maintenance, and understanding consolidated in 1-2 members of the team • Encouraging shared ownership • Lunch-n-learns to build shared understanding • All Mobile developers can build both iOS and Android projects Shared Ownership

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“Collaborate from the beginning” Tip #5

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Collaborate From the Beginning • Get feedback from both iOS and Android teams early, and often • Validate new patterns across both platforms • Regularly build both projects to understand developer experience • Onboard new developers to shared project early on • Encourage contributions from all team members

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Takeaways

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Tips For Adopting Kotlin Multiplatform • “Let the problem de fi ne the solution” • “Evaluate both technical and human factors” • “Start small” • “Think like a library developer” • “Collaborate from the beginning” Tip #1 Tip #2 Tip #3 Tip #4 Tip #5