Adopting Kotlin Multiplatform in Brownfield Applications - DCIT22

Presented at Droidcon Italy 2022

How can your team start sharing code with Kotlin Multiplatform? This is a simple question for a complex, and nuanced challenge.

Over the past year, our team has invested into Kotlin Multiplatform for both our iOS and Android applications. In this talk, we'll discuss our lessons learned and highlight how to solve key challenges including:
- Getting organizational buy in
- Configuring a multi-artifact build
- Building a CI/CD pipeline
- Publishing .jar, .aar, and Swift Packages
- Integration into brownfield applications
- Optimizing developer experience

By the end of this talk, you should have a clear technical and product roadmap for integrating Kotlin Multiplatform into your apps.

1. Nate Ebel @n8ebel Adopting Kotlin Multiplatform In Brown fi eld Applications
2. How can your team start sharing code using Kotlin Multiplatform?
3. 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
4. Kotlin Multiplatform Integration Roadmap
5. 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
6. Organizational Buy In
7. 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
8. “Let the problem define the solution” Tip #1
9. Our Problem “Analytics is a mess”
10. 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
11. Rationalizing analytics at Premise Can we codify this?
12. shared code for shared thinking
13. Perfect use case How to pitch KMP to the team?
14. iOS team suggested KMP fi rst
15. “Find an iOS team that wants to use Kotlin Multiplatform” Fake Tip #1
16. “Evaluate both technical, and human factors” Tip #2
17. 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
18. What next? How do we validate this KMP solution for shared analytics?
19. 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?
21. Create the project Answer technical questions Ship…something
22. What to ship first?
23. “Start small” Tip #3
24. 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
26. Building Our Kotlin Multiplatform Solution
27. “Think like library developers” Tip #4
29. 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?
30. Where will this new code live?
31. Where will this new code live? Greenfield KMP Project iOS Shared Android All projects live side by side in a single mono repo
32. 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
33. 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
34. Greenfield KMP Project Shared How to structure this new KMP project?
35. Greenfield KMP Project Shared How to structure this new KMP project?
36. Greenfield KMP Project Shared How to structure this new KMP project?
37. Greenfield KMP Project Shared How to structure this new KMP project? iosMain androidMain commonMain Are these the right targets for our use case?
38. Kotlin Multiplatform Targets iOS Javascript Linux JVM Android Mac
39. Greenfield KMP Project Shared Are these the right targets for our use case? iosMain androidMain commonMain
40. 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
41. Configuring Build Targets // analytics/build.gradle.kts plugins { kotlin(“multiplatform”) }
42. Configuring Build Targets // analytics/build.gradle.kts plugins { kotlin(“multiplatform”) } kotlin { jvm() iosX64() iosArm64() }
43. Configuring Build Targets kotlin { jvm() iosX64() iosArm64() }
44. Configuring Build Targets kotlin { jvm() iosX64() iosArm64() }
45. Configuring Build Targets kotlin { jvm() iosX64() iosArm64() sourceSets { val commonMain by getting val jvmMain by getting val iosX64Main by getting val iosArm64Main by getting } }
46. 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) } } }
47. 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?
48. 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?
49. Greenfield KMP Project Shared What if we want multiple multiplatform artifacts? iosMain commonMain jvmMain Imagine the N+1 solution of additional multiplatform features
50. Greenfield KMP Project What if we want multiple multiplatform artifacts? iosMain commonMain jvmMain Imagine the N+1 solution of additional multiplatform features
51. Greenfield KMP Project Analytics What if we want multiple multiplatform artifacts? iosMain commonMain jvmMain Imagine the N+1 solution of additional multiplatform features
52. Greenfield KMP Project Analytics What if we want multiple multiplatform artifacts? Imagine the N+1 solution of additional multiplatform features
53. Greenfield KMP Project Analytics What if we want multiple multiplatform artifacts? DTOs Networking Recommendations
54. Greenfield KMP Project Analytics What if we want multiple multiplatform artifacts? DTOs Networking Recommendations Android
55. Greenfield KMP Project Analytics What if we want multiple multiplatform artifacts? DTOs Networking Recommendations iOS
56. Greenfield KMP Project Analytics What if we want multiple multiplatform artifacts? DTOs Networking Recommendations iOS
57. Greenfield KMP Project Analytics What if we want multiple multiplatform artifacts? DTOs Networking Recommendations iOS Shared
58. Configuring a Composite Module Combine separate modules into 1 for iOS consumption // shared/build.gradle.kts plugins { kotlin(“multiplatform”) }
59. 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) }
60. 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 -> } }
61. 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 } } }
62. 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 } } }
63. 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 } } }
64. Configuring a Composite Module Combine separate modules into 1 for iOS consumption kotlin { . . . }
65. Configuring a Composite Module Combine separate modules into 1 for iOS consumption kotlin { . . . sourceSets { . . . iosMain by creating { dependencies { api(project(“:analytics”)) api(project(“:network”)) } } } }
66. 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?
67. 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?
68. Building Output Artifacts • Android / JVM • .jar / .aar • maven-publish plugin • iOS • XCFramework • Cocoapods • Swift Package Manager
69. Building JVM Output Artifacts / / analytics/build.gradle.kts plugins { kotlin(“multiplatform”) 
 id(“maven-publish”) }
70. Building Android Output Artifacts / / analytics/build.gradle.kts plugins { kotlin(“multiplatform”) id(“maven-publish”) id(“com.android.library”) }
71. Building Android Output Artifacts / / analytics/build.gradle.kts plugins { kotlin(“multiplatform”) id(“maven-publish”) id(“com.android.library”) }
72. Building Android Output Artifacts // analytics/build.gradle.kts plugins { … } kotlin { android { publishAllLibraryVariants() } }
73. Building JVM/Android Output Artifacts $ > > ./gradlew build publishToMavenLocal
74. Building iOS Swift Package / / shared/build.gradle.kts plugins { kotlin(“multiplatform”) id(“com.chromaticnoise.multiplatform-swiftpackage”) }
75. Building iOS Swift Package // shared/build.gradle.kts plugins { . . . }
76. Building iOS Swift Package // shared/build.gradle.kts plugins { . . . } multiplatformSwiftPackage { swiftToolsVersion(“5.3”) targetPlatforms { iOS { v(“13”) } } packageName(rootProject.name) distributionMode { local() } }
77. $ > > ./gradlew build createSwiftPakcage Building iOS Swift Package
78. 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?
79. 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?
80. Local Deployment for Android Consuming from mavenLocal() ./gradlew build publishToMavenLocal ~/.m2 build.gradle allProjects { repositories { mavenLocal() } } Android
81. 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
82. 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?
83. 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?
84. 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?
85. Building the Project with GitHub Actions checkout setup-java setup-xcode ./gradlew build ./gradlew createSwiftPackage
86. Deploying Android Artifacts / / analytics/build.gradle.kts plugins { id(“com.jfrog.artifactory”) }
87. Deploying Android Artifacts / / analytics/build.gradle.kts plugins { . . . }
88. Deploying Android Artifacts / / analytics/build.gradle.kts plugins { . . . }
89. Deploying Android Artifacts / / analytics/build.gradle.kts plugins { . . . } / / hand-wavy pseudocode artifactory { setContextUrl(“<your server url>”) }
90. Deploying Android Artifacts / / analytics/build.gradle.kts plugins { . . . } / / hand-wavy pseudocode artifactory { setContextUrl(“<your server url>”) }
91. Deploying Android Artifacts / / analytics/build.gradle.kts plugins { . . . } / / hand-wavy pseudocode artifactory { setContextUrl(“<your server url>”) repository { setProperty(“repoKey”, “<repo>”) setProperty(“username”, “<username>”) setProperty(“password”, “<password>”) setProperty(“maven”, true) } }
92. Deploying Android Artifacts / / hand-wavy pseudocode artifactory { setContextUrl(“<your server url>”) repository { setProperty(“repoKey”, “<repo>”) setProperty(“username”, “<username>”) setProperty(“password”, “<password>”) setProperty(“maven”, true) } }
93. Deploying Android Artifacts / / hand-wavy pseudocode artifactory { setContextUrl(“<your server url>”) repository { setProperty(“repoKey”, “<repo>”) setProperty(“username”, “<username>”) setProperty(“password”, “<password>”) setProperty(“maven”, true) } }
94. Deploying Android Artifacts / / hand-wavy pseudocode artifactory { setContextUrl(“<your server url>”) repository { setProperty(“repoKey”, “<repo>”) setProperty(“username”, “<username>”) setProperty(“password”, “<password>”) setProperty(“maven”, true) } defaults { invokeMethod(“publications”, arrayOf(“jvm”, “kotlinmultiplatform”)) } }
95. Consuming Android Artifact / / build.gradle.kts repositories { maven(url = “<your maven artifact server>”) } / / app/build.gradle.kts dependencies { implementation(“com.yourpackage.analytics:1.0.0”) }
96. Building the Project with GitHub Actions checkout setup-java setup-xcode ./gradlew build ./gradlew createSwiftPackage
97. Building the Project with GitHub Actions checkout setup-java setup-xcode ./gradlew build ./gradlew createSwiftPackage
98. Building the Project with GitHub Actions checkout setup-java setup-xcode ./gradlew build ./gradlew createSwiftPackage ./gradlew publishToArtifactory
99. Deploying Swift Packages shared.xcframework Package.swift premise/mobile-shared-swift-package .gitignore
100. 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
101. 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
102. Building the Project with GitHub Actions checkout setup-java setup-xcode ./gradlew build ./gradlew createSwiftPackage ./gradlew publishToArtifactory
103. 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
104. 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?
105. 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?
107. How are we using Kotlin Multiplatform today?
108. Kotlin Multiplatform at Premise Today Analytics Deeplinking Recommendations Security Performance Networking
109. Challenges Build Times Swift Package Generation API Usability Shared Ownership Swift Package Sync Time
110. • 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
111. • 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
112. • 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
113. • 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
114. • 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
115. “Collaborate from the beginning” Tip #5
116. 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
117. Takeaways
118. 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
119. 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
120. Thank You Nate Ebel @n8ebel