Introducing Kotlin Multiplatform in an existing project | Kotlin Dev Day Amsterdam

After discovering a new interesting technology or framework, you will probably start asking yourself how to integrate it into an existing project. That’s because, the possibility to start with a blank canvas is rare (not impossible, but rare).

This is also the case for Kotlin Multiplatform, and even though it is still in alpha, you can already start to use it in production applications.

In this talk, we will understand which part of the code can be a starting point for sharing, how to consume the shared code and how to structure an existing project to have an as smooth as possible integration.

Transcript

1. @marcoGomier Kotlin Dev Day Introducing Kotlin Multiplatform in an existing project Marco Gomiero 👨💻 Senior Android Engineer @ TIER 
 Google Developer Expert for Kotlin
2. Kotlin Dev Day - @marcoGomier Kotlin Multiplatform Share as much [NO UI] code as possible on different platforms
3. Kotlin Dev Day - @marcoGomier Common Kotlin Kotlin/JVM Kotlin/JS Kotlin/Native Java Android Browser NodeJS Android NDK iOS macOS watchOS tvOS Linux Windows
4. Kotlin Dev Day - @marcoGomier Common Kotlin Kotlin/JVM Kotlin/JS Kotlin/Native Java Android Browser NodeJS Android NDK iOS macOS watchOS tvOS Linux Windows Mobile App
5. Kotlin Dev Day @marcoGomier New Project
6. Kotlin Dev Day - @marcoGomier New Projects: Android Studio plugin
7. Kotlin Dev Day - @marcoGomier Kotlin Dev Day - @marcoGomier . └── kmm-project ├── androidApp ├── iosApp └── shared Same Repository
8. Kotlin Dev Day - @marcoGomier shared androidApp Gradle Module Android
9. Kotlin Dev Day - @marcoGomier // settings.gradle.kts include(":shared") // build.gradle.kts implementation(project(":shared")) Android
10. Kotlin Dev Day - @marcoGomier shared androidApp iosApp Gradle Module Framework iOS
11. Kotlin Dev Day - @marcoGomier New Projects: Android Studio plugin
12. Kotlin Dev Day - @marcoGomier embedAndSignAppleFrameworkForXcode https://blog.jetbrains.com/kotlin/2021/07/multiplatform-gradle-plugin-improved-for-connecting-kmm-modules/ Regular Framework
13. Kotlin Dev Day - @marcoGomier CocoaPods dependency manager https://kotlinlang.org/docs/reference/native/cocoapods.html Pod :: Spec.new do |spec| spec.name = 'shared' spec.version = '1.0-SNAPSHOT' spec.homepage = 'Link to a Kotlin/Native module homepage' spec.source = { :git => "Not Published", :tag = > "Cocoapods/ #{ spec.name} #{ spec.authors = '' spec.license = '' spec.summary = 'Some description for a Kotlin/Native module' 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
14. Kotlin Dev Day - @marcoGomier iOS Project: Podfile pod 'shared', :path => ' .. /shared'
15. Kotlin Dev Day @marcoGomier Existing Project
16. Kotlin Dev Day - @marcoGomier Photo by Ashkan Forouzani on Unsplash 🙅 shared androidApp iosApp Gradle Module Framework Same Repository
17. Kotlin Dev Day - @marcoGomier Photo by Erwan Hesry on Unsplash 💡 Create a library!
18. Kotlin Dev Day - @marcoGomier • Boring code to write multiple times • Code/feature that centralises the source of truth (i.e. a field is nullable or not) • Code/feature that can be gradually extracted Where to start?
19. Kotlin Dev Day - @marcoGomier • DTOs • Common Models • Utility methods, aka `object Utils {}` • Analytics • . . . Where to start?
20. Kotlin Dev Day - @marcoGomier Existing Projects: Intellij Wizard or Android Studio plugin
21. Kotlin Dev Day - @marcoGomier Common Kotlin Android App iOs App .aar Framework 
 Maven 
 Cocoa Repo
22. Kotlin Dev Day - @marcoGomier Common Kotlin Android App iOs App .aar Framework 
 Maven 
 Cocoa Repo Android App Repository KMP Repository iOs App Repository
23. Kotlin Dev Day @marcoGomier How to publish: Android
24. Kotlin Dev Day - @marcoGomier plugins { //.. . id("maven-publish") } group = "com.prof18.hn.foundation" version = "1.0" publishing { repositories { maven{ credentials { username = "username" password = "pwd" } url = url("https: // mymavenrepo.it") } } } Setup a Maven repository to share the artifacts: build.gradle.kts
25. Kotlin Dev Day - @marcoGomier Publish the artifacts ./gradlew publish
26. Kotlin Dev Day - @marcoGomier Publish the artifacts ./gradlew publish ./gradlew publishToMavenLocal
27. Kotlin Dev Day - @marcoGomier Android implementation(“com.prof18.hn.foundation:hn-foundation-android:2.0.0")
28. Kotlin Dev Day @marcoGomier How to publish: iOS
29. Kotlin Dev Day - @marcoGomier ❌ Regular Framework ❌ CocoaPods dependency manager
30. Kotlin Dev Day - @marcoGomier XCFramework
31. Kotlin Dev Day - @marcoGomier NEW https://developer.apple.com/videos/play/wwdc2019/416/ NEW iOS mac OS watch OS tvOS
32. Kotlin Dev Day - @marcoGomier XCFramework Official Support from Kotlin 1.5.30 https://kotlinlang.org/docs/whatsnew1530.html#support-for-xcframeworks
33. XCFramework prior to Kotlin 1.5.30 https://github.com/prof18/kmp-xcframework-sample/blob/pre-kotlin-1.5.30/build.gradle.kts#L86 register("buildReleaseXCFramework", Exec :: class.java) { description = "Create a Release XCFramework" dependsOn("link${libName}ReleaseFrameworkIosArm64") dependsOn("link${libName}ReleaseFrameworkIosX64") val arm64FrameworkPath = "$rootDir/build/bin/iosArm64/${libName}ReleaseFramework/${libName}.framework" val arm64DebugSymbolsPath = "$rootDir/build/bin/iosArm64/${libName}ReleaseFramework/${libName}.framework.dSYM" val x64FrameworkPath = "$rootDir/build/bin/iosX64/${libName}ReleaseFramework/${libName}.framework" val x64DebugSymbolsPath = "$rootDir/build/bin/iosX64/${libName}ReleaseFramework/${libName}.framework.dSYM" val xcFrameworkDest = File("$rootDir/ .. /kmp-xcframework-dest/$libName.xcframework") executable = "xcodebuild" args(mutableListOf<String>().apply { add("-create-xcframework") add("-output") add(xcFrameworkDest.path) // Real Device add("-framework") add(arm64FrameworkPath) add("-debug-symbols") add(arm64DebugSymbolsPath) // Simulator add("-framework") add(x64FrameworkPath) add("-debug-symbols") add(x64DebugSymbolsPath) }) doFirst { xcFrameworkDest.deleteRecursively() } }
34. Kotlin Dev Day - @marcoGomier XCFramework prior to Kotlin 1.5.30 https: / / www.marcogomiero.com/posts/2021/build-xcframework-kmp/
35. Kotlin Dev Day - @marcoGomier XCFramework: build.gradle.kts https://github.com/prof18/shared-hn-android-ios-backend/blob/main/hn-foundation/build.gradle.kts import org.jetbrains.kotlin.gradle.plugin.mpp.apple.XCFramework val libName = "LibraryName" kotlin { val xcFramework = XCFramework(libName) ios { binaries.framework(libName) { xcFramework.add(this) } } ... }
36. Kotlin Dev Day - @marcoGomier XCFramework: build.gradle.kts https://github.com/prof18/shared-hn-android-ios-backend/blob/main/hn-foundation/build.gradle.kts import org.jetbrains.kotlin.gradle.plugin.mpp.apple.XCFramework val libName = "LibraryName" kotlin { val xcFramework = XCFramework(libName) ios { binaries.framework(libName) { xcFramework.add(this) } } ... }
37. Kotlin Dev Day - @marcoGomier XCFramework: build.gradle.kts https://github.com/prof18/shared-hn-android-ios-backend/blob/main/hn-foundation/build.gradle.kts import org.jetbrains.kotlin.gradle.plugin.mpp.apple.XCFramework val libName = "LibraryName" kotlin { val xcFramework = XCFramework(libName) ios { binaries.framework(libName) { xcFramework.add(this) } } ... }
38. Kotlin Dev Day - @marcoGomier XCFramework: build.gradle.kts https://github.com/prof18/shared-hn-android-ios-backend/blob/main/hn-foundation/build.gradle.kts import org.jetbrains.kotlin.gradle.plugin.mpp.apple.XCFramework val libName = "LibraryName" kotlin { val xcFramework = XCFramework(libName) ios { binaries.framework(libName) { xcFramework.add(this) } } ... }
39. Kotlin Dev Day - @marcoGomier assemble${libName}XCFramework assemble${libName}DebugXCFramework assemble${libName}ReleaseXCFramework XCFramework: Gradle tasks
40. Kotlin Dev Day - @marcoGomier . ├── build ├── XCFrameworks ├── debug │ └── LibraryName.xcframework └── release └── LibraryName.xcframework XCFramework
41. Kotlin Dev Day - @marcoGomier https://github.com/prof18/hn-foundation-cocoa-xcframework CocoaPod Repository https://guides.cocoapods.org/making/private-cocoapods.html
42. Kotlin Dev Day - @marcoGomier iOs Project: Podfile # For develop releases: pod 'HNFoundation', :git => “git@github.com:prof18/hn-foundation-cocoa-xcframework.git", :branch = > 'develop' # For stable releases pod 'HNFoundation', :git => “git@github.com:prof18/hn-foundation-cocoa-xcframework.git", :tag => ‘2.0.0'
43. register("publishDevFramework") { description = "Publish iOs framework to the Cocoa Repo" doFirst { project.exec { workingDir = File("$rootDir/ .. / .. /hn-foundation-cocoa-xcframework") commandLine("git", "checkout", "develop").standardOutput } } dependsOn("assemble${libName}DebugXCFramework") doLast { copy { from("$buildDir/XCFrameworks/debug") into("$rootDir/ .. / .. /hn-foundation-cocoa-xcframework") } .. .. https://github.com/prof18/shared-hn-android-ios-backend/blob/main/hn-foundation/build.gradle.kts#L110 Publish Dev Framework Task
44. Kotlin Dev Day - @marcoGomier workingDir = File("$rootDir/ .. / .. /hn-foundation-cocoa-xcframework") commandLine("git", "checkout", "develop").standardOutput } } dependsOn("assemble${libName}DebugXCFramework") doLast { copy { from("$buildDir/XCFrameworks/debug") into("$rootDir/ .. / .. /hn-foundation-cocoa-xcframework") } val dir = File("$rootDir/ .. / .. /hn-foundation-cocoa-xcframework/$libName.podspec") val tempFile = File("$rootDir/ .. / .. /hn-foundation-cocoa-xcframework/$libName.podspec.new") val reader = dir.bufferedReader() val writer = tempFile.bufferedWriter() var currentLine: String? while (reader.readLine().also { currLine -> currentLine = currLine } != null) { if (currentLine ?. startsWith("s.version") == true) { writer.write("s.version = \"${libVersionName}\"" + System.lineSeparator())
45. Kotlin Dev Day - @marcoGomier into("$rootDir/ .. / .. /hn-foundation-cocoa-xcframework") } val dir = File("$rootDir/ .. / .. /hn-foundation-cocoa-xcframework/$libName.podspec") val tempFile = File("$rootDir/ .. / .. /hn-foundation-cocoa-xcframework/$libName.podspec.new") val reader = dir.bufferedReader() val writer = tempFile.bufferedWriter() var currentLine: String? while (reader.readLine().also { currLine -> currentLine = currLine } != null) { if (currentLine ?. startsWith("s.version") == true) { writer.write("s.version = \"${libVersionName}\"" + System.lineSeparator()) } else { writer.write(currentLine + System.lineSeparator()) } } writer.close() reader.close() val successful = tempFile.renameTo(dir) if (successful) { project.exec { workingDir = File("$rootDir/ .. / .. /hn-foundation-cocoa-xcframework")
46. Kotlin Dev Day - @marcoGomier if (successful) { project.exec { workingDir = File("$rootDir/ .. / .. /hn-foundation-cocoa-xcframework") commandLine("git", "add", ".").standardOutput } val dateFormatter = SimpleDateFormat("dd/MM/yyyy - HH:mm", Locale.getDefault()) project.exec { workingDir = File("$rootDir/ .. / .. /hn-foundation-cocoa-xcframework") commandLine( "git", "commit", "-m", "\"New dev release: ${libVersionName}-${dateFormatter.format(Date())}\"" ).standardOutput } project.exec { workingDir = File("$rootDir/ .. / .. /hn-foundation-cocoa-xcframework") commandLine("git", "push", "origin", "develop").standardOutput } }
47. https://github.com/prof18/shared-hn-android-ios-backend/blob/main/hn-foundation/build.gradle.kts#L177 Publish Release Framework Task register("publishFramework") { description = "Publish iOs framework to the Cocoa Repo" doFirst { project.exec { workingDir = File("$rootDir/ .. / .. /hn-foundation-cocoa-xcframework") commandLine("git", "checkout", "main").standardOutput } } dependsOn("assemble${libName}ReleaseXCFramework") doLast { copy { from("$buildDir/XCFrameworks/release") into("$rootDir/ .. / .. /hn-foundation-cocoa-xcframework") } .. ..
48. Kotlin Dev Day - @marcoGomier project.exec { workingDir = File("$rootDir/ .. / .. /hn-foundation-cocoa-xcframework") commandLine("git", "checkout", "main").standardOutput } } dependsOn("assemble${libName}ReleaseXCFramework") doLast { copy { from("$buildDir/XCFrameworks/release") into("$rootDir/ .. / .. /hn-foundation-cocoa-xcframework") } val dir = File("$rootDir/ .. / .. /hn-foundation-cocoa-xcframework/$libName.podspec") val tempFile = File("$rootDir/ .. / .. /hn-foundation-cocoa-xcframework/$libName.podspec.new") val reader = dir.bufferedReader() val writer = tempFile.bufferedWriter() var currentLine: String? while (reader.readLine().also { currLine -> currentLine = currLine } != null) { if (currentLine ?. startsWith("s.version") == true) {
49. Kotlin Dev Day - @marcoGomier project.exec { workingDir = File("$rootDir/ .. / .. /hn-foundation-cocoa-xcframework") commandLine("git", "add", ".").standardOutput } project.exec { workingDir = File("$rootDir/ .. / .. /hn-foundation-cocoa-xcframework") commandLine("git", "commit", "-m", "\"New release: ${libVersionName}\"").standardOu } project.exec { workingDir = File("$rootDir/ .. / .. /hn-foundation-cocoa-xcframework") commandLine("git", "tag", libVersionName).standardOutput } project.exec { workingDir = File("$rootDir/ .. / .. /hn-foundation-cocoa-xcframework") commandLine("git", "push", "origin", "main", " -- tags").standardOutput } } } }
50. Kotlin Dev Day - @marcoGomier 🎉
51. Kotlin Dev Day @marcoGomier Conclusions
52. Kotlin Dev Day - @marcoGomier Faced [and resolved] difficulties • How to organise the project without a monorepo • How to effectively distribute the iOS framework
53. Kotlin Dev Day - @marcoGomier Start little
54. Kotlin Dev Day - @marcoGomier Start little Go bigger then
55. Kotlin Dev Day - @marcoGomier Start little then go bigger • Validate the process with “little” effort • Then you can go bigger and share more “features” 

56. Kotlin Dev Day - @marcoGomier https://github.com/prof18/shared-hn-android-ios-backend * based on a true story project
57. Bibliography / Useful Links • https: // kotlinlang.org/lp/mobile/ • https: // www.marcogomiero.com/posts/2020/my-2cents-cross-platform/ • https: // giansegato.com/essays/a-technical-framework-for-early-stage-startups/ • https: // giansegato.com/essays/the-ebb-and-the-flow-of-product-development/ • https: // www.marcogomiero.com/posts/2021/build-xcframework-kmp/ • https: // www.marcogomiero.com/posts/2021/kmp-xcframework-official-support/ • https: // www.marcogomiero.com/posts/2020/kotlin-serialization-alamofire/ • https: // www.marcogomiero.com/posts/2021/kmp-existing-project/ • https: // developer.apple.com/videos/play/wwdc2019/416/ • https: // guides.cocoapods.org/making/private-cocoapods.html
58. @marcoGomier Kotlin Dev Day Thank you! > Twitter: @marcoGomier 
 > Github: prof18 
 > Website: marcogomiero.com Marco Gomiero 👨💻 Senior Android Engineer @ TIER 
 Google Developer Expert for Kotlin