Introducing Kotlin Multiplatform in an existing project - DevFest Romania

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. Marco Gomiero DevFest Romania Introducing Kotlin Multiplatform in an existing project
2. DevFest Romania - @marcoGomier Marco Gomiero 👨💻 Android Engineer @ TIER 🛴 🇩🇪 🇮🇹 
 Google Developer Expert for Kotlin > Twitter: @marcoGomier 
 > Github: prof18 
 > Website: marcogomiero.com
3. DevFest Romania - @marcoGomier Kotlin Multiplatform
4. DevFest Romania - @marcoGomier Kotlin Multiplatform • Not about compiling all code for all platforms • Share as much [NO UI] code as possible
5. DevFest Romania - @marcoGomier Common Kotlin Kotlin/JVM Kotlin/JS Kotlin/Native Java Android Browser NodeJS Android NDK iOS macOS watchOS tvOS Linux Windows
6. DevFest Romania - @marcoGomier Common Kotlin Kotlin/JVM Kotlin/JS Kotlin/Native Java Android Browser NodeJS Android NDK iOS macOS watchOS tvOS Linux Windows Mobile App
7. DevFest Romania @marcoGomier New Project
8. DevFest Romania - @marcoGomier New Projects: Android Studio plugin
9. DevFest Romania - @marcoGomier New Projects: Android Studio plugin
10. DevFest Romania - @marcoGomier DevFest Romania - @marcoGomier . └── kmm-project ├── androidApp ├── iosApp └── shared Same Repository
11. DevFest Romania - @marcoGomier shared androidApp Gradle Module Android
12. DevFest Romania - @marcoGomier // settings.gradle.kts include(":shared") // build.gradle.kts implementation(project(":shared")) Android
13. DevFest Romania - @marcoGomier shared androidApp iosApp Gradle Module Framework iOS
14. DevFest Romania - @marcoGomier New Projects: Android Studio plugin
15. DevFest Romania - @marcoGomier embedAndSignAppleFrameworkForXcode https://blog.jetbrains.com/kotlin/2021/07/multiplatform-gradle-plugin-improved-for-connecting-kmm-modules/ packForXcode From Kotlin 1.5.20 iOS
16. DevFest Romania - @marcoGomier
17. DevFest Romania - @marcoGomier CocoaPods integration 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
18. DevFest Romania - @marcoGomier iOS Project: Podfile pod 'shared', :path => ' .. /shared'
19. DevFest Romania @marcoGomier Existing Project
20. DevFest Romania - @marcoGomier Photo by Ashkan Forouzani on Unsplash 🙅 shared androidApp iosApp Gradle Module Framework Same Repository
21. DevFest Romania - @marcoGomier Photo by Erwan Hesry on Unsplash 💡 Create a library!
22. DevFest Romania - @marcoGomier Photo by Erwan Hesry on Unsplash A little piece of tech stack to start with
23. DevFest Romania - @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?
24. DevFest Romania - @marcoGomier • DTOs • Common Models • Utility methods, aka `object Utils {}` • Analytics • . . . Where to start?
25. DevFest Romania - @marcoGomier Existing Projects: Intellij Wizard
26. DevFest Romania - @marcoGomier Common Kotlin Android App iOs App .aar Framework 
 Maven 
 Cocoa Repo
27. DevFest Romania - @marcoGomier Common Kotlin Android App iOs App .aar Framework 
 Maven 
 Cocoa Repo Android App Repository KMP Repository iOs App Repository
28. DevFest Romania @marcoGomier How to publish: Android
29. DevFest Romania - @marcoGomier https://github.com/prof18/shared-hn-android-ios-backend * based on a true story project
30. DevFest Romania - @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
31. DevFest Romania - @marcoGomier Publish the artifacts ./gradlew publish
32. DevFest Romania - @marcoGomier Publish the artifacts ./gradlew publish ./gradlew publishToMavenLocal
33. DevFest Romania - @marcoGomier Android implementation(“com.prof18.hn.foundation:hn-foundation-android:2.0.0")
34. DevFest Romania @marcoGomier How to publish: iOS
35. DevFest Romania - @marcoGomier 🥵
36. DevFest Romania - @marcoGomier embedAndSignAppleFrameworkForXcode packForXcode CocoaPods integration
37. DevFest Romania - @marcoGomier 🤔
38. DevFest Romania - @marcoGomier XCFramework
39. DevFest Romania - @marcoGomier NEW https://devstreaming-cdn.apple.com/videos/wwdc/2019/416h8485aty341c2/416/416_binary_frameworks_in_swift.pdf
40. DevFest Romania - @marcoGomier https://devstreaming-cdn.apple.com/videos/wwdc/2019/416h8485aty341c2/416/416_binary_frameworks_in_swift.pdf NEW iOS mac OS watch OS tvOS
41. DevFest Romania - @marcoGomier
42. DevFest Romania - @marcoGomier https: // developer.apple.com/videos/play/wwdc2019/416/
43. DevFest Romania - @marcoGomier XCFramework Official Support from Kotlin 1.5.30 https://kotlinlang.org/docs/whatsnew1530.html#support-for-xcframeworks
44. 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() } }
45. DevFest Romania - @marcoGomier XCFramework prior to Kotlin 1.5.30
46. DevFest Romania - @marcoGomier XCFramework prior to Kotlin 1.5.30 https: / / www.marcogomiero.com/posts/2021/build-xcframework-kmp/
47. DevFest Romania - @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) } } ... }
48. DevFest Romania - @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) } } ... }
49. DevFest Romania - @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) } } ... }
50. DevFest Romania - @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) } } ... }
51. DevFest Romania - @marcoGomier assemble${libName}XCFramework assemble${libName}DebugXCFramework assemble${libName}ReleaseXCFramework XCFramework: Gradle tasks
52. DevFest Romania - @marcoGomier . ├── build ├── XCFrameworks ├── debug │ └── LibraryName.xcframework └── release └── LibraryName.xcframework XCFramework
53. DevFest Romania - @marcoGomier https://github.com/prof18/hn-foundation-cocoa-xcframework CocoaPod Repository
54. DevFest Romania - @marcoGomier HNFoundation.podspec https://github.com/prof18/hn-foundation-cocoa-xcframework/blob/main/HNFoundation.podspec Pod :: Spec.new do |s| # ――― Spec Metadata ―――――――――――――――――――――――――――――――――――――――――――――――――――――――――― # # # These will help people to find your library, and whilst it # can feel like a chore to fill in it's definitely to your advantage. The # summary should be tweet-length, and the description more in depth. # s.name = "HNFoundation" s.version = "2.0.0" s.summary = "HNFoundation KMP library" s.homepage = "https: // github.com/prof18/hn-foundation-cocoa-xcframework" s.license = "Apache" s.author = { "Marco Gomiero" = > "mg@me.com" } s.vendored_frameworks = 'HNFoundation.xcframework' s.source = { :git => "git@github.com:prof18/hn-foundation-cocoa-xcframework", :tag => " #{ s.version}" } s.exclude_files = "Classes/Exclude" end
56. https: // guides.cocoapods.org/making/private-cocoapods.html
57. DevFest Romania - @marcoGomier iOs Project: Podfile # For develop releases: pod 'HNFoundation', :git => “git@github.com:prof18/hn-foundation-cocoa-xcframework.git", :branch = > 'develop'
58. DevFest Romania - @marcoGomier iOs Project: Podfile # For develop releases: pod 'HNFoundation', :git => “git@github.com:prof18/hn-foundation-cocoa-xcframework.git", :branch = > 'develop' # For stable releases pod 'HNFoundation', :git => “git@github.com:prof18/hn-foundation-cocoa-xcframework.git", :tag => ‘2.0.0'
59. register("publishDevFramework") { description = "Publish iOs framework to the Cocoa Repo" doFirst { project.exec { workingDir = File("$rootDir/ .. / .. /hn-foundation-cocoa-xcframework") commandLine("git", "checkout", "develop").standardOutput } } dependsOn("assemble${libName}DebugXCFramework") doLast { copy { from("$buildDir/XCFrameworks/debug") into("$rootDir/ .. / .. /hn-foundation-cocoa-xcframework") } .. .. https://github.com/prof18/shared-hn-android-ios-backend/blob/main/hn-foundation/build.gradle.kts#L110 Publish Dev Framework Task
60. DevFest Romania - @marcoGomier workingDir = File("$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())
61. DevFest Romania - @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("$rootDir/ .. / .. /hn-foundation-cocoa-xcframework")
62. DevFest Romania - @marcoGomier if (successful) { project.exec { workingDir = File("$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("$rootDir/ .. / .. /hn-foundation-cocoa-xcframework") commandLine("git", "push", "origin", "develop").standardOutput } }
63. https://github.com/prof18/shared-hn-android-ios-backend/blob/main/hn-foundation/build.gradle.kts#L177 Publish Release Framework Task register("publishFramework") { description = "Publish iOs framework to the Cocoa Repo" doFirst { project.exec { workingDir = File("$rootDir/ .. / .. /hn-foundation-cocoa-xcframework") commandLine("git", "checkout", "main").standardOutput } } dependsOn("assemble${libName}ReleaseXCFramework") doLast { copy { from("$buildDir/XCFrameworks/release") into("$rootDir/ .. / .. /hn-foundation-cocoa-xcframework") } .. ..
64. DevFest Romania - @marcoGomier project.exec { workingDir = File("$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/$libName.podspec.new") val reader = dir.bufferedReader() val writer = tempFile.bufferedWriter() var currentLine: String? while (reader.readLine().also { currLine -> currentLine = currLine } != null) { if (currentLine ?. startsWith("s.version") == true) {
65. DevFest Romania - @marcoGomier project.exec { workingDir = File("$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 } } } }
66. DevFest Romania - @marcoGomier 🎉
67. DevFest Romania @marcoGomier Concurrency
68. DevFest Romania - @marcoGomier • Kotlin/Native different from the JVM • One thread -> no problems, you can use mutable objects • Many thread - > only immutable objects Concurrency https://kotlinlang.org/docs/mobile/concurrency-overview.html
69. Uncaught Kotlin exception: kotlin.native.IncorrectDereferenceException: illegal attempt to access non-shared <object>@c2ddb8 from other thread
70. DevFest Romania - @marcoGomier 🥶 Freeze the object to share it between threads
71. DevFest Romania - @marcoGomier override fun deserialize(jsonString: String): NewsDTO { val newsDTO: NewsDTO = json.decodeFromString(jsonString) newsDTO.freeze() return newsDTO }
72. DevFest Romania - @marcoGomier https://blog.jetbrains.com/kotlin/2021/08/try-the-new-kotlin-native-memory-manager-development-preview/
73. DevFest Romania @marcoGomier Conclusions
74. DevFest Romania - @marcoGomier Faced [and resolved] difficulties • How to organise the project without a monorepo • How to effectively distribute the iOS framework
75. DevFest Romania - @marcoGomier Start little
76. DevFest Romania - @marcoGomier Start little Go bigger then
77. DevFest Romania - @marcoGomier Start little then go bigger • Validate the process with “little” effort • Then you can go bigger and share more “features” 

78. 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: / / www.youtube.com/watch?v=oxQ6e1VeH4M • https: / / dev.to/kpgalligan/series/3739 • https: / / blog.jetbrains.com/kotlin/2021/08/try-the-new-kotlin-native-memory-manager- development-preview/
79. Marco Gomiero DevFest Romania Thank you! > Twitter: @marcoGomier 
 > Github: prof18 
 > Website: marcogomiero.com