Introducing Kotlin Multiplatform in an existing project | Kotlin Budapest Meetup - December

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

79. 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/
80. Marco Gomiero Kotlin Budapest Meetup Thank you! > Twitter: @marcoGomier 
 > Github: prof18 
 > Website: marcogomiero.com