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Introducing Kotlin Multiplatform in an existing project - Android Worldwide

Introducing Kotlin Multiplatform in an existing project - Android Worldwide

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.

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Marco Gomiero

October 26, 2021
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  1. Marco Gomiero Android Worldwide Introducing Kotlin Multiplatform in an existing

    project
  2. Android Worldwide - @marcoGomier Marco Gomiero 👨💻 Android Engineer @

    TIER 🛴 🇩🇪 🇮🇹 
 Google Developer Expert for Kotlin > Twitter: @marcoGomier 
 > Github: prof18 
 > Website: marcogomiero.com
  3. Android Worldwide - @marcoGomier Kotlin Multiplatform

  4. Android Worldwide - @marcoGomier Kotlin Multiplatform • Not about compiling

    all code for all platforms • Share as much [NO UI] code as possible
  5. Android Worldwide - @marcoGomier Common Kotlin Kotlin/JVM Kotlin/JS Kotlin/Native Java

    Android Browser NodeJS Android NDK iOS macOS watchOS tvOS Linux Windows
  6. Android Worldwide - @marcoGomier Common Kotlin Kotlin/JVM Kotlin/JS Kotlin/Native Java

    Android Browser NodeJS Android NDK iOS macOS watchOS tvOS Linux Windows Mobile App
  7. Android Worldwide @marcoGomier New Project

  8. Android Worldwide - @marcoGomier New Projects: Android Studio plugin

  9. Android Worldwide - @marcoGomier New Projects: Android Studio plugin

  10. Android Worldwide - @marcoGomier Android Worldwide - @marcoGomier . └──

    kmm-project ├── androidApp ├── iosApp └── shared Same Repository
  11. Android Worldwide - @marcoGomier shared androidApp Gradle Module Android

  12. Android Worldwide - @marcoGomier // settings.gradle.kts include(":shared") // build.gradle.kts implementation(project(":shared"))

    Android
  13. Android Worldwide - @marcoGomier shared androidApp iosApp Gradle Module Framework

    iOS
  14. Android Worldwide - @marcoGomier New Projects: Android Studio plugin

  15. Android Worldwide - @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. Android Worldwide - @marcoGomier

  17. Android Worldwide - @marcoGomier 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 CocoaPods integration https://kotlinlang.org/docs/reference/native/cocoapods.html
  18. Android Worldwide - @marcoGomier iOS Project: Podfile pod 'shared', :path

    => ' .. /shared'
  19. Android Worldwide @marcoGomier Existing Project

  20. Android Worldwide - @marcoGomier Photo by Ashkan Forouzani on Unsplash

    🙅 shared androidApp iosApp Gradle Module Framework Same Repository
  21. Android Worldwide - @marcoGomier Photo by Erwan Hesry on Unsplash

    💡 Create a library!
  22. Android Worldwide - @marcoGomier Photo by Erwan Hesry on Unsplash

    A little piece of tech stack to start with
  23. Android Worldwide - @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. Android Worldwide - @marcoGomier • DTOs • Common Models •

    Utility methods, aka `object Utils {}` • Analytics • . . . Where to start?
  25. Android Worldwide - @marcoGomier Existing Projects: Intellij Wizard

  26. Android Worldwide - @marcoGomier Common Kotlin Android App iOs App

    .aar Framework 
 Maven 
 Cocoa Repo
  27. Android Worldwide - @marcoGomier Common Kotlin Android App iOs App

    .aar Framework 
 Maven 
 Cocoa Repo Android App Repository KMP Repository iOs App Repository
  28. Android Worldwide @marcoGomier How to publish: Android

  29. Android Worldwide - @marcoGomier https://github.com/prof18/shared-hn-android-ios-backend * based on a true

    story project
  30. Android Worldwide - @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. Android Worldwide - @marcoGomier Publish the artifacts ./gradlew publish

  32. Android Worldwide - @marcoGomier Publish the artifacts ./gradlew publish ./gradlew

    publishToMavenLocal
  33. Android Worldwide - @marcoGomier Android implementation(“com.prof18.hn.foundation:hn-foundation-android:2.0.0")

  34. Android Worldwide @marcoGomier How to publish: iOS

  35. Android Worldwide - @marcoGomier 🥵

  36. Android Worldwide - @marcoGomier embedAndSignAppleFrameworkForXcode packForXcode CocoaPods integration

  37. Android Worldwide - @marcoGomier 🤔

  38. Android Worldwide - @marcoGomier XCFramework

  39. Android Worldwide - @marcoGomier NEW https://devstreaming-cdn.apple.com/videos/wwdc/2019/416h8485aty341c2/416/416_binary_frameworks_in_swift.pdf

  40. Android Worldwide - @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. Android Worldwide - @marcoGomier

  42. Android Worldwide - @marcoGomier https: // developer.apple.com/videos/play/wwdc2019/416/

  43. Android Worldwide - @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. Android Worldwide - @marcoGomier XCFramework prior to Kotlin 1.5.30

  46. Android Worldwide - @marcoGomier XCFramework prior to Kotlin 1.5.30 https:

    / / www.marcogomiero.com/posts/2021/build-xcframework-kmp/
  47. Android Worldwide - @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. Android Worldwide - @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. Android Worldwide - @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. Android Worldwide - @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. Android Worldwide - @marcoGomier assemble${libName}XCFramework assemble${libName}DebugXCFramework assemble${libName}ReleaseXCFramework XCFramework: Gradle tasks

  52. Android Worldwide - @marcoGomier . ├── build ├── XCFrameworks ├──

    debug │ └── LibraryName.xcframework └── release └── LibraryName.xcframework XCFramework
  53. Android Worldwide - @marcoGomier https://github.com/prof18/hn-foundation-cocoa-xcframework CocoaPod Repository

  54. Android Worldwide - @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
  55. None
  56. https: // guides.cocoapods.org/making/private-cocoapods.html

  57. Android Worldwide - @marcoGomier iOs Project: Podfile # For develop

    releases: pod 'HNFoundation', :git => “git@github.com:prof18/hn-foundation-cocoa-xcframework.git", :branch = > 'develop'
  58. Android Worldwide - @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. Android Worldwide - @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. Android Worldwide - @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. Android Worldwide - @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. Android Worldwide - @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/$libName.podspec.new") val reader = dir.bufferedReader() val writer = tempFile.bufferedWriter() var currentLine: String? while (reader.readLine().also { currLine -> currentLine = currLine } != null) { if (currentLine ?. startsWith("s.version") == true) {
  65. Android Worldwide - @marcoGomier project.exec { workingDir = File("$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. Android Worldwide - @marcoGomier 🎉

  67. Android Worldwide @marcoGomier Concurrency

  68. Android Worldwide - @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. Android Worldwide - @marcoGomier 🥶 Freeze the object to share

    it between threads
  71. Android Worldwide - @marcoGomier override fun deserialize(jsonString: String): NewsDTO {

    val newsDTO: NewsDTO = json.decodeFromString(jsonString) newsDTO.freeze() return newsDTO }
  72. Android Worldwide - @marcoGomier https://blog.jetbrains.com/kotlin/2021/08/try-the-new-kotlin-native-memory-manager-development-preview/

  73. Android Worldwide @marcoGomier Conclusions

  74. Android Worldwide - @marcoGomier Faced [and resolved] difficulties • How

    to organise the project without a monorepo • How to effectively distribute the iOS framework
  75. Android Worldwide - @marcoGomier Start little

  76. Android Worldwide - @marcoGomier Start little Go bigger then

  77. Android Worldwide - @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 Android Worldwide Thank you! > Twitter: @marcoGomier 


    > Github: prof18 
 > Website: marcogomiero.com