Hi, have you met Kotlin Multiplatform? | Marca User Group

Kotlin Multiplatform is getting more and more hype every day, even if it’s still in alpha. We constantly read of new companies and teams that are trying KMP for experiments and production projects alike. And we’re left wondering: it safe to do so? Why picking KMP over any another cross-platform solution? How to approach it? And, most importantly, is it possible to start using it in existing projects?
In this talk, I’ll answer to these questions, clarifying all the doubts and making you ready to use and love Kotlin Multiplatform.

Transcript

1. Marco Gomiero Marca User Group Hi, have you met Kotlin Multiplatform?
2. Marca User Group - @marcoGomier Marco Gomiero Tech Lead @ Uniwhere Co-Lead @ GDG Venezia > Twitter: @marcoGomier > Github: prof18 > Website: marcogomiero.com
3. Marca User Group - @marcoGomier https://netflixtechblog.com/netflix-android-and-ios-studio-apps-kotlin-multiplatform-d6d4d8d25d23
4. Marca User Group - @marcoGomier <Your name here> https://kotlinlang.org/lp/mobile/case-studies/
5. Marca User Group - @marcoGomier https://twitter.com/piannaf/status/1206691901015044096
6. Marca User Group @marcoGomier So, what is Kotlin Multiplatform?
7. Marca User Group - @marcoGomier “Classic” Cross Platform Solutions React Native Flutter
8. Marca User Group - @marcoGomier Unify UI declaration across platforms
9. Marca User Group - @marcoGomier React Native: call native widgets through a “bridge”
10. Marca User Group - @marcoGomier Flutter: uses its own widget
11. Marca User Group - @marcoGomier • Cons: use of “middlemen”, custom widgets • Unifying UI declaration between platform is complicated • Different platforms have different patterns “Classic” Cross Platform Solutions
12. Marca User Group - @marcoGomier • Not about compiling all code for all platforms • Share as much [NO UI] code as possible Kotlin Multiplatform
13. Marca User Group - @marcoGomier Common Kotlin Kotlin/JVM Kotlin/JS Kotlin/Native Java Android Browser NodeJS Android NDK iOs macOS watchOS tvOS Linux Windows
14. Marca User Group - @marcoGomier Common Kotlin Kotlin/JVM Kotlin/JS Kotlin/Native Java Android Browser NodeJS Android NDK iOs macOS watchOS tvOS Linux Windows Mobile App
15. Marca User Group - @marcoGomier Common Kotlin Kotlin/JVM Kotlin/JS Kotlin/Native Java Android Browser NodeJS Android NDK iOs macOS watchOS tvOS Linux Windows Mobile & Desktop App + JVM Backend
16. Marca User Group - @marcoGomier Common Kotlin Kotlin/JVM Kotlin/JS Kotlin/Native Java Android Browser NodeJS Android NDK iOs macOS watchOS tvOS Linux Windows Full Stack JS App
17. Marca User Group - @marcoGomier • expect/actual mechanism • Declaration in common target and implementation in all specific targets • Works for functions, classes, interfaces, enumerations, properties, and annotations. Platform-specific APIs?
18. Marca User Group - @marcoGomier Common expect fun debugLog(tag: String, message: String)
19. Marca User Group - @marcoGomier Android expect fun debugLog(tag: String, message: String) import android.util.Log actual fun debugLog(tag: String, message: String) { Log.d(tag, message) }
20. Marca User Group - @marcoGomier iOs expect fun debugLog(tag: String, message: String) import platform.Foundation.NSLog actual fun debugLog(tag: String, message: String) { if (Platform.isDebugBinary) { NSLog("%s: %s", tag, message) } }
21. Marca User Group - @marcoGomier https://kotlinlang.org/lp/mobile/
22. Marca User Group - @marcoGomier https://kotlinlang.org/docs/mobile/home.html
23. Marca User Group - @marcoGomier Common Kotlin Kotlin/JVM Kotlin/Native Android iOs Mobile App
24. Marca User Group - @marcoGomier Common Kotlin Android App iOs App .aar Framework
25. Marca User Group - @marcoGomier Common Kotlin Android App iOs App .aar Framework Greenfield Project Same Repository
26. Marca User Group - @marcoGomier Same Repository
27. Marca User Group - @marcoGomier Android "// settings.gradle.kts include(":shared") "// build.gradle.kts implementation(project(":shared"))
28. Marca User Group - @marcoGomier iOs: packForXcode val packForXcode by tasks.creating(Sync"::class) { group = "build" val mode = System.getenv("CONFIGURATION") "?: "DEBUG" val sdkName = System.getenv("SDK_NAME") "?: "iphonesimulator" val targetName = "ios" + if (sdkName.startsWith("iphoneos")) "Arm64" else "X64" val framework = kotlin.targets.getByName<KotlinNativeTarget>(targetName).binaries.getFramework(mode) inputs.property("mode", mode) dependsOn(framework.linkTask) val targetDir = File(buildDir, "xcode-frameworks") from({ framework.outputDirectory }) into(targetDir) } tasks.getByName("build").dependsOn(packForXcode) Auto generated when creating a Kotlin Multiplatform mobile app
29. Marca User Group - @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.version}" } 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 plugin: shared.podspec https://kotlinlang.org/docs/reference/native/cocoapods.html
30. Marca User Group - @marcoGomier } 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 https://kotlinlang.org/docs/reference/native/cocoapods.html
31. Marca User Group - @marcoGomier iOs Project: Podfile pod 'shared', :path "=> '"../shared'
32. Marca User Group - @marcoGomier https://github.com/prof18/MoneyFlow
33. Marca User Group - @marcoGomier Common Kotlin Android App iOs App .aar Framework
34. Marca User Group - @marcoGomier Common Kotlin Android App iOs App .aar Framework Brownfield Project Android App Repository KMP Repository iOs App Repository
35. Marca User Group - @marcoGomier Android implementation("com.prof18.hn.foundation:hn-foundation-android:1.0.0")
36. Marca User Group - @marcoGomier iOs Project: Podfile pod 'HNFoundation', :git "=> "git@github.com:prof18/hn-foundation-cocoa.git", :tag "=> '1.0.0'
37. Marca User Group - @marcoGomier https://github.com/prof18/shared-hn-android-ios-backend
38. Marca User Group @marcoGomier How to publish: Android
39. Marca User Group - @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") } } } How to publish Android: Maven repository
40. Marca User Group @marcoGomier How to publish: iOs
41. Marca User Group - @marcoGomier Fat Framework
42. Marca User Group - @marcoGomier packForXcode Auto generated when creating a Kotlin Multiplatform mobile app val packForXcode by tasks.creating(Sync"::class) { group = "build" val mode = System.getenv("CONFIGURATION") "?: "DEBUG" val sdkName = System.getenv("SDK_NAME") "?: "iphonesimulator" val targetName = "ios" + if (sdkName.startsWith("iphoneos")) "Arm64" else "X64" val framework = kotlin.targets.getByName<KotlinNativeTarget>(targetName).binaries.getFramework(mode) inputs.property("mode", mode) dependsOn(framework.linkTask) val targetDir = File(buildDir, "xcode-frameworks") from({ framework.outputDirectory }) into(targetDir) } tasks.getByName("build").dependsOn(packForXcode)
43. Marca User Group - @marcoGomier 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 } ] CocoaPods plugin: shared.podspec https://kotlinlang.org/docs/reference/native/cocoapods.html
44. Marca User Group - @marcoGomier val libName = "HNFoundation" tasks { register("universalFrameworkDebug", org.jetbrains.kotlin.gradle.tasks.FatFrameworkTask"::class) { baseName = libName from( iosArm64().binaries.getFramework(libName, "Debug"), iosX64().binaries.getFramework(libName, "Debug") ) destinationDir = buildDir.resolve("$rootDir/"../"../hn-foundation-cocoa") group = libName description = "Create the debug framework for iOs" dependsOn("linkHNFoundationDebugFrameworkIosArm64") dependsOn("linkHNFoundationDebugFrameworkIosX64") } ""... } Custom Gradle Task: universalFrameworkDebug https://github.com/prof18/shared-hn-android-ios-backend/blob/master/hn-foundation/build.gradle.kts#L100
45. Marca User Group - @marcoGomier Custom Gradle Task: universalFrameworkDebug val libName = "HNFoundation" tasks { register("universalFrameworkDebug", org.jetbrains.kotlin.gradle.tasks.FatFrameworkTask"::class) { baseName = libName from( iosArm64().binaries.getFramework(libName, "Debug"), iosX64().binaries.getFramework(libName, "Debug") ) destinationDir = buildDir.resolve("$rootDir/"../"../hn-foundation-cocoa") group = libName description = "Create the debug framework for iOs" dependsOn("linkHNFoundationDebugFrameworkIosArm64") dependsOn("linkHNFoundationDebugFrameworkIosX64") } ""... } https://github.com/prof18/shared-hn-android-ios-backend/blob/master/hn-foundation/build.gradle.kts#L100
46. Marca User Group - @marcoGomier https://github.com/prof18/hn-foundation-cocoa/ CocoaPod Repository
48. https:"//guides.cocoapods.org/making/private-cocoapods.html
49. Automatic publishing task register("publishFramework") { description = "Publish iOs framework to the Cocoa Repo" project.exec { workingDir = File("$rootDir/"../"../hn-foundation-cocoa") commandLine("git", "checkout", "master").standardOutput } "// Create Release Framework for Xcode dependsOn("universalFrameworkRelease") "// Replace doLast { val dir = File("$rootDir/"../"../hn-foundation-cocoa/HNFoundation.podspec") val tempFile = File("$rootDir/"../"../hn-foundation-cocoa/HNFoundation.podspec.new") val reader = dir.bufferedReader() val writer = tempFile.bufferedWriter() var currentLine: String?
50. Marca User Group - @marcoGomier https://github.com/prof18/shared-hn-android-ios-backend/blob/master/hn-foundation/build.gradle.kts
51. Marca User Group @marcoGomier How to approach
52. Marca User Group - @marcoGomier How to approach • Existing projects • New projects
53. Marca User Group - @marcoGomier New Projects: Android Studio plugin
54. Marca User Group - @marcoGomier New Projects: Android Studio plugin
55. Marca User Group - @marcoGomier New Projects: Intellij Wizard
56. Marca User Group - @marcoGomier Marca User Group- @marcoGomier . └── kmm-project ├── androidApp ├── iosApp └── shared Photo by Ashkan Forouzani on Unsplash
57. Marca User Group - @marcoGomier Existing Project
58. Marca User Group - @marcoGomier Existing Projects: Intellij Wizard
59. Marca User Group - @marcoGomier You don’t have enough time for a big rewrite Photo by Ashkan Forouzani on Unsplash
60. Marca User Group - @marcoGomier . └── kmm-project ├── androidApp ├── iosApp └── shared Photo by Ashkan Forouzani on Unsplash Marca User Group- @marcoGomier
61. Marca User Group - @marcoGomier Photo by Erwan Hesry on Unsplash You can choose a little piece of tech stack to start with
62. Marca User Group - @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?
63. Marca User Group - @marcoGomier • DTOs • Common Models • Utility methods, aka `object Utils {}` Where to start?
64. Marca User Group - @marcoGomier Start little
65. Marca User Group - @marcoGomier Start little Go bigger then
66. Marca User Group - @marcoGomier Start little then go bigger • Validated the process with “little” effort • Next, go bigger and share more “features” For example the data layer, the network layer, etc
67. Marca User Group @marcoGomier Concurrency
68. Marca User Group - @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. Marca User Group - @marcoGomier Freeze the object to share it between threads
71. Marca User Group - @marcoGomier BaseDTO.kt open class BaseDTO { fun makeFrozen() { freeze() } }
72. Marca User Group - @marcoGomier https://github.com/touchlab/Stately
73. Marca User Group - @marcoGomier
74. Marca User Group - @marcoGomier https:"//www.youtube.com/watch?v=oxQ6e1VeH4M
75. Marca User Group - @marcoGomier
76. Marca User Group - @marcoGomier https:"//dev.to/kpgalligan/series/3739
77. Marca User Group - @marcoGomier • 1.4.1 "-> single thread on K/N • 1.4.1-native-mt "-> multithreaded version Coroutines https://kotlinlang.org/docs/mobile/concurrency-and-coroutines.html
78. Marca User Group - @marcoGomier https://blog.jetbrains.com/kotlin/2020/07/kotlin-native-memory-management-roadmap/
79. Marca User Group @marcoGomier Ecosystem
80. Marca User Group - @marcoGomier • Networking: Ktor • Persistence: SQLDelight, multiplatform-settings • Serialization: kotlinx.serialization • Dependency Injection: koin, Kodein-DI • Reactive: Reaktive • Date/Time: kotlinx-datetime (still experimental) Common Libraries
81. Marca User Group - @marcoGomier https://github.com/AAkira/Kotlin-Multiplatform-Libraries
82. Marca User Group - @marcoGomier https://github.com/touchlab/xcode-kotlin
83. Marca User Group - @marcoGomier
84. Marca User Group - @marcoGomier https://github.com/touchlab/CrashKiOS
85. Marca User Group - @marcoGomier
86. Marca User Group - @marcoGomier
87. Marca User Group - @marcoGomier https://github.com/getsentry/sentry-cocoa/issues/741
88. Marca User Group - @marcoGomier Jetpack Compose
89. Marca User Group - @marcoGomier https://www.jetbrains.com/lp/compose/
90. Marca User Group - @marcoGomier https://twitter.com/_gurupreet/status/1330118622895869956
91. Marca User Group - @marcoGomier https://twitter.com/joreilly/status/1324122305866457088
92. Marca User Group @marcoGomier Conclusions
93. Marca User Group - @marcoGomier • Kotlin Multiplatform "!= Cross Platform • Early adoption stage • It’s the future Conclusions
94. Marca User Group - @marcoGomier Join the Kotlin Slack https://kotlinlang.org/community/
95. Marco Gomiero Marca User Group Thank you! > Twitter: @marcoGomier > Github: prof18 > Website: marcogomiero.com