Hi, have you met Kotlin Multiplatform - ADI x GDG Pisa - Android Days: Day 1

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 ADI x GDG Pisa - Android Days Hi, have you met Kotlin Multiplatform?
2. ADI x GDG Pisa - Android Days - @marcoGomier Marco Gomiero 👨💻 Android Engineer @ TIER 🛴 🇩🇪 🇮🇹 
 Google Developer Expert for Kotlin 
 🍻 Co-Lead @ GDG Venezia > Twitter: @marcoGomier 
 > Github: prof18 
 > Website: marcogomiero.com
3. ADI x GDG Pisa - Android Days - @marcoGomier Kotlin Multiplatform
4. ADI x GDG Pisa - Android Days - @marcoGomier “Classic” Cross Platform Solutions React Native Flutter
5. ADI x GDG Pisa - Android Days - @marcoGomier Unify UI declaration across platforms
6. ADI x GDG Pisa - Android Days - @marcoGomier React Native: call native widgets through a “bridge”
7. ADI x GDG Pisa - Android Days - @marcoGomier Flutter: uses its own widget
8. ADI x GDG Pisa - Android Days - @marcoGomier • Cons: use of “middlemen”, custom widgets • Unifying UI declaration between platform is complicated • Different platforms have different patterns “Classic” Cross Platform Solutions
9. ADI x GDG Pisa - Android Days - @marcoGomier • Not about compiling all code for all platforms • Share as much [NO UI] code as possible Kotlin Multiplatform
10. ADI x GDG Pisa - Android Days - @marcoGomier Common Kotlin Kotlin/JVM Kotlin/JS Kotlin/Native Java Android Browser NodeJS Android NDK iOs macOS watchOS tvOS Linux Windows
11. ADI x GDG Pisa - Android Days - @marcoGomier Common Kotlin Kotlin/JVM Kotlin/JS Kotlin/Native Java Android Browser NodeJS Android NDK iOs macOS watchOS tvOS Linux Windows Mobile App
12. ADI x GDG Pisa - Android Days - @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
13. ADI x GDG Pisa - Android Days - @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
14. ADI x GDG Pisa - Android Days - @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?
15. ADI x GDG Pisa - Android Days - @marcoGomier Common expect fun debugLog(tag: String, message: String)
16. ADI x GDG Pisa - Android Days - @marcoGomier Android expect fun debugLog(tag: String, message: String) import android.util.Log actual fun debugLog(tag: String, message: String) { Log.d(tag, message) }
17. ADI x GDG Pisa - Android Days - @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) } }
18. ADI x GDG Pisa - Android Days - @marcoGomier Common Kotlin Kotlin/JVM Kotlin/JS Kotlin/Native Java Android Browser NodeJS Android NDK iOs macOS watchOS tvOS Linux Windows Mobile App
19. ADI x GDG Pisa - Android Days - @marcoGomier https://kotlinlang.org/lp/mobile/
20. GDG Pisa - Android Days @marcoGomier How it works: new project
21. ADI x GDG Pisa - Android Days - @marcoGomier shared androidApp Gradle Module Android
22. ADI x GDG Pisa - Android Days - @marcoGomier // settings.gradle.kts include(":shared") // build.gradle.kts implementation(project(":shared")) Android
23. ADI x GDG Pisa - Android Days - @marcoGomier shared androidApp iosApp Gradle Module Framework iOS
24. ADI x GDG Pisa - Android Days - @marcoGomier New Projects: Android Studio plugin
25. ADI x GDG Pisa - Android Days - @marcoGomier embedAndSignAppleFrameworkForXcode https://blog.jetbrains.com/kotlin/2021/07/multiplatform-gradle-plugin-improved-for-connecting-kmm-modules/ packForXcode From Kotlin 1.5.20 iOS
26. ADI x GDG Pisa - Android Days - @marcoGomier
27. ADI x GDG Pisa - Android Days - @marcoGomier New Projects: Android Studio plugin
28. ADI x GDG Pisa - Android Days - @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
29. ADI x GDG Pisa - Android Days - @marcoGomier iOS Project: Podfile pod 'shared', :path => ' .. /shared'
30. ADI x GDG Pisa - Android Days - @marcoGomier shared androidApp iosApp Gradle Module Framework Same Repository Same Repository
31. ADI x GDG Pisa - Android Days - @marcoGomier Conference Name - @marcoGomier . └── kmm-project ├── androidApp ├── iosApp └── shared Same Repository
32. ADI x GDG Pisa - Android Days - @marcoGomier https://github.com/prof18/MoneyFlow
33. GDG Pisa - Android Days @marcoGomier How it works: existing project
34. ADI x GDG Pisa - Android Days - @marcoGomier Conference Name - @marcoGomier Photo by Ashkan Forouzani on Unsplash 🙅 shared androidApp iosApp Gradle Module Framework Same Repository
35. ADI x GDG Pisa - Android Days - @marcoGomier Photo by Erwan Hesry on Unsplash 💡 Create a library!
36. ADI x GDG Pisa - Android Days - @marcoGomier Common Kotlin Android App iOs App .aar Framework 
 Maven 
 Cocoa Repo
37. ADI x GDG Pisa - Android Days - @marcoGomier Common Kotlin Android App iOs App .aar Framework 
 Maven 
 Cocoa Repo Android App Repository KMP Repository iOs App Repository
38. GDG Pisa - Android Days @marcoGomier How to publish: Android
39. ADI x GDG Pisa - Android Days - @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
40. ADI x GDG Pisa - Android Days - @marcoGomier Publish the artifacts ./gradlew publish
41. ADI x GDG Pisa - Android Days - @marcoGomier Publish the artifacts ./gradlew publish ./gradlew publishToMavenLocal
42. GDG Pisa - Android Days @marcoGomier How to publish: iOS
43. ADI x GDG Pisa - Android Days - @marcoGomier 🥵
44. ADI x GDG Pisa - Android Days - @marcoGomier embedAndSignAppleFrameworkForXcode packForXcode CocoaPods integration
45. ADI x GDG Pisa - Android Days - @marcoGomier 🤔
46. ADI x GDG Pisa - Android Days - @marcoGomier XCFramework
47. ADI x GDG Pisa - Android Days - @marcoGomier NEW https://devstreaming-cdn.apple.com/videos/wwdc/2019/416h8485aty341c2/416/416_binary_frameworks_in_swift.pdf
48. ADI x GDG Pisa - Android Days - @marcoGomier https://devstreaming-cdn.apple.com/videos/wwdc/2019/416h8485aty341c2/416/416_binary_frameworks_in_swift.pdf NEW iOS mac OS watch OS tvOS
49. ADI x GDG Pisa - Android Days - @marcoGomier XCFramework Official Support from Kotlin 1.5.30 https://kotlinlang.org/docs/whatsnew1530.html#support-for-xcframeworks
50. ADI x GDG Pisa - Android Days - @marcoGomier XCFramework prior to Kotlin 1.5.30
51. ADI x GDG Pisa - Android Days - @marcoGomier XCFramework prior to Kotlin 1.5.30 https: / / www.marcogomiero.com/posts/2021/build-xcframework-kmp/
52. ADI x GDG Pisa - Android Days - @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) } } ... }
53. ADI x GDG Pisa - Android Days - @marcoGomier assemble${libName}XCFramework assemble${libName}DebugXCFramework assemble${libName}ReleaseXCFramework XCFramework: Gradle tasks
54. ADI x GDG Pisa - Android Days - @marcoGomier . ├── build ├── XCFrameworks ├── debug │ └── LibraryName.xcframework └── release └── LibraryName.xcframework XCFramework
55. ADI x GDG Pisa - Android Days - @marcoGomier https://github.com/prof18/hn-foundation-cocoa-xcframework CocoaPod Repository
56. ADI x GDG Pisa - Android Days - @marcoGomier iOs Project: Podfile # For stable releases pod 'HNFoundation', :git => “git@github.com:prof18/hn-foundation-cocoa-xcframework.git", :tag => ‘2.0.0'
57. register("publishFramework") { description = "Publish iOs framework to the Cocoa Repo" doFirst { project.exec { workingDir = File("$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") } .. .. https://github.com/prof18/shared-hn-android-ios-backend/blob/main/hn-foundation/build.gradle.kts#L177 Publish Release XCFramework Task
58. ADI x GDG Pisa - Android Days - @marcoGomier
59. ADI x GDG Pisa - Android Days - @marcoGomier https: // www.marcogomiero.com/posts/2021/kmp-xcframework-official-support/
60. ADI x GDG Pisa - Android Days - @marcoGomier https://github.com/prof18/shared-hn-android-ios-backend * based on a true story project
61. GDG Pisa - Android Days @marcoGomier How to start: new project
62. ADI x GDG Pisa - Android Days - @marcoGomier New Projects: Android Studio plugin
63. ADI x GDG Pisa - Android Days - @marcoGomier New Projects: Android Studio plugin
64. ADI x GDG Pisa - Android Days - @marcoGomier New Projects: Android Studio plugin
65. GDG Pisa - Android Days @marcoGomier How to start: existing project
66. ADI x GDG Pisa - Android Days - @marcoGomier Existing Projects: Intellij Wizard
67. ADI x GDG Pisa - Android Days - @marcoGomier Photo by Erwan Hesry on Unsplash A little piece of tech stack to start with 💡 Create a library!
68. ADI x GDG Pisa - Android Days - @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?
69. ADI x GDG Pisa - Android Days - @marcoGomier • DTOs • Common Models • Utility methods, aka `object Utils {}` • Analytics • . . . Where to start?
70. ADI x GDG Pisa - Android Days - @marcoGomier Start little
71. ADI x GDG Pisa - Android Days - @marcoGomier Start little Go bigger then
72. ADI x GDG Pisa - Android Days - @marcoGomier Start little then go bigger • Validate the process with “little” effort • Then you can go bigger and share more “features” 

73. GDG Pisa - Android Days @marcoGomier Concurrency
74. ADI x GDG Pisa - Android Days - @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
75. Uncaught Kotlin exception: kotlin.native.IncorrectDereferenceException: illegal attempt to access non-shared <object>@c2ddb8 from other thread
76. ADI x GDG Pisa - Android Days - @marcoGomier 🥶 Freeze the object to share it between threads
77. ADI x GDG Pisa - Android Days - @marcoGomier override fun deserialize(jsonString: String): NewsDTO { val newsDTO: NewsDTO = json.decodeFromString(jsonString) newsDTO.freeze() return newsDTO }
78. ADI x GDG Pisa - Android Days - @marcoGomier https://blog.jetbrains.com/kotlin/2021/08/try-the-new-kotlin-native-memory-manager-development-preview/
79. GDG Pisa - Android Days @marcoGomier Ecosystem
80. ADI x GDG Pisa - Android Days - @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. ADI x GDG Pisa - Android Days - @marcoGomier https://github.com/AAkira/Kotlin-Multiplatform-Libraries
82. ADI x GDG Pisa - Android Days - @marcoGomier https://github.com/touchlab/xcode-kotlin
83. ADI x GDG Pisa - Android Days - @marcoGomier
84. ADI x GDG Pisa - Android Days - @marcoGomier Kotlin Multiplatform Mobile for AppCode https://blog.jetbrains.com/kotlin/2021/06/kmm-for-appcode/
85. ADI x GDG Pisa - Android Days - @marcoGomier https://github.com/touchlab/CrashKiOS
86. ADI x GDG Pisa - Android Days - @marcoGomier
87. ADI x GDG Pisa - Android Days - @marcoGomier
88. GDG Pisa - Android Days @marcoGomier Conclusions
89. ADI x GDG Pisa - Android Days - @marcoGomier • Kotlin Multiplatform ! = Cross Platform • Alpha stage, Beta spring 2022 • It’s the future Conclusions
90. Marco Gomiero ADI x GDG Pisa - Android Days Thank you! > Twitter: @marcoGomier 
 > Github: prof18 
 > Website: marcogomiero.com