Hi, have you met Kotlin Multiplatform | GDG Braunschweig

Kotlin Multiplatform is getting more and more hype every day. It started as an experimental technology, then alpha, beta and now it's on the path of becoming stable.

We constantly read of new companies and teams that are using KMP for experiments and production projects alike. And we're left wondering: why pick KMP over any other 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 these questions, clarifying all the doubts and making you ready to use and love Kotlin Multiplatform.

Transcript

1. 👨💻 Senior Android Engineer @ TIER 
 Google Developer Expert for Kotlin Marco Gomiero @marcoGomier Hi, have you met Kotlin Multiplatform?
2. @marcoGomier “Classic” Cross Platform Solutions • All-in approach • Everything is shared, UI included • Different platforms have different patterns
3. @marcoGomier Kotlin Multiplatform • Incremental approach • You choose what to share (even UI, if you want)
4. @marcoGomier Common Kotlin Kotlin/JVM Kotlin/JS Kotlin/Native JVM Android Browser NodeJS iOS macOS watchOS tvOS Linux Windows Supported Platforms
5. @marcoGomier Common Kotlin Kotlin/JVM Kotlin/JS Kotlin/Native JVM Android Browser NodeJS iOS macOS watchOS tvOS Linux Windows Mobile + JVM
6. @marcoGomier Common and Platform-specific code • Write regular Kotlin code in the common source set • Platform-specific code goes into platform source sets
7. @marcoGomier Platform-specific code • Expect/Actual
8. @marcoGomier Expect/Actual https://kotlinlang.org/docs/multiplatform-connect-to-apis.html
9. @marcoGomier Expect/Actual expect fun debugLog(tag: String, message: String)
10. @marcoGomier expect fun debugLog(tag: String, message: String) import android.util.Log actual fun debugLog(tag: String, message: String) { Log.d(tag, message) } import platform.Foundation.NSLog actual fun debugLog(tag: String, message: String) { if (Platform.isDebugBinary) { NSLog("%s: %s", tag, message) } }
11. @marcoGomier Platform-specific code • Expect/Actual • Interfaces
12. @marcoGomier Interfaces interface HtmlParser { fun getTextFromHTML(html: String): String? }
13. @marcoGomier import org.jsoup.Jsoup internal class JvmHtmlParser : HtmlParser { override fun getTextFromHTML(html: String): String? { return try { val doc = Jsoup.parse(html) doc.text() } catch (e: Throwable) { null } } } import shared import SwiftSoup class IosHtmlParser: HtmlParser { func getTextFromHTML(html: String) -> String? { do { let doc: Document = try SwiftSoup.parse(html) return try doc.text() } catch { return nil } } } interface HtmlParser { fun getTextFromHTML(html: String): String? }
14. @marcoGomier Platform-specific code • Expect/Actual • Interfaces • Prefer interfaces, if possible
15. @marcoGomier How it works?
16. @marcoGomier shared androidApp .aar Android
17. @marcoGomier shared androidApp iosApp .aar Framework iOS Android
18. @marcoGomier XCFramework
19. @marcoGomier NEW https://devstreaming-cdn.apple.com/videos/wwdc/2019/416h8485aty341c2/416/416_binary_frameworks_in_swift.pdf
20. @marcoGomier https://devstreaming-cdn.apple.com/videos/wwdc/2019/416h8485aty341c2/416/416_binary_frameworks_in_swift.pdf NEW iOS mac OS watch OS tvOS
21. @marcoGomier Kotlin -> Obj-c -> Swift
22. @marcoGomier when (appState.newsState) { is NewsState.Loading -> { progressBar.visibility = View.VISIBLE ... } is NewsState.Error -> { errorButton.visibility = View.VISIBLE errorMessage.visibility = View.VISIBLE ... } is NewsState.Success -> { progressBar.visibility = View.GONE errorMessage.visibility = View.GONE recyclerView.visibility = View.VISIBLE ... } }
23. @marcoGomier Some gotchas • No namespaces • No default parameters • Enums are not Swift-friendly (no values) • Sealed classes are simple classes • Coroutines and Flows
24. @marcoGomier https://github.com/rickclephas/KMP-NativeCoroutines
25. @marcoGomier https://github.com/touchlab/SKIE
26. @marcoGomier https://github.com/icerockdev/moko-kswift
27. @marcoGomier Make it a team effort
28. @marcoGomier https://medium.com/@aoriani/list/writing-swiftfriendly-kotlin-multiplatform-apis-c51c2b317fce
29. @marcoGomier New projects
30. @marcoGomier Create a new app project
31. @marcoGomier
32. @marcoGomier
33. @marcoGomier
34. @marcoGomier shared androidApp Gradle Module Android
35. @marcoGomier // settings.gradle.kts include(":shared") // build.gradle.kts implementation(project(":shared")) Android
36. @marcoGomier shared androidApp iosApp Gradle Module Framework iOS Android
37. @marcoGomier Regular Framework
38. @marcoGomier Create a new app project
39. @marcoGomier CocoaPods integration https://kotlinlang.org/docs/reference/native/cocoapods.html Pod::Spec.new do |spec| spec.name = 'shared' spec.version = '1.0' spec.homepage = 'Link to the Shared Module homepage' spec.source = { :http=> ''} spec.authors = '' spec.license = '' spec.summary = 'Some description for the Shared Module' spec.vendored_frameworks = 'build/cocoapods/framework/shared.framework' spec.libraries = 'c++' spec.ios.deployment_target = '14.1' spec.pod_target_xcconfig = { 'KOTLIN_PROJECT_PATH' => ':shared', 'PRODUCT_MODULE_NAME' => 'shared', } spec.script_phases = [ { :name => 'Build shared', :execution_position => :before_compile, :shell_path => '/bin/sh', :script => <<-SCRIPT if [ "YES" = "$OVERRIDE_KOTLIN_BUILD_IDE_SUPPORTED" ]; then echo "Skipping Gradle build task invocation due to OVERRIDE_KOTLIN_BUILD_IDE_SUPPORTED environment exit 0 fi set -ev REPO_ROOT="$PODS_TARGET_SRCROOT" "$REPO_ROOT/../gradlew" -p "$REPO_ROOT" $KOTLIN_PROJECT_PATH:syncFramework \ -Pkotlin.native.cocoapods.platform=$PLATFORM_NAME \ -Pkotlin.native.cocoapods.archs="$ARCHS" \ -Pkotlin.native.cocoapods.configuration="$CONFIGURATION" SCRIPT } ] end
40. @marcoGomier iOSApp: Podfile https://kotlinlang.org/docs/reference/native/cocoapods.html target 'iosApp' do use_frameworks! platform :ios, '14.1' pod 'shared', :path => '../shared' end
41. @marcoGomier shared androidApp iosApp Gradle Module Framework iOS Android
42. @marcoGomier shared androidApp iosApp Framework Same Repository Gradle Module
43. @marcoGomier Existing projects
44. @marcoGomier 🙅 shared androidApp iosApp Gradle Module Framework Same Repository Existing projects
45. @marcoGomier Create a new library project
46. @marcoGomier
47. @marcoGomier Common Kotlin Android App iOS App .aar XCFramework 

48. @marcoGomier Common Kotlin Android App iOS App .aar XCFramework 
 Android App Repository KMP Repository iOs App Repository
49. @marcoGomier How to publish: Android
50. @marcoGomier Setup a Maven repository to share the artifacts: build.gradle.kts plugins { //... id("maven-publish") } group = "com.prof18.hn.foundation" version = "1.0" publishing { repositories { maven { credentials { username = "username" password = "pwd" } url = URI.create("https://mymavenrepo.it") } } }
51. @marcoGomier Publish the artifacts ./gradlew publish
52. @marcoGomier Publish the artifacts ./gradlew publish ./gradlew publishToMavenLocal
53. @marcoGomier How to publish: iOS
54. @marcoGomier 🥵
55. @marcoGomier XCFramework
56. @marcoGomier Build an XCFramework https://kotlinlang.org/docs/multiplatform-build-native-binaries.html#build-xcframeworks import org.jetbrains.kotlin.gradle.plugin.mpp.apple.XCFramework val libName = "LibraryName" kotlin { val xcFramework = XCFramework(libName) ios { binaries.framework(libName) { xcFramework.add(this) } } ... }
57. @marcoGomier XCFramework: Gradle tasks assemble${libName}XCFramework assemble${libName}DebugXCFramework assemble${libName}ReleaseXCFramework
58. @marcoGomier Build an XCFramework
59. @marcoGomier https://github.com/touchlab/KMMBridge
60. @marcoGomier https://github.com/prof18/kmp-framework-bundler
61. @marcoGomier Where to start
62. @marcoGomier shared androidApp iosApp Gradle Module Framework Same Repository New projects
63. @marcoGomier 🙅 shared androidApp iosApp Gradle Module Framework Same Repository Existing projects
64. @marcoGomier 💡 Create a library!
65. @marcoGomier • Boring code to write multiple times • Code/feature that centralizes the source of truth • Code/feature that can be gradually extracted Where to start?
66. @marcoGomier • DTOs • Common Models • Utility methods • Analytics • . . . Where to start?
67. @marcoGomier Start little
68. @marcoGomier Start little Go bigger then
69. @marcoGomier Start little then go bigger • Validate the process with “little” effort • Then you can go bigger and share more “features” 

70. @marcoGomier Ecosystem
71. @marcoGomier • Networking: Ktor, Apollo • Persistence: SQLDelight, multiplatform-settings, Realm • Serialization: kotlinx.serialization • Dependency Injection: Koin, Kodein, kotlin-inject • Asynchronous: Coroutines, Reaktive • Date/Time: kotlinx-datetime • Logging: Kermit, Napier Common Libraries And much more ...
72. @marcoGomier https://github.com/AAkira/Kotlin-Multiplatform-Libraries https://github.com/terrakok/kmp-awesome
73. @marcoGomier https://github.com/touchlab/xcode-kotlin
74. @marcoGomier https://github.com/touchlab/xcode-kotlin
75. @marcoGomier https://github.com/touchlab/xcode-kotlin
76. @marcoGomier https://github.com/touchlab/CrashKiOS
77. @marcoGomier https://github.com/touchlab/CrashKiOS
78. @marcoGomier Conclusions
79. @marcoGomier • Kotlin Multiplatform ! = Cross Platform • Beta stage, Stable late 2023 Conclusions
80. @marcoGomier https://www.droidcon.com/2023/07/31/10-myths-about-crossplatform-mobile-development-with-kotlin/
81. @marcoGomier • Kotlin Multiplatform ! = Cross Platform • Beta stage, Stable late 2023 • It’s the future • It’s a joint and team approach Conclusions
82. Bibliography / Useful Links • https: // kotlinlang.org/docs/multiplatform.html • https: // kotlinlang.org/docs/native-overview.html • https: // kotlinlang.org/docs/js-overview.html • https: // kotlinlang.org/docs/multiplatform-share-on-platforms.html • https: // kotlinlang.org/docs/multiplatform-connect-to-apis.html • https: // devstreaming-cdn.apple.com/videos/wwdc/2019/416h8485aty341c2/416/416_binary_frameworks_in_swift.pdf • https: // developer.apple.com/videos/play/wwdc2019/416/ • https: // medium.com/@aoriani/list/writing-swiftfriendly-kotlin-multiplatform-apis-c51c2b317fce • https: // kotlinlang.org/docs/native-objc-interop.html • https: // speakerdeck.com/kpgalligan/kotlinconf-2023-kotlin-mobile-multiplatform-for-teams • https: // speakerdeck.com/kpgalligan/sdk-design-and-publishing-for-kotlin-multiplatform-mobile • https: // kotlinlang.org/docs/reference/native/cocoapods.html • https: // kotlinlang.org/docs/multiplatform-build-native-binaries.html#build-xcframeworks • https: // github.com/touchlab/KMMBridge • https: // github.com/prof18/kmp-framework-bundler • https: // github.com/touchlab/xcode-kotlin • https: // github.com/terrakok/kmp-awesome • https: // github.com/AAkira/Kotlin-Multiplatform-Libraries • https: // github.com/touchlab/CrashKiOS • https: // www.droidcon.com/2023/07/31/10-myths-about-crossplatform-mobile-development-with-kotlin/
83. @marcoGomier Thank you! > Twitter: @marcoGomier 
 > Github: prof18 
 > Website: marcogomiero.com 
 > Mastodon: androiddev.social/@marcogom 👨💻 Senior Android Engineer @ TIER 
 Google Developer Expert for Kotlin Marco Gomiero