Kotlin Multiplatform at Stable and Beyond (Kotlin Vienna, October 2024)

Kotlin Multiplatform became stable last year, making it ready for production use for anyone looking to share code between platforms. In this talk, we’ll take a look at what that announcement means for Kotlin Multiplatform, and how the technology is evolving now, beyond the stable release.

You’ll hear about UI sharing with Compose Multiplatform, the latest of Kotlin multiplatform tooling, the experimental Amper project, and more!

More details: https://zsmb.co/talks/kmp-at-stable-and-beyond/

Transcript

1. Kotlin Multiplatform at Stable and Beyond Márton Braun Developer Advocate
2. iOS Android Desktop Web Server
3. iOS Android Desktop Web Server
4. iOS Android Desktop +
5. .kt .kt .kt .kt Android Desktop iOS Common
6. .kt .kt .kt .kt Android Desktop iOS Common
7. .kt .kt .kt Android Desktop iOS Common class Person(val name: String, var age: Int) fun greet(person: Person) { println("Hello, ${person.name}") }
8. .kt .kt .kt Android Desktop iOS Common fun List<Person>.duplicates(): Map<String, Int> { return map { it.name.substringBefore(" ") } .groupingBy { it } .eachCount() .filter { (name, count) -> count > 1 } }
9. Android Desktop iOS actual Common expect actual actual
10. Android Desktop iOS Common expect actual actual actual
11. Android Desktop iOS Common fun getPlatform(): String expect actual actual actual
12. Android Desktop iOS Common fun getPlatform(): String fun getPlatform(): String = "Java ${System.getProperty("java.version")}" expect actual actual actual
13. Android iOS fun getPlatform(): String = "Android ${Build.VERSION.SDK_INT}" actual actual Common fun getPlatform(): String expect Desktop fun getPlatform(): String = "Java ${System.getProperty("java.version")}" actual
14. Android iOS fun getPlatform(): String = "iOS ${UIDevice.currentDevice.systemVersion}" fun getPlatform(): String = "Android ${Build.VERSION.SDK_INT}" actual actual Common fun getPlatform(): String expect Desktop fun getPlatform(): String = "Java ${System.getProperty("java.version")}" actual
15. Android Desktop iOS Common fun getPlatform(): String fun getPlatform(): String = "Java ${System.getProperty("java.version")}" fun getPlatform(): String = "iOS ${UIDevice.currentDevice.systemVersion}" fun getPlatform(): String = "Android ${Build.VERSION.SDK_INT}" expect actual actual actual
16. Multiplatform libraries
17. github.com/terrakok/kmp-awesome
18. .kt .kt .kt Android Desktop iOS Common import io.ktor.client.* suspend fun loadHtml(): String { val client = HttpClient() val response = client.get("https://kotlinlang.org") return response.body<String>() }
19. Shared logic
20. Shared logic Swing Desktop logic Jetpack Compose Android logic SwiftUI iOS logic
21. Shared logic Swing Desktop logic Jetpack Compose Android logic SwiftUI iOS logic
22. Shared logic Swing Desktop logic Jetpack Compose Android logic SwiftUI iOS logic
23. 2019 2020 2021 2022 2023 2024 2025 Experimental ➟
24. Alpha 2019 2020 2021 2022 2023 2024 2025
25. Beta 2019 2020 2021 2022 2023 2024 2025
26. Stable 2019 2020 2021 2022 2023 2024 2025
27. Stable 2019 2020 2021 2022 2023 2024 2025
28. Compiler support Language features Library APIs Build tooling IDE support Strict compatibility guarantees kotl.in/kmp-stability
29. Configuring targets kotlin { androidTarget() iosArm64() iosSimulatorArm64() sourceSets { val commonMain by getting val iosMain by creating { dependsOn(commonMain) } val iosArm64Main by creating { dependsOn(iosMain) } val iosSimulatorArm64Main by creating { dependsOn(iosMain) } } }
30. Configuring targets kotlin { androidTarget() iosArm64() iosSimulatorArm64() sourceSets { val commonMain by getting val iosMain by creating { dependsOn(commonMain) } val iosArm64Main by creating { dependsOn(iosMain) } val iosSimulatorArm64Main by creating { dependsOn(iosMain) } } }
31. Configuring targets kotlin { androidTarget() iosArm64() iosSimulatorArm64() }
32. common jvm android native js androidNative apple mingw linux iosArm64 iosSimulatorArm64 mingwX64 android_arm64 ... ios macos tvos watchos Configuring targets kotlin { androidTarget() iosArm64() iosSimulatorArm64() } iosArm64 iosX64 iosSimulatorArm64 iosArm64 iosSimulatorArm64 iosArm64 iosSimulatorArm64 iosArm64 iosSimulatorArm64
33. common jvm android native js androidNative apple mingw linux iosArm64 iosSimulatorArm64 mingwX64 android_arm64 ... ios macos tvos watchos Configuring targets kotlin { androidTarget() iosArm64() iosSimulatorArm64() } iosX64 iosArm64 iosSimulatorArm64 iosArm64 iosSimulatorArm64 iosArm64 iosSimulatorArm64 iosArm64 iosSimulatorArm64
34. common jvm android native js androidNative apple mingw linux iosArm64 iosSimulatorArm64 mingwX64 android_arm64 ... ios macos tvos watchos Configuring targets kotlin { androidTarget() iosArm64() iosSimulatorArm64() iosX64 iosArm64 iosSimulatorArm64 iosArm64 iosSimulatorArm64 iosArm64 iosSimulatorArm64 iosArm64 iosSimulatorArm64 }
35. Configuring targets kotlin { androidTarget() iosArm64() iosSimulatorArm64() sourceSets { } } m m o c
36. Configuring targets kotlin { androidTarget() iosArm64() iosSimulatorArm64() sourceSets { commonMain } }
37. Configuring targets kotlin { androidTarget() iosArm64() iosSimulatorArm64() sourceSets { commonMain.dependencies { implementation(libs.ktor.client.core) } androidMain.dependencies { implementation(libs.ktor.client.okhttp) } iosMain.dependencies { implementation(libs.ktor.client.darwin) } } }
38. Gradle configuration cache support Build and runtime performance 📈 Incremental compilation of klib artifacts 🧪 New custom memory allocator in Kotlin/Native Kotlin/Native compiler cache management
39. kotl.in/kmp-portal
40. Kotlin-Swift interopedia kotl.in/interopedia forked from hhru/kotlin-swift-interopedia
41. Currently via Objective-C
42. Work in progress via Objective-C
43. Work in progress github.com/Kotlin/swift-export-sample
44. Demo kmp.jetbrains.com
45. Public Preview
50. Demo
51. Shared logic Swing Desktop logic Jetpack Compose Android logic SwiftUI iOS logic
52. Shared logic Swing Desktop logic Jetpack Compose Android logic SwiftUI iOS logic
53. jb.gg/compose Compose Multiplatform
54. Compose Multiplatform jb.gg/compose
55. @Composable fun SquaresGalleryView( images: List<PictureData>, selectedImage: PictureData, onSelect: (PictureData) -> Unit, ) { LazyVerticalGrid( modifier = Modifier.padding(top = 4.dp), columns = GridCells.Adaptive(minSize = 130.dp), verticalArrangement = Arrangement.spacedBy(1.dp), horizontalArrangement = Arrangement.spacedBy(1.dp) ) { itemsIndexed(images) { _, picture -> SquareThumbnail( picture = picture, onClick = { onSelect(picture) }, isHighlighted = selectedImage === picture ) } } }
56. @Composable fun SquaresGalleryView( images: List<PictureData>, selectedImage: PictureData, onSelect: (PictureData) -> Unit, ) { LazyVerticalGrid( modifier = Modifier.padding(top = 4.dp), columns = GridCells.Adaptive(minSize = 130.dp), verticalArrangement = Arrangement.spacedBy(1.dp), horizontalArrangement = Arrangement.spacedBy(1.dp) ) { itemsIndexed(images) { _, picture -> SquareThumbnail( picture = picture, onClick = { onSelect(picture) }, isHighlighted = selectedImage === picture ) } } }
57. Swing Desktop logic Jetpack Compose Android logic SwiftUI iOS logic Shared logic
58. Desktop logic Android logic iOS logic Shared logic Shared UI Compose Multiplatform
59. Desktop logic Android logic iOS logic Shared logic Shared UI Compose Multiplatform Swing Jetpack Compose SwiftUI
60. Latest developments Resources 1.6.0+ Lifecycle Navigation 2.8.0 2.8.0-alpha09 ViewModel 2.8.0
61. Resources org.jetbrains.compose.components:components-resources composeResources
62. Resources org.jetbrains.compose.components:components-resources drawable files font values composeResources
63. Resources org.jetbrains.compose.components:components-resources drawable files font values -de -en-rUS -mdpi -xxhdpi -light -dark composeResources
64. Demo
65. Resources • Multi-module projects and library publication • Configuration options for generated file • Plural strings • Resource directories in multiple source sets
66. Lifecycle org.jetbrains.androidx.lifecycle:lifecycle-common
67. Lifecycle on Desktop org.jetbrains.androidx.lifecycle:lifecycle-runtime-compose Swing listener callbacks Lifecycle event Lifecycle state change windowLostFocus ON_PAUSE RESUMED → STARTED windowGainedFocus ON_RESUME STARTED → RESUMED windowIconified ON_STOP STARTED → CREATED windowDeiconified ON_START CREATED → STARTED dispose ON_DESTROY CREATED → DESTROYED
68. Demo
69. ViewModel org.jetbrains.androidx.lifecycle:lifecycle-viewmodel-compose package androidx.lifecycle public abstract class ViewModel { protected open fun onCleared() public fun addCloseable(key: String, closeable: AutoCloseable) public open fun addCloseable(closeable: AutoCloseable) } public val ViewModel.viewModelScope: CoroutineScope
70. ViewModelStoreOwner implementations Who owns the ViewModel?
71. ViewModelStoreOwner implementations 🗄 ComponentActivity ComposeView ComponentActivity Who owns the ViewModel?
72. ViewModelStoreOwner implementations 🗄 ComponentActivity ComposeView ComponentActivity Who owns the ViewModel?
73. ViewModelStoreOwner implementations SwiftUI 🗄 ComposeUIVC ComponentActivity ComposeUIViewController ComposeWindow CanvasBasedWindow Who owns the ViewModel?
74. ViewModelStoreOwner implementations SwiftUI 🗄 ComposeUIVC ComponentActivity ComposeUIViewController ComposeWindow CanvasBasedWindow Who owns the ViewModel?
75. ViewModelStoreOwner implementations NavBackStackEntry🗄 NavBackStackEntry🗄 NavBackStackEntry ComponentActivity ComposeUIViewController ComposeWindow CanvasBasedWindow Who owns the ViewModel? 🗄 ComposeUIVC
76. ViewModelStoreOwner implementations NavBackStackEntry🗄 NavBackStackEntry🗄 NavBackStackEntry ComponentActivity ComposeUIViewController ComposeWindow CanvasBasedWindow Who owns the ViewModel? 🗄 ComposeUIVC
77. ViewModelStoreOwner implementations YourCustomOwner 🗄 Provide your own! NavBackStackEntry ComponentActivity ComposeUIViewController ComposeWindow CanvasBasedWindow Who owns the ViewModel?
78. Navigation org.jetbrains.androidx.navigation:navigation-compose val controller = rememberNavController() NavHost(navController = controller, startDestination = "list") { composable("list") { ListScreen( navToDetails = { objectId -> controller.navigate("details/$objectId" } ) } composable("details/{objectId}") { backStack -> DetailScreen( objectId = backStack.arguments?.getString("objectId"), navBack = { controller.popBackStack() } ) } } )
79. Navigation org.jetbrains.androidx.navigation:navigation-compose val controller = rememberNavController() NavHost(navController = controller, startDestination = "list") { composable("list") { ListScreen( navToDetails = { objectId -> controller.navigate("details/$objectId" } ) } composable("details/{objectId}") { backStack -> DetailScreen( objectId = backStack.arguments?.getString("objectId"), navBack = { controller.popBackStack() } ) } } )
80. Navigation org.jetbrains.androidx.navigation:navigation-compose val controller = rememberNavController() NavHost(navController = controller, startDestination = ListDestination) { composable<ListDestination> { ListScreen( navToDetails = { objectId -> controller.navigate(DetailDestination(objectId) } ) } composable<DetailDestination> { backStack -> DetailScreen( objectId = backStack.toRoute<DetailDestination>().objectId, navBack = { controller.popBackStack() } ) } } )
81. Demo
82. Amper Experimental jb.gg/amper
83. Demo
84. jb.gg/amper jb.gg/amper-slack jb.gg/amper-issues jb.gg/amper-blog
85. Kotlin Multiplatform jb.gg/kmp Compose Multiplatform jb.gg/compose jb.gg/compose-resources jb.gg/compose-navigation jb.gg/compose-lifecycle Fleet jb.gg/fleet Amper jb.gg/amper Kotlin Multiplatform at Stable and Beyond zsmb.co/talks Márton Braun @zsmb13@androiddev.social