Kotlin Multiplatform at Stable and Beyond (Android Makers 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 multiplatform tooling with Fleet, the experimental Amper project, and more!

For more, see:
https://zsmb.co/appearances/android-makers-2024-day1/

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. Build and runtime performance 📈
39. Gradle configuration cache support Build and runtime performance 📈
40. Gradle configuration cache support Build and runtime performance 📈 Incremental compilation of klib artifacts 🧪
41. Gradle configuration cache support Build and runtime performance 📈 Incremental compilation of klib artifacts 🧪 Kotlin/Native compiler cache management
42. 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
43. kotl.in/kmp-portal New
44. Kotlin-Swift interopedia kotl.in/interopedia New forked from hhru/kotlin-swift-interopedia
45. Currently via Objective-C
46. Work in progress via Objective-C
47. Demo kmp.jetbrains.com
48. Public Preview
53. Demo
54. Shared logic Swing Desktop logic Jetpack Compose Android logic SwiftUI iOS logic
55. Shared logic Swing Desktop logic Jetpack Compose Android logic SwiftUI iOS logic
56. jb.gg/compose Compose Multiplatform
57. Compose Multiplatform jb.gg/compose
58. @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 ) } } }
59. @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 ) } } }
60. Swing Desktop logic Jetpack Compose Android logic SwiftUI iOS logic Shared logic
61. Desktop logic Android logic iOS logic Shared logic Shared UI Compose Multiplatform
62. Desktop logic Android logic iOS logic Shared logic Shared UI Compose Multiplatform Swing Jetpack Compose SwiftUI
63. Latest developments Experimental
64. Latest developments Experimental Resources 1.6.0+
65. Latest developments Experimental Resources 1.6.0+ Lifecycle 2.8.0-beta01
66. Latest developments Experimental Resources 1.6.0+ Lifecycle 2.8.0-beta01 ViewModel 2.8.0-beta01
67. Latest developments Experimental Resources 1.6.0+ Lifecycle Navigation 2.8.0-beta01 2.8.0-alpha02 ViewModel 2.8.0-beta01
68. Resources org.jetbrains.compose.components:components-resources composeResources
69. Resources org.jetbrains.compose.components:components-resources drawable files font values composeResources
70. Resources org.jetbrains.compose.components:components-resources drawable files font values -fr -en-rUS -mdpi -xxhdpi -light -dark composeResources
71. Demo
72. Resources • Multi-module projects and library publication • Configuration options for generated file • Plural strings • Resource directories in multiple source sets New features coming in 1.6.10-beta02
73. Lifecycle org.jetbrains.androidx.lifecycle:lifecycle-common
74. 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
75. Demo
76. 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
77. ViewModelStoreOwner implementations Who owns the ViewModel?
78. ViewModelStoreOwner implementations 🗄 ComponentActivity ComposeView ComponentActivity Who owns the ViewModel?
79. ViewModelStoreOwner implementations 🗄 ComponentActivity ComposeView ComponentActivity Who owns the ViewModel?
80. ViewModelStoreOwner implementations SwiftUI 🗄 ComposeUIVC ComponentActivity ComposeUIViewController ComposeWindow CanvasBasedWindow Who owns the ViewModel?
81. ViewModelStoreOwner implementations SwiftUI 🗄 ComposeUIVC ComponentActivity ComposeUIViewController ComposeWindow CanvasBasedWindow Who owns the ViewModel?
82. ViewModelStoreOwner implementations NavBackStackEntry🗄 NavBackStackEntry🗄 NavBackStackEntry ComponentActivity ComposeUIViewController ComposeWindow CanvasBasedWindow Who owns the ViewModel? 🗄 ComposeUIVC
83. ViewModelStoreOwner implementations NavBackStackEntry🗄 NavBackStackEntry🗄 NavBackStackEntry ComponentActivity ComposeUIViewController ComposeWindow CanvasBasedWindow Who owns the ViewModel? 🗄 ComposeUIVC
84. ViewModelStoreOwner implementations YourCustomOwner 🗄 Provide your own! NavBackStackEntry ComponentActivity ComposeUIViewController ComposeWindow CanvasBasedWindow Who owns the ViewModel?
85. Navigation org.jetbrains.androidx.navigation:navigation-compose val navController: NavHostController = rememberNavController() NavHost( navController, startDestination = "list" ) { composable("list") { ListScreen(navController) } composable("detail/{objectId}") { backStackEntry -> val objectId = backStackEntry.arguments?.getString("objectId")?.toInt() DetailScreen(navController, objectId!!) } }
86. Demo
87. Amper Experimental jb.gg/amper
88. Demo
89. jb.gg/amper jb.gg/amper-slack jb.gg/amper-issues
90. Office hour: KMP 14:20 tomorrow Márton Braun John O'Reilly Marco Gomiero Baptiste Carlier Antoine Robiez
92. SOLD OUT
93. SOLD OUT kotlinconf.com/global youtube.com/kotlin
94. 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