Going Multiplatform with Your Android App (Android Makers 2026)

Existing Android apps are in a great position to expand into Kotlin Multiplatform: you might already be using patterns, libraries, and APIs that work on more platforms than just Android. With Compose Multiplatform, you can build an app with a fully shared Kotlin codebase, targeting iOS, desktop, and even the web!

In this talk, we’ll look at how you can migrate an existing Android app to multiplatform. As this can be a significant engineering effort for an existing, well-established app, we’ll also discuss how to plan and organize the required changes, and how to adopt KMP incrementally across your codebase without disrupting day-to-day development.

Transcript

1. Márton Braun Developer Advocate Going Multiplatform with Your Android App
2. What we’re doing today Strategy Modernizing Preparing for Multiplatform Going Multiplatform 2
3. What we’re doing today Strategy Modernizing Preparing for Multiplatform Going Multiplatform 3
4. What we’re doing today 4 Strategy Modernizing Preparing for Multiplatform Going Multiplatform
5. What we’re doing today 5 Strategy Modernizing Preparing for Multiplatform Going Multiplatform
6. What we’re doing today 6 Strategy Modernizing Preparing for Multiplatform Going Multiplatform
7. Strategy
8. Incremental migration 8
10. Bottom up UI Presentation Business logic Data UI Presentation Business logic Data 10
11. Bottom up UI Presentation Business logic Data UI Presentation Business logic Data 11
12. Bottom up UI Presentation Business logic Data UI Presentation Business logic 12
13. Bottom up UI Presentation Business logic Data UI Presentation 13
14. Bottom up UI Presentation Business logic Data UI 14
15. Bottom up UI Presentation Business logic Data 15
16. Quick start 16
17. Quick start 17
18. Quick start 18
19. Quick start 19
20. Quick start 20
21. Quick start 21
22. Quick start 22
23. Quick start 23
24. Quick start 24
25. Quick start 25
26. Quick start • Ship almost immediately 26
27. Quick start • Ship almost immediately • Nontrivial moves 27
28. Quick start • Ship almost immediately • Nontrivial moves • Fragmentation Retrofit RxJava Glide Dagger kapt Ktor Coroutines Coil Koin KSP 28
29. Quick start • Ship almost immediately • Nontrivial moves • Fragmentation • Structural changes ? 29
30. In-place migration 30
31. In-place migration Complete scope 31
32. In-place migration Complete scope Initial scope 32
33. In-place migration Complete scope Initial scope 33
34. Doing the work Complete scope Initial scope 0% 100% 34
35. Doing the work Complete scope Initial scope 0% 100% 35
36. Doing the work Complete scope Initial scope 0% 100% 36
37. Doing the work Complete scope Initial scope 0% 100% 37
38. Doing the work Complete scope Initial scope 0% 100% 38
39. Doing the work Complete scope Initial scope 0% 100% 39
40. Doing the work Complete scope Initial scope 0% 100% 40
41. Axes of migration 🪓 Modules Complete scope Initial scope Steps 41
42. Axes of migration 🪓 Modules Complete scope Initial scope Steps 42
43. Axes of migration 🪓 Modules Complete scope Initial scope Steps 43
44. Axes of migration 🪓 Modules Complete scope Initial scope Steps 44
45. Axes of migration 🪓 Modules Complete scope Initial scope Steps 45
46. Axes of migration 🪓 Modules Complete scope Initial scope Steps 46
47. Axes of migration 🪓 Steps Modules Complete scope Initial scope 47
48. On pacing yourself 48
49. One step at a time Steps 49
50. Modernizing
51. Migrate from Java to Kotlin • Docs on kotlinlang.org • J2K converter in Intell" IDEA • AI tools kotl.in/java-to-kotlin kotl.in/agent-skills 51
52. Groovy to Kotlin DSL 53
53. kapt to KSP 54
54. kapt to KSP 56
55. kapt to KSP // Android dependencies { ksp("androidx.room3:room3-compiler:3.0.0-alpha01") } // Kotlin Multiplatform dependencies { add("kspAndroid","androidx.room3:room3-compiler:3.0.0-alpha01") add("kspIosArm64","androidx.room3:room3-compiler:3.0.0-alpha01") add("kspJvm","androidx.room3:room3-compiler:3.0.0-alpha01") add("kspJs","androidx.room3:room3-compiler:3.0.0-alpha01") add("kspWasmJs","androidx.room3:room3-compiler:3.0.0-alpha01") } 57
56. Update ALL the dependencies • Gradle • Android Gradle Plugin • Kotlin • Jetpack Compose • … kotl.in/kmp-compat kotl.in/cmp-compat kotl.in/gradle/agp9 58
57. Adopt coroutines kotl.in/coroutines-docs 60
58. Coroutine interop libraries github.com/Kotlin/kotlinx.coroutines/tree/master/reactive 61
59. Views to Jetpack Compose 62
60. Views to Jetpack Compose 63
61. Preparing for Multiplatform 64
62. Moving to multiplatform APIs commonMain androidMain iosMain jvmMain webMain 65
63. A few common replacements JDK, Android APIs Kotlin standard library Moshi, Jackson, Gson kotlinx.serialization java.time kotlinx-datetime OkHttp Ktor Retrofit Ktorfit kotlinx-rpc (Preview) gRPC JUnit kotlin.test, kotest SQLite SQLDelight Dagger, Anvil Metro Glide Coil 66
64. Already good to go Kotlin standard library kotlinx.serialization kotlinx-datetime Ktor Ktorfit kotlinx-rpc (Preview) kotlin.test, kotest SQLDelight Metro Coil Room Compose DataStore Koin Apollo GraphQL Arrow 67
65. Find KMP libraries Klibs.io 68
66. Err on the side of multiplatform. 69
67. Handling the rest kotl.in/platform-apis 70
68. Handling the rest commonMain androidMain iosMain expect fun getPlatform actual fun getPlatform actual fun getPlatform 71
69. Handling the rest commonMain androidMain iosMain expect fun getPlatformId(): String actual fun getPlatformId(): String = !!... actual fun getPlatformId(): String = !!... 72
70. Handling the rest commonMain androidMain iosMain interface Platform { !!... } fun init(platform: Platform) class AndroidPlatform Platform { !!... } class IosPlatform : Platform { !!... } : 73
71. Handling the rest commonMain androidMain iosMain interface Platform { !!... } fun init(platform: Platform) class AndroidPlatform( context: Context ) Platform { !!... } class IosPlatform : Platform { !!... } : 74
72. Preparing for AGP 9 KMP requirements kotl.in/agp9-blog 75
73. Preparing for AGP 9 KMP requirements Variants / Native builds 76
74. Preparing for AGP 9 KMP requirements Variants / Native builds 77
75. Preparing for AGP 9 KMP requirements Variants / Native builds 78
76. Preparing for AGP 9 KMP requirements Variants / Native builds 79
77. Preparing for AGP 9 KMP requirements Variants / Native builds androidMain 80
78. Preparing for AGP 9 KMP requirements 81
79. Going Multiplatform
80. Setting up the KMP plugin 83
81. Setting up the KMP plugin 84
82. Setting up the KMP plugin (for Android) 85
83. Setting up the KMP plugin (for Android) Change plugins Move dependencies Move sources Add AGP 9 opt-ins 86
84. Setting up the KMP plugin (for Android) Set up Compose Multiplatform Configure previews Use multiplatform resources Change plugins Move dependencies Move sources Add AGP 9 opt-ins 87
85. Setting up the KMP plugin plugins { alias(libs.plugins.android.library) alias(libs.plugins.kotlin.multiplatform) alias(libs.plugins.android.multiplatform.library) } - + + 88
86. Setting up the KMP plugin android { namespace = "com.example.mylibrary" compileSdk = 36 defaultConfig { minSdk = 24 } compileOptions { sourceCompatibility = VERSION_11 targetCompatibility = VERSION_11 } buildFeatures { compose = true } } 89
87. Setting up the KMP plugin kotlin { android { namespace = "com.example.mylibrary" compileSdk = 36 defaultConfig { minSdk = 24 } compileOptions { sourceCompatibility = VERSION_11 targetCompatibility = VERSION_11 } buildFeatures { compose = true } } } 90
88. Setting up the KMP plugin kotlin { androidLibrary { namespace = "com.example.mylibrary" compileSdk = 36 defaultConfig { minSdk = 24 } compileOptions { sourceCompatibility = VERSION_11 targetCompatibility = VERSION_11 } buildFeatures { compose = true } } } 91
89. Setting up the KMP plugin kotlin { android { namespace = "com.example.mylibrary" compileSdk = 36 defaultConfig { minSdk = 24 } compileOptions { sourceCompatibility = VERSION_11 targetCompatibility = VERSION_11 } buildFeatures { compose = true } } } 92
90. Setting up the KMP plugin kotlin { android { namespace = "com.example.mylibrary" compileSdk = 36 defaultConfig { minSdk = 24 } compileOptions { sourceCompatibility = VERSION_11 targetCompatibility = VERSION_11 } buildFeatures { compose = true } } } 93
91. Setting up the KMP plugin kotlin { android { namespace = "com.example.mylibrary" compileSdk = 36 minSdk = 24 compileOptions { sourceCompatibility = VERSION_11 targetCompatibility = VERSION_11 } buildFeatures { compose = true } } } 94
92. Setting up the KMP plugin kotlin { android { namespace = "com.example.mylibrary" compileSdk = 36 minSdk = 24 compilerOptions { jvmTarget = JvmTarget.JVM_11 } buildFeatures { compose = true } } } 95
93. Setting up the KMP plugin kotlin { android { namespace = "com.example.mylibrary" compileSdk = 36 minSdk = 24 compilerOptions { jvmTarget = JvmTarget.JVM_11 } } } 96
94. Setting up the KMP plugin dependencies { implementation(libs.androidx.preference) implementation(libs.kotlinx.datetime) implementation(libs.ktor.client.core) implementation(libs.ktor.client.content.negotiation) } 97
95. Setting up the KMP plugin dependencies { implementation(libs.androidx.preference) } kotlin { sourceSets { androidMain.dependencies { } commonMain.dependencies { } } } implementation(libs.kotlinx.datetime) implementation(libs.ktor.client.core) implementation(libs.ktor.client.content.negotiation) 98
96. Setting up the KMP plugin dependencies { implementation(libs.androidx.preference) } kotlin { sourceSets { androidMain.dependencies { } commonMain.dependencies { } } } implementation(libs.kotlinx.datetime) implementation(libs.ktor.client.core) implementation(libs.ktor.client.content.negotiation) 99
97. Setting up the KMP plugin kotlin { sourceSets { androidMain.dependencies { implementation(libs.androidx.preference) } commonMain.dependencies { } } } implementation(libs.kotlinx.datetime) implementation(libs.ktor.client.core) implementation(libs.ktor.client.content.negotiation) 100
98. Setting up the KMP plugin 101
99. Add AGP 9 opt-ins kotlin { android { androidResources.enable = true withHostTest { isIncludeAndroidResources = true } withDeviceTest { instrumentationRunner = "androidx.test.runner.AndroidJUnit } } } 102
100. Setting up the CMP plugin plugins { alias(libs.plugins.kotlin.multiplatform) alias(libs.plugins.android.multiplatform.library) alias(libs.plugins.compose.multiplatform) alias(libs.plugins.kotlin.compose) } + 104
101. Setting up the CMP plugin - + + androidx-compose-foundation = { module = "androidx.compose.foundation:foundation" module = "org.jetbrains.compose.foundation:foundation", version.ref = "composeMultiplatform" } 105
102. Setting up the CMP plugin 106
103. Setting up previews kotlin { sourceSets { commonMain.dependencies { implementation(libs.compose.ui.tooling.preview) } } } dependencies { androidRuntimeClasspath(libs.compose.ui.tooling) } 107
104. Setting up previews import androidx.compose.ui.tooling.preview.Preview import androidx.compose.ui.tooling.preview.PreviewLightDark @Preview(showBackground = true, fontScale = 2f) @PreviewLightDark @Composable fun ButtonPreview() { Button("Click me!") } 108
105. Migrate to CMP resources 109 kotlin { android { androidResources.enable = true } sourceSets { commonMain.dependencies { implementation(libs.compose.components.resources) } } } // Optional customization compose.resources { nameOfResClass = "Res" packageOfResClass = "org.example.resources" }
106. Migrate to CMP resources 110
107. Add more platforms kotlin { android { ...} iosArm64() iosSimulatorArm64() jvm() wasmJs { browser() } js { browser() } } 112
108. Add more platforms kotlin { android { ...} iosArm64() iosSimulatorArm64() jvm() wasmJs { browser() } js { browser() } } 113
109. Add more platforms kotlin { android { ...} iosArm64() iosSimulatorArm64() jvm() wasmJs { browser() } js { browser() } } 114
110. Umbrella module 115
111. Umbrella module 116
112. Umbrella module 117
113. Umbrella module 118
114. Umbrella module 119
115. Umbrella module 120
116. Umbrella module listOf( iosArm64(), iosSimulatorArm64(), ).forEach { iosTarget -> iosTarget.binaries.framework { baseName = "Shared" isStatic = true } } 121
117. Umbrella module 122
118. Umbrella module 123
119. Umbrella module 124
120. Umbrella module 125 Monorepo
121. Umbrella module 126 iOS repo Android repo
122. Umbrella module 127 iOS repo Android repo KMP repo
123. Umbrella module 128 iOS repo Android repo KMP repo
124. What’s next? kotl.in/kmp-team-intro • Project configurations • Introducing your team to KMP • Try Swift Export • Compose Hot Reload kotl.in/swift-export kotl.in/kmp-project-config kotl.in/compose-hot-reload 129
125. zsmb.co/talks Márton Braun @zsmb.co Going Multiplatform with Your Android App kotl.in/go-kmp-talk