Going Multiplatform with Your Android App (mDevCamp 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.

https://zsmb.co/talks/going-multiplatform-with-your-android-app/

Transcript

1. Going Multiplatform with Your Android App Márton Braun Developer Advocate
2. Platform Platform Platform
3. Going Multiplatform with Your Android App Márton Braun Developer Advocate
4. What we’re doing today Strategy Modernizing Preparing for Multiplatform Going Multiplatform 4
5. What we’re doing today Strategy Modernizing Preparing for Multiplatform Going Multiplatform 5
6. What we’re doing today Strategy Modernizing Preparing for Multiplatform Going Multiplatform 6
7. What we’re doing today Strategy Modernizing Preparing for Multiplatform Going Multiplatform 7
8. What we’re doing today Strategy Modernizing Preparing for Multiplatform Going Multiplatform 8
9. Strategy
10. Incremental migration 10
12. Bottom up UI UI Presentation Presentation Business logic Business logic Data Data 12
13. Bottom up UI UI Presentation Presentation Business logic Business logic Data Data 13
14. Bottom up UI UI Presentation Presentation Business logic Business logic Data 14
15. Bottom up UI UI Presentation Presentation Business logic Data 15
16. Bottom up UI UI Presentation Business logic Data 16
17. Bottom up UI Presentation Business logic Data 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 26
27. Quick start 27
28. Quick start • Ship almost immediately 28
29. Quick start • Ship almost immediately • Nontrivial moves 29
30. Quick start • Ship almost immediately • Nontrivial moves • Fragmentation Ktor Coroutines Coil Koin KSP Retrofit RxJava Glide Dagger kapt 30
31. Quick start • Ship almost immediately • Nontrivial moves • Fragmentation • Structural changes ? 31
32. In-place migration 32
33. In-place migration Complete scope 33
34. In-place migration Initial scope Complete scope 34
35. In-place migration Initial scope Complete scope 35
36. Doing the work 0% 100% Initial scope Complete scope 36
37. Doing the work 0% 100% Initial scope Complete scope 37
38. Doing the work 0% 100% Initial scope Complete scope 38
39. Doing the work 0% 100% Initial scope Complete scope 39
40. Doing the work 0% 100% Initial scope Complete scope 40
41. Doing the work 0% 100% Initial scope Complete scope 41
42. Doing the work 0% 100% Initial scope Complete scope 42
43. Axes of migration 🪓 Steps Modules Initial scope Complete scope 43
44. Axes of migration 🪓 Steps Modules Initial scope Complete scope 44
45. Axes of migration 🪓 Steps Modules Initial scope Complete scope 45
46. Axes of migration 🪓 Steps Modules Initial scope Complete scope 46
47. Axes of migration 🪓 Steps Modules Initial scope Complete scope 47
48. Axes of migration 🪓 Steps Modules Initial scope Complete scope 48
49. Axes of migration 🪓 Steps Modules Initial scope Complete scope 49
50. On pacing yourself 50
51. One step at a time Steps 51
52. Modernizing
53. Migrate from Java to Kotlin • Docs on kotlinlang.org kotl.in/java-to-kotlin • J2K converter in Intell" IDEA • AI tools kotl.in/agent-skills 53
54. Groovy to Kotlin DSL 55
55. kapt to KSP 56
56. kapt to KSP 58
57. 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") } 59
58. Update ALL the dependencies • Gradle • Android Gradle Plugin • Kotlin • Jetpack Compose kotl.in/kmp-compat kotl.in/cmp-compat kotl.in/gradle/agp9 •… 60
59. Adopt coroutines kotl.in/coroutines-docs 61
60. Coroutine interop libraries github.com/Kotlin/kotlinx.coroutines/tree/master/reactive 62
61. Views to Jetpack Compose 63
62. Views to Jetpack Compose 64
63. Preparing for Multiplatform 65
64. Moving to multiplatform APIs commonMain androidMain iosMain jvmMain webMain 66
65. A few common replacements JDK, Android APIs Kotlin standard library java.time kotlinx-datetime JUnit kotlin.test, kotest Moshi, Jackson, Gson kotlinx.serialization OkHttp Ktor Retrofit Ktorfit gRPC kotlinx-rpc (Preview) SQLite SQLDelight Dagger, Anvil Metro Glide Coil 67
66. Already good to go Kotlin standard library kotlinx-datetime Compose kotlin.test, kotest Koin kotlinx.serialization Arrow Ktor Room Ktorfit DataStore kotlinx-rpc (Preview) Apollo GraphQL SQLDelight Metro Coil 68
67. Find KMP libraries Klibs.io 69
68. Err on the side of multiplatform. 70
69. Handling the rest kotl.in/platform-apis 71
70. Handling the rest commonMain expect fun getPlatform androidMain actual fun getPlatform iosMain actual fun getPlatform 72
71. Handling the rest commonMain expect fun getPlatformId(): String androidMain actual fun getPlatformId(): String = !!... iosMain actual fun getPlatformId(): String = !!... 73
72. Handling the rest commonMain androidMain iosMain interface Platform { !!... } fun init(platform: Platform) class AndroidPlatform : Platform { !!... } class IosPlatform : Platform { !!... } 74
73. Handling the rest commonMain androidMain iosMain interface Platform { !!... } fun init(platform: Platform) class AndroidPlatform( context: Context ) : Platform { !!... } class IosPlatform : Platform { !!... } 75
74. Preparing for AGP 9 KMP requirements kotl.in/agp9-blog 76
75. Preparing for AGP 9 KMP requirements Variants / Native builds 77
76. Preparing for AGP 9 KMP requirements Variants / Native builds 78
77. Preparing for AGP 9 KMP requirements Variants / Native builds 79
78. Preparing for AGP 9 KMP requirements Variants / Native builds 80
79. Preparing for AGP 9 KMP requirements androidMain Variants / Native builds 81
80. Preparing for AGP 9 KMP requirements 82
81. Going Multiplatform
82. Setting up the KMP plugin 84
83. Setting up the KMP plugin 85
84. Setting up the KMP plugin (for Android) 86
85. Setting up the KMP plugin (for Android) Change plugins Move dependencies Move sources Add AGP 9 opt-ins 87
86. Setting up the KMP plugin (for Android) Change plugins Move dependencies Move sources Add AGP 9 opt-ins Set up Compose Multiplatform Configure previews Use multiplatform resources 88
87. Setting up the KMP plugin + + plugins { alias(libs.plugins.android.library) alias(libs.plugins.kotlin.multiplatform) alias(libs.plugins.android.multiplatform.library) } 89
88. 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 } } 90
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 } } } 91
90. 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 } } } 92
91. 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
92. 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 } } } 94
93. 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 } 95
94. Setting up the KMP plugin kotlin { android { namespace = "com.example.mylibrary" compileSdk = 36 minSdk = 24 compilerOptions { jvmTarget = JvmTarget.JVM_11 } } } buildFeatures { compose = true } 96
95. Setting up the KMP plugin kotlin { android { namespace = "com.example.mylibrary" compileSdk = 36 minSdk = 24 } } compilerOptions { jvmTarget = JvmTarget.JVM_11 } 97
96. 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) } 98
97. 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) } kotlin { sourceSets { androidMain.dependencies { } commonMain.dependencies { } } } 99
98. 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) } } } 100
99. 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) } } } 101
100. Setting up the KMP plugin 102
101. Add AGP 9 opt-ins kotlin { android { androidResources.enable = true } } withHostTest { isIncludeAndroidResources = true } withDeviceTest { instrumentationRunner = "androidx.test.runner.AndroidJUnit } 103
102. Add AGP 9 opt-ins kotlin { android { withJava() } } 104
103. 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) } 105
104. Setting up the CMP plugin + + androidx-compose-foundation = { module = "androidx.compose.foundation:foundation" module = "org.jetbrains.compose.foundation:foundation", version.ref = "composeMultiplatform" } 106
105. Setting up the CMP plugin 107
106. Setting up previews kotlin { sourceSets { commonMain.dependencies { implementation(libs.compose.ui.tooling.preview) } } } dependencies { androidRuntimeClasspath(libs.compose.ui.tooling) } 108
107. 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!") } 109
108. Migrate to CMP resources kotlin { android { androidResources.enable = true } sourceSets { commonMain.dependencies { implementation(libs.compose.components.resources) } } } // Optional customization compose.resources { nameOfResClass = "Res" packageOfResClass = "org.example.resources" } 110
109. Migrate to CMP resources 111
110. Add more platforms kotlin { android { ...} iosArm64() iosSimulatorArm64() jvm() } wasmJs { browser() } js { browser() } 113
111. Add more platforms kotlin { android { ...} iosArm64() iosSimulatorArm64() jvm() } wasmJs { browser() } js { browser() } 114
112. Add more platforms kotlin { android { ...} iosArm64() iosSimulatorArm64() jvm() } wasmJs { browser() } js { browser() } 115
113. Umbrella module 116
114. Umbrella module 117
115. Umbrella module 118
116. Umbrella module 119
117. Umbrella module 120
118. Umbrella module 121
119. Umbrella module listOf( iosArm64(), iosSimulatorArm64(), ).forEach { iosTarget -> iosTarget.binaries.framework { baseName = "Shared" isStatic = true } } 122
120. Umbrella module 123
121. Umbrella module 124
122. Umbrella module 125
123. Umbrella module Monorepo 126
124. Umbrella module iOS repo Android repo 127
125. Umbrella module iOS repo KMP repo Android repo 128
126. Umbrella module iOS repo KMP repo Android repo 129
127. What’s next? • Project configurations kotl.in/kmp-project-config • Introducing your team to KMP • Try Swift Export kotl.in/kmp-team-intro kotl.in/swift-export • Compose Hot Reload kotl.in/compose-hot-reload 130
128. jb.gg/android-to-kmp 131
129. Going Multiplatform with Your Android App kotl.in/go-kmp-talk Márton Braun @zsmb.co zsmb.co/talks