Going Multiplatform with Your Android App (next app dev con Berlin 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. @ next.app devcon Wednesday, 10:20 Swift Export: Where We Stand Wednesday, 12:00 Going Multiplatform with Your Android App Wednesday, 14:50 Kotlin by JetBrains (roundtable) Thursday, 10:20 What’s New in Compose Multiplatform Friday, 12:00 Building a Multiplatform Window Manager for Fun 2
3. Friday, 12:00 The entire time Building a Multiplatform @ next.app devcon Window Manager for Fun Booth! 3
4. Why go KMP? One shared codebase More platforms Safe, low-risk Reuse Android skills Easier than you think! 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. What we’re doing today Strategy Modernizing Preparing for Multiplatform Going Multiplatform 9
10. Strategy
11. Incremental migration 11
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 Data 14
15. Bottom up UI UI Presentation Presentation Business logic Business logic Data 15
16. Bottom up UI UI Presentation Presentation Business logic Data 16
17. Bottom up UI UI Presentation Business logic Data 17
18. Bottom up UI Presentation Business logic Data 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 28
29. Quick start • Ship almost immediately 29
30. Quick start • Ship almost immediately • Nontrivial moves 30
31. Quick start • Ship almost immediately • Nontrivial moves • Fragmentation Ktor Coroutines Coil Koin KSP Retrofit RxJava Glide Dagger kapt 31
32. Quick start • Ship almost immediately • Nontrivial moves • Fragmentation • Structural changes ? 32
33. In-place migration 33
34. In-place migration Complete scope 34
35. In-place migration Initial scope Complete scope 35
36. In-place migration 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. Doing the work 0% 100% 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. Axes of migration Steps Modules Initial scope Complete scope 50
51. On pacing yourself 51
52. One step at a time Steps 52
53. Modernizing
54. Migrate from Java to Kotlin • Docs on kotlinlang.org kotl.in/java - to - kotlin • J2K converter in IntelliJ IDEA • AI tools kotl.in/agent - skills 54
55. Groovy to Kotlin DSL 56
56. kapt to KSP 57
57. kapt to KSP 59
58. 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") } 60
59. Update ALL the dependencies • Gradle • Android Gradle Plugin • Kotlin • Jetpack Compose kotl.in/kmp - compat kotl.in/cmp - compat kotl.in/gradle/agp9 • ... 61
60. Adopt coroutines kotl.in/coroutines - docs 62
61. Coroutine interop libraries github.com/Kotlin/kotlinx.coroutines/tree/master/reactive 63
62. Views to Jetpack Compose 64
63. Views to Jetpack Compose 65
64. Preparing for Multiplatform 66
65. Moving to multiplatform APIs commonMain androidMain iosMain jvmMain webMain 67
66. 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 68
67. 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 69
68. Find KMP libraries Klibs.io 70
69. Err on the side of multiplatform. 71
70. Handling the rest kotl.in/platform - apis 72
71. Handling the rest commonMain androidMain iosMain 73
72. Handling the rest commonMain expect fun getPlatformId (): String androidMain actual fun getPlatformId (): String = ... iosMain actual fun getPlatformId (): String = ... 74
73. Handling the rest commonMain interface androidMain class AndroidPlatform iosMain class IosPlatform fun init Platform { ... } (platform: Platform) : Platform { ... } : Platform { ... } 75
74. Handling the rest commonMain androidMain iosMain interface fun init Platform { ... } (platform: Platform) class AndroidPlatform context: Context : ) Platform { ... } class IosPlatform ( : Platform { ... } 76
75. Preparing for AGP 9 KMP requirements kotl.in/agp9 - blog 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 Variants / Native builds 81
80. Preparing for AGP 9 KMP requirements androidMain Variants / Native builds 82
81. Preparing for AGP 9 KMP requirements 83
82. Going Multiplatform
83. Setting up the KMP plugin 85
84. Setting up the KMP plugin 86
85. Setting up the KMP plugin (for Android) 87
86. Setting up the KMP plugin (for Android) Change plugins Move dependencies Move sources Add AGP 9 opt-ins 88
87. 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 89
88. Setting up the KMP plugin + + plugins { alias(libs.plugins.android.library) alias(libs.plugins.kotlin.multiplatform) alias(libs.plugins.android.multiplatform.library) } 90
89. 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 } } 91
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 } } } 92
91. 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 } } } 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 defaultConfig { 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 } } compileOptions { sourceCompatibility = VERSION_11 targetCompatibility = VERSION_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 } } } buildFeatures { compose = true } 97
96. Setting up the KMP plugin kotlin { android { namespace = "com.example.mylibrary" compileSdk = 36 minSdk = 24 } } compilerOptions { jvmTarget = JvmTarget.JVM_11 } 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) } 99
98. 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 { } } } 100
99. 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) } } } 101
100. 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) } } } 102
101. Setting up the KMP plugin 103
102. Add AGP 9 opt-ins kotlin { android { androidResources.enable = true } } withHostTest { isIncludeAndroidResources = true } withDeviceTest { instrumentationRunner = "androidx.test.runner.AndroidJUnit } 104
103. Add AGP 9 opt-ins kotlin { android { withJava() } } 105
104. 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) } 106
105. Setting up the CMP plugin + + androidx-compose-foundation = { module = "androidx.compose.foundation:foundation" module = "org.jetbrains.compose.foundation:foundation", version.ref = "composeMultiplatform" } 107
106. Setting up the CMP plugin 108
107. Setting up previews kotlin { sourceSets { commonMain.dependencies { implementation(libs.compose.ui.tooling.preview) } } } dependencies { androidRuntimeClasspath(libs.compose.ui.tooling) } 109
108. Setting up previews import import androidx.compose.ui.tooling.preview. androidx.compose.ui.tooling.preview. @Preview ( showBackground = true , fontScale @PreviewLightDark @Composable fun ButtonPreview () { Button ( "Click me!" ) } Preview PreviewLightDark = 2f ) 110
109. 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" } 111
110. Migrate to CMP resources 112
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. Add more platforms kotlin { android { ...} iosArm64() iosSimulatorArm64() jvm() } wasmJs { browser() } js { browser() } 116
114. Umbrella module 117
115. Umbrella module 118
116. Umbrella module 119
117. Umbrella module 120
118. Umbrella module 121
119. Umbrella module 122
120. Umbrella module listOf( iosArm64(), iosSimulatorArm64(), ).forEach { iosTarget -> iosTarget.binaries.framework { baseName = "Shared" isStatic = true } } 123
121. Umbrella module 124
122. Umbrella module 125
123. Umbrella module 126
124. Umbrella module Monorepo 127
125. Umbrella module iOS repo Android repo 128
126. Umbrella module iOS repo KMP repo Android repo 129
127. Umbrella module iOS repo KMP repo Android repo 130
128. What’s next? • Project configurations kotl.in/kmp - project - config • Introducing your team to KMP • Try Swift Export • Compose Hot Reload kotl.in/kmp - team - intro kotl.in/swift - export kotl.in/compose - hot - reload 131
129. jb.gg/android - to - kmp 132
130. @ next.app devcon Wednesday, 14:50 Kotlin by JetBrains (roundtable) Thursday, 10:20 What’s New in Compose Multiplatform Friday, 12:00 Building a Multiplatform Window Manager for Fun The entire time Booth! 133
131. Friday, 12:00 The entire time Building a Multiplatform @ next.app devcon Window Manager for Fun Booth! 134
132. Going Multiplatform with Your Android App kotl.in/go - kmp - talk Márton Braun @zsmb.co zsmb.co/talks zsmb.co/talks