Embracing commonMain for Android Development - Droidcon SF 2022

Video: https://www.droidcon.com/2022/06/28/embracing-commonmain-for-android-development/

We are all excited to use Kotlin Multiplatform, but on large projects it’s hard to figure out where to start using it without introducing risk. In this talk, I’ll give you techniques to start writing your code in commonMain right now. The code you write in commonMain is just Kotlin code, so it’s no different than what you write today, but with some slightly different configuration and guidelines that need to be followed. I’ll show you how to quickly set up your project configuration, and what guidelines to follow so you can start exercising your Multiplatform muscles. Writing code in commonMain helps promote modularity, and makes you think like a “Mobile developer” instead of just an “Android” developer.

Transcript

1. Sam Edwards - @HandstandSam Kotlin & Android GDE @ Dropbox Embracing commonMain 🫂 for Android Development Droidcon SF 2022
2. KotlinMultiplatform for Android Development
3. 🤔 https://dropbox.tech/mobile/the-not-so-hidden-cost-of-sharing-code-between-ios-and-android
4. “By writing code in a non-standard fashion, we took on overhead that we would have not had to worry about had we stayed with the widely used platform defaults. This overhead ended up being more expensive than just writing the code twice.”
5. The Overhead of: 1. Custom frameworks and libraries 2. Custom development environment 3. Addressing di ff erences between the platforms 4. Training, hiring, and retaining developers
6. Kotlin Multiplatform? When Will You Use
7. If/when it happens, it’ll be ORGANIC 🌱 ¯\_(ツ)_/¯
8. Plant a seed for Kotlin Multiplatform 🌱 and we’ll see where it takes us • Same Kotlin Code, di ff erent Gradle plugin • Forces modularity • Makes developers more likely to try coding in the other platform
9. What’s the Cost?
10. Small Investment, Low Risk, …
11. The Ultimate Source Set for Kotlin Multiplatform (KMP) commonMain
14. commonMain
15. JVM main Kotlin Compiler org.jetbrains.kotlin.android Plugin
16. JVM main Kotlin Compiler org.jetbrains.kotlin.jvm Plugin
17. JVM commonMain Kotlin Compiler org.jetbrains.kotlin.multiplatform Plugin
18. JVM commonMain Kotlin Compiler org.jetbrains.kotlin.multiplatform Plugin JS iOS
19. Plugins Kotlin + Gradle
20. Kotlin + Gradle • kotlin(“android“) • kotlin(“jvm“) • kotlin(“multiplatform“) Plugins main main commonMain
21. main and test Kotlin + Gradle dependencies { api(project(“:sample:module1”)) implementation(project(“:sample:module2")) testImplementation(libs.kotlin.test.common) }
22. main and test Kotlin + Gradle dependencies { api(project(“:sample:module1”)) implementation(project(“:sample:module2")) testImplementation(libs.kotlin.test.common) }
23. main and test Kotlin + Gradle dependencies { api(project(“:sample:module1”)) implementation(project(“:sample:module2")) testImplementation(libs.kotlin.test.common) }
24. main and test Kotlin + Gradle dependencies { api(project(“:sample:module1”)) implementation(project(“:sample:module2")) testImplementation(libs.kotlin.test.common) }
25. main and test Kotlin + Gradle dependencies { api(project(“:sample:module1”)) implementation(project(“:sample:module2")) testImplementation(libs.kotlin.test.common) }
26. commonMain and commonTest Con fi gurations Kotlin + Gradle kotlin { jvm() sourceSets { maybeCreate("commonMain").apply { dependencies { implementation(libs.kotlin.coroutines) } } maybeCreate("commonTest").apply { dependencies { implementation(libs.kotlin.test.common) implementation(libs.kotlin.test.annotations.common) } } } }
27. commonMain and commonTest Con fi gurations Kotlin + Gradle kotlin { jvm() sourceSets { maybeCreate("commonMain").apply { dependencies { implementation(libs.kotlin.coroutines) } } maybeCreate("commonTest").apply { dependencies { implementation(libs.kotlin.test.common) implementation(libs.kotlin.test.annotations.common) } } } }
28. commonMain and commonTest Con fi gurations Kotlin + Gradle kotlin { jvm() sourceSets { maybeCreate("commonMain").apply { dependencies { implementation(libs.kotlin.coroutines) } } maybeCreate("commonTest").apply { dependencies { implementation(libs.kotlin.test.common) implementation(libs.kotlin.test.annotations.common) } } } }
29. commonMain and commonTest Con fi gurations Kotlin + Gradle kotlin { jvm() sourceSets { maybeCreate("commonMain").apply { dependencies { implementation(libs.kotlin.coroutines) } } maybeCreate("commonTest").apply { dependencies { implementation(libs.kotlin.test.common) implementation(libs.kotlin.test.annotations.common) } } } }
30. commonMain and commonTest Con fi gurations Kotlin + Gradle kotlin { jvm() sourceSets { maybeCreate("commonMain").apply { dependencies { implementation(libs.kotlin.coroutines) } } maybeCreate("commonTest").apply { dependencies { implementation(libs.kotlin.test.common) implementation(libs.kotlin.test.annotations.common) } } } }
31. commonMain and commonTest Con fi gurations Kotlin + Gradle kotlin { jvm() sourceSets { maybeCreate("commonMain").apply { dependencies { implementation(libs.kotlin.coroutines) } } maybeCreate("commonTest").apply { dependencies { implementation(libs.kotlin.test.common) implementation(libs.kotlin.test.annotations.common) } } } }
32. Run Anywhere* Write Once * Yes, but…
33. Multiplatform is Still Under Development https://blog.jetbrains.com/kotlin/2022/05/kotlin-multiplatform-mobile-beta-roadmap-update/
34. Compiling Multiplatform Can Be Slow https://medium.com/yazio-engineering/speeding-up-kotlin-multiplatform-61ebf8dae560 grade.properties
35. Multiplatform Doesn’t Support Con fi guration Caching (Yet) https://youtrack.jetbrains.com/issue/KT-49933/Support-Gradle-Con fi guration-caching-with-HMPP
36. Multiplatform Plugin Adds Overhead 7 Tasks 14 Tasks
37. To Use Multiplatform with Zero Risk What Can We Do?
38. Initial Proof of Concept https://github.com/handstandsam/ShoppingApp/pull/42
39. Doesn’t Quite Work in Android Studio https://issuetracker.google.com/issues/229628556
41. kmp4free
42. JVM Project Structure plugins { kotlin("jvm") } dependencies { implementation(libs.kotlin.stdlib) implementation(project(":samples:jvm_kmp4free")) testImplementation(libs.kotlin.test.common) testImplementation(libs.truth) }
43. JVM Project Structure plugins { id("com.handstandsam.kmp4free") } dependencies { implementation(libs.kotlin.stdlib) implementation(project(":samples:jvm_kmp4free")) testImplementation(libs.kotlin.test.common) testImplementation(libs.truth) }
44. Enable/Disable with Property # gradle.properties kmp4free=true or ./gradlew … -Pkmp4free=true
45. JVM Project Structure
46. JVM Project Structure
47. JVM Project Structure kmp4free=false
48. JVM Project Structure kmp4free=true kmp4free=false
49. JVM Project Structure kmp4free=true kmp4free=false
50. JVM Project Structure kmp4free=true kmp4free=false
51. Source Set and Con fi guration Mapping How?
52. Primary Goals of kmp4free • No Risk, Single Line Change to Enable Multiplatform • Support JVM & Multiplatform Con fi g • Allow Experimentation and Possible Migration to Multiplatform
53. kmp4free=true • SourceSet Mapping • src/main ➡ src/commonMain • src/test ➡ src/jvmTest • Con fi guration Mapping • implementation ➡ commonMainImplementation • testImplementation ➡ jvmTestImplementation • Task Aliasing • :module:test ➡ :module:jvmTest
54. kmp4free=false • SourceSet Mapping • src/commonMain ➡ src/main • src/jvmMain ➡ src/main • src/commonTest ➡ src/test • src/jvmTest ➡ src/test • Con fi guration Mapping • commonMainImplementation ➡ implementation • commonTestImplementation ➡ testImplementation • jvmTestImplementation ➡ testImplementation
55. Migrating to commonMain com.android.library kotlin(“jvm”) kotlin(“multiplatform”) 
 commonMain
56. Migrating tests from androidTest ➡ jvm androidTest (instrumented) test (jvm) • Does not require any devices • Faster (usually)
57. Demo!
58. KMP4FREE 🆓 is a low risk way to explore Kotlin Multiplatform
59. No. Is it REALLY 🆓?
60. Test and Experiment ♻ • Create a multiplatform app that exercises it.
61. Thank You Dropbox is Hiring!