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
   

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2. KotlinMultiplatform
   for Android Development
   

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3. 🤔
   https://dropbox.tech/mobile/the-not-so-hidden-cost-of-sharing-code-between-ios-and-android
   

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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.”
   

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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
   

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6. Kotlin Multiplatform?
   When Will You Use
   

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7. If/when it happens, it’ll be ORGANIC 🌱
   ¯\_(ツ)_/¯
   

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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
   

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9. What’s the Cost?
   

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10. Small Investment, Low Risk, …
    

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11. The Ultimate Source Set for Kotlin Multiplatform (KMP)
    commonMain
    

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14. commonMain
    

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15. JVM
    main Kotlin Compiler
    org.jetbrains.kotlin.android Plugin
    

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16. JVM
    main Kotlin Compiler
    org.jetbrains.kotlin.jvm Plugin
    

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17. JVM
    commonMain Kotlin Compiler
    org.jetbrains.kotlin.multiplatform Plugin
    

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18. JVM
    commonMain Kotlin Compiler
    org.jetbrains.kotlin.multiplatform Plugin
    JS
    iOS
    

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19. Plugins
    Kotlin + Gradle
    

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20. Kotlin + Gradle
    • kotlin(“android“)
    • kotlin(“jvm“)
    
    
    • kotlin(“multiplatform“)
    Plugins
    main
    main
    commonMain
    

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21. main and test
    Kotlin + Gradle
    dependencies {
    api(project(“:sample:module1”))
    implementation(project(“:sample:module2"))
    testImplementation(libs.kotlin.test.common)
    }
    

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22. main and test
    Kotlin + Gradle
    dependencies {
    api(project(“:sample:module1”))
    implementation(project(“:sample:module2"))
    testImplementation(libs.kotlin.test.common)
    }
    

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23. main and test
    Kotlin + Gradle
    dependencies {
    api(project(“:sample:module1”))
    implementation(project(“:sample:module2"))
    testImplementation(libs.kotlin.test.common)
    }
    

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24. main and test
    Kotlin + Gradle
    dependencies {
    api(project(“:sample:module1”))
    implementation(project(“:sample:module2"))
    testImplementation(libs.kotlin.test.common)
    }
    

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25. main and test
    Kotlin + Gradle
    dependencies {
    api(project(“:sample:module1”))
    implementation(project(“:sample:module2"))
    testImplementation(libs.kotlin.test.common)
    }
    

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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)
    }
    }
    }
    }
    

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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)
    }
    }
    }
    }
    

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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)
    }
    }
    }
    }
    

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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)
    }
    }
    }
    }
    

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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)
    }
    }
    }
    }
    

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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)
    }
    }
    }
    }
    

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32. Run Anywhere*
    Write Once
    * Yes, but…
    

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33. Multiplatform is Still Under Development
    https://blog.jetbrains.com/kotlin/2022/05/kotlin-multiplatform-mobile-beta-roadmap-update/
    

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34. Compiling Multiplatform Can Be Slow
    https://medium.com/yazio-engineering/speeding-up-kotlin-multiplatform-61ebf8dae560
    grade.properties
    

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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
    

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36. Multiplatform Plugin Adds Overhead
    7 Tasks 14 Tasks
    

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37. To Use Multiplatform with Zero Risk
    What Can We Do?
    

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38. Initial Proof of Concept
    https://github.com/handstandsam/ShoppingApp/pull/42
    

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39. Doesn’t Quite Work in Android Studio
    https://issuetracker.google.com/issues/229628556
    

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41. kmp4free
    

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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)
    }
    

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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)
    }
    

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44. Enable/Disable with Property
    # gradle.properties
    kmp4free=true
    or
    ./gradlew … -Pkmp4free=true
    

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45. JVM Project Structure
    

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46. JVM Project Structure
    

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47. JVM Project Structure
    kmp4free=false
    

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48. JVM Project Structure
    kmp4free=true
    kmp4free=false
    

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49. JVM Project Structure
    kmp4free=true
    kmp4free=false
    

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50. JVM Project Structure
    kmp4free=true
    kmp4free=false
    

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51. Source Set and Con
    fi
    guration Mapping
    How?
    

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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
    

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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
    

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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
    

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55. Migrating to commonMain
    com.android.library
    kotlin(“jvm”)
    kotlin(“multiplatform”)
    

    commonMain
    

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56. Migrating tests from androidTest ➡ jvm
    androidTest (instrumented)
    test (jvm)
    • Does not require any devices
    
    • Faster (usually)
    

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57. Demo!
    

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58. KMP4FREE 🆓
    is a low risk way
    to explore Kotlin Multiplatform
    

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59. No.
    Is it REALLY 🆓?
    

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60. Test and Experiment ♻
    • Create a multiplatform app that exercises it.
    

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61. Thank You
    Dropbox is Hiring!
    

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