Introducing Kotlin Multiplatform in an existing project - droidcon Berlin 2021

Marco Gomiero
droidcon Berlin
Introducing

Kotlin Multiplatform
in an existing project

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droidcon Berlin - @marcoGomier
Marco Gomiero
👨💻 Android Engineer @ TIER 🛴 🇩🇪 🇮🇹
 
Google Developer Expert for Kotlin
> Twitter: @marcoGomier
 
> Github: prof18
 
> Website: marcogomiero.com

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• Not about compiling all code for all platforms

• Share as much [NO UI] code as possible

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Common Kotlin
Kotlin/JVM Kotlin/JS Kotlin/Native
Java

Android
Browser

NodeJS
Android NDK

iOS

macOS

watchOS

tvOS

Linux

Windows

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Common Kotlin
Kotlin/JVM Kotlin/JS Kotlin/Native
Java

Android
Browser

NodeJS
Android NDK

iOS

macOS

watchOS

tvOS

Linux

Windows
Mobile App

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droidcon Berlin @marcoGomier
New Project

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New Projects: Android Studio plugin

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.

└── kmm-project

├── androidApp

├── iosApp

└── shared
Same Repository

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shared
androidApp
Gradle Module
Android

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//
settings.gradle.kts

include(":shared")

//
build.gradle.kts

implementation(project(":shared"))
Android

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shared
androidApp iosApp
Gradle Module Framework
iOS

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New Projects: Android Studio plugin

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embedAndSignAppleFrameworkForXcode
https://blog.jetbrains.com/kotlin/2021/07/multiplatform-gradle-plugin-improved-for-connecting-kmm-modules/
packForXcode
From Kotlin 1.5.20
iOS

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CocoaPods integration
https://kotlinlang.org/docs/reference/native/cocoapods.html
Pod
::
Spec.new do |spec|

spec.name = 'shared'

spec.version = '1.0-SNAPSHOT'

spec.homepage = 'Link to a Kotlin/Native module homepage'

spec.source = { :git
=>
"Not Published", :tag
=
>
"Cocoapods/
#{
spec.name}
#{

spec.authors = ''

spec.license = ''

spec.summary = 'Some description for a Kotlin/Native module'

spec.static_framework = true

spec.vendored_frameworks = "build/cocoapods/framework/shared.framework"

spec.libraries = "c
++
"

spec.module_name = "
# {
spec.name}_umbrella"

spec.pod_target_xcconfig = {

'KOTLIN_TARGET[sdk=iphonesimulator*]'
=>
'ios_x64',

'KOTLIN_TARGET[sdk=iphoneos*]'
=>
'ios_arm',

'KOTLIN_TARGET[sdk=watchsimulator*]'
=>
'watchos_x86',

'KOTLIN_TARGET[sdk=watchos*]'
=>
'watchos_arm',

'KOTLIN_TARGET[sdk=appletvsimulator*]'
= >
'tvos_x64',

'KOTLIN_TARGET[sdk=appletvos*]'
=>
'tvos_arm64',

'KOTLIN_TARGET[sdk=macosx*]'
= >
'macos_x64'

}

spec.script_phases = [

{

:name
= >
'Build shared',

:execution_position
= >
:before_compile,

:shell_path
=>
'/bin/sh',

:script
=> < <-
SCRIPT

set -ev

REPO_ROOT="$PODS_TARGET_SRCROOT"

"$REPO_ROOT/
..
/gradlew" -p "$REPO_ROOT" :shared:syncFramework \

-Pkotlin.native.cocoapods.target=$KOTLIN_TARGET \

-Pkotlin.native.cocoapods.configuration=$CONFIGURATION \

-Pkotlin.native.cocoapods.cflags="$OTHER_CFLAGS" \

-Pkotlin.native.cocoapods.paths.headers="$HEADER_SEARCH_PATHS" \

-Pkotlin.native.cocoapods.paths.frameworks="$FRAMEWORK_SEARCH_PATHS"

SCRIPT

}

]

end

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iOS Project: Podfile
pod 'shared', :path
=>
'
..
/shared'

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Existing Project

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Photo by Ashkan Forouzani on Unsplash

🙅
shared
androidApp iosApp
Gradle
Module
Framework
Same Repository

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Photo by Erwan Hesry on Unsplash
You can choose a little
piece of tech stack to
start with

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• Boring code to write multiple times

• Code/feature that centralises the source of truth (i.e. a field
is nullable or not)

• Code/feature that can be gradually extracted
Where to start?

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• DTOs

• Common Models

• Utility methods, aka `object Utils {}`

• Analytics

•
. . .
Where to start?

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Existing Projects: Intellij Wizard

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Common Kotlin
Android App iOs App
.aar Framework
 
Maven
 
Cocoa Repo

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Common Kotlin
Android App iOs App
.aar Framework
 
Maven
 
Cocoa Repo
Android App Repository
KMP Repository
iOs App Repository

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How to publish: Android

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droidcon Berlin - @marcoGomier https://github.com/prof18/shared-hn-android-ios-backend
* based on a true story project

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plugins {

//..
.

id("maven-publish")

}

group = "com.prof18.hn.foundation"

version = "1.0"

publishing {

repositories {

maven{

credentials {

username = "username"

password = "pwd"

}

url = url("https:
//
mymavenrepo.it")

}

}

}

Setup a Maven repository to share the artifacts: build.gradle.kts

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Publish the artifacts
./gradlew publish

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Publish the artifacts
./gradlew publish

./gradlew publishToMavenLocal

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Android
implementation(“com.prof18.hn.foundation:hn-foundation-android:2.0.0")

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How to publish: iOS

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🥵

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embedAndSignAppleFrameworkForXcode
packForXcode
CocoaPods integration

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🤔

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XCFramework

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NEW
https://devstreaming-cdn.apple.com/videos/wwdc/2019/416h8485aty341c2/416/416_binary_frameworks_in_swift.pdf

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droidcon Berlin - @marcoGomier https://devstreaming-cdn.apple.com/videos/wwdc/2019/416h8485aty341c2/416/416_binary_frameworks_in_swift.pdf
NEW
iOS mac
OS
watch
OS
tvOS

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https:
//
developer.apple.com/videos/play/wwdc2019/416/

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XCFramework
Official Support from Kotlin 1.5.30
https://kotlinlang.org/docs/whatsnew1530.html#support-for-xcframeworks

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XCFramework prior to Kotlin 1.5.30
https://github.com/prof18/kmp-xcframework-sample/blob/pre-kotlin-1.5.30/build.gradle.kts#L86
register("buildReleaseXCFramework", Exec
::
class.java) {

description = "Create a Release XCFramework"

dependsOn("link${libName}ReleaseFrameworkIosArm64")

dependsOn("link${libName}ReleaseFrameworkIosX64")

val arm64FrameworkPath = "$rootDir/build/bin/iosArm64/${libName}ReleaseFramework/${libName}.framework"

val arm64DebugSymbolsPath =

"$rootDir/build/bin/iosArm64/${libName}ReleaseFramework/${libName}.framework.dSYM"

val x64FrameworkPath = "$rootDir/build/bin/iosX64/${libName}ReleaseFramework/${libName}.framework"

val x64DebugSymbolsPath = "$rootDir/build/bin/iosX64/${libName}ReleaseFramework/${libName}.framework.dSYM"

val xcFrameworkDest = File("$rootDir/
..
/kmp-xcframework-dest/$libName.xcframework")

executable = "xcodebuild"

args(mutableListOf().apply {

add("-create-xcframework")

add("-output")

add(xcFrameworkDest.path)

//
Real Device

add("-framework")

add(arm64FrameworkPath)

add("-debug-symbols")

add(arm64DebugSymbolsPath)

//
Simulator

add("-framework")

add(x64FrameworkPath)

add("-debug-symbols")

add(x64DebugSymbolsPath)

})

doFirst {

xcFrameworkDest.deleteRecursively()

}

}

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https:
/
/
www.marcogomiero.com/posts/2021/build-xcframework-kmp/

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XCFramework: build.gradle.kts
https://github.com/prof18/shared-hn-android-ios-backend/blob/main/hn-foundation/build.gradle.kts
import org.jetbrains.kotlin.gradle.plugin.mpp.apple.XCFramework

val libName = "LibraryName"

kotlin {

val xcFramework = XCFramework(libName)

ios {

binaries.framework(libName) {

xcFramework.add(this)

}

}

...

}

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assemble${libName}XCFramework

assemble${libName}DebugXCFramework

assemble${libName}ReleaseXCFramework
XCFramework: Gradle tasks

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.

├── build

├── XCFrameworks

├── debug

│ └── LibraryName.xcframework

└── release

└── LibraryName.xcframework

XCFramework

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droidcon Berlin - @marcoGomier https://github.com/prof18/hn-foundation-cocoa-xcframework
CocoaPod Repository

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HNFoundation.podspec

https://github.com/prof18/hn-foundation-cocoa-xcframework/blob/main/HNFoundation.podspec
Pod
::
Spec.new do |s|

# ――― Spec Metadata ―――――――――――――――――――――――――――――――――――――――――――――――――――――――――― #

#

# These will help people to find your library, and whilst it

# can feel like a chore to fill in it's definitely to your advantage. The

# summary should be tweet-length, and the description more in depth.

#

s.name = "HNFoundation"

s.version = "2.0.0"

s.summary = "HNFoundation KMP library"

s.homepage = "https:
//
github.com/prof18/hn-foundation-cocoa-xcframework"

s.license = "Apache"

s.author = { "Marco Gomiero"
= >
"[email protected]" }

s.vendored_frameworks = 'HNFoundation.xcframework'

s.source = { :git
=>
"[email protected]:prof18/hn-foundation-cocoa-xcframework", :tag
=>
"
#{
s.version}" }

s.exclude_files = "Classes/Exclude"

end

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https:
//
guides.cocoapods.org/making/private-cocoapods.html

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iOs Project: Podfile
# For develop releases:

pod 'HNFoundation', :git
=>
“[email protected]:prof18/hn-foundation-cocoa-xcframework.git", :branch
=
>
'develop'

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iOs Project: Podfile
# For develop releases:

=>
“[email protected]:prof18/hn-foundation-cocoa-xcframework.git", :branch
= >
'develop'

# For stable releases

=>
“[email protected]:prof18/hn-foundation-cocoa-xcframework.git", :tag
=>
‘2.0.0'

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register("publishDevFramework") {

description = "Publish iOs framework to the Cocoa Repo"

doFirst {

project.exec {

workingDir = File("$rootDir/
..
/
..
/hn-foundation-cocoa-xcframework")

commandLine("git", "checkout", "develop").standardOutput

}

}

dependsOn("assemble${libName}DebugXCFramework")

doLast {

copy {

from("$buildDir/XCFrameworks/debug")

into("$rootDir/
..
/
..

}

.. ..

https://github.com/prof18/shared-hn-android-ios-backend/blob/main/hn-foundation/build.gradle.kts#L110
Publish Dev Framework Task

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..
/
..

commandLine("git", "checkout", "develop").standardOutput

}

}

dependsOn("assemble${libName}DebugXCFramework")

doLast {

copy {

from("$buildDir/XCFrameworks/debug")

into("$rootDir/
..
/
..

}

val dir = File("$rootDir/
..
/
..
/hn-foundation-cocoa-xcframework/$libName.podspec")

val tempFile = File("$rootDir/
..
/
..
/hn-foundation-cocoa-xcframework/$libName.podspec.new")

val reader = dir.bufferedReader()

val writer = tempFile.bufferedWriter()

var currentLine: String?

while (reader.readLine().also { currLine
->
currentLine = currLine }
!=
null) {

if (currentLine
?.
startsWith("s.version")
==
true) {

writer.write("s.version = \"${libVersionName}\"" + System.lineSeparator())

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into("$rootDir/
..
/
..

}

..
/
..

..
/
..




->
!=
null) {

if (currentLine
?.
==
true) {

writer.write("s.version = \"${libVersionName}\"" + System.lineSeparator())

} else {

writer.write(currentLine + System.lineSeparator())

}

}

writer.close()

reader.close()

val successful = tempFile.renameTo(dir)

if (successful) {

project.exec {

..
/
..

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if (successful) {

project.exec {

..
/
..

commandLine("git", "add", ".").standardOutput

}

val dateFormatter = SimpleDateFormat("dd/MM/yyyy - HH:mm", Locale.getDefault())

project.exec {

..
/
..

commandLine(

"git",

"commit",

"-m",

"\"New dev release: ${libVersionName}-${dateFormatter.format(Date())}\""

).standardOutput

}

project.exec {

..
/
..

commandLine("git", "push", "origin", "develop").standardOutput

}

}

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https://github.com/prof18/shared-hn-android-ios-backend/blob/main/hn-foundation/build.gradle.kts#L177
Publish Release Framework Task
register("publishFramework") {

description = "Publish iOs framework to the Cocoa Repo"

doFirst {

project.exec {

..
/
..

commandLine("git", "checkout", "main").standardOutput

}

}

dependsOn("assemble${libName}ReleaseXCFramework")

doLast {

copy {

from("$buildDir/XCFrameworks/release")

into("$rootDir/
..
/
..

}

.. ..

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project.exec {

..
/
..

commandLine("git", "checkout", "main").standardOutput

}

}

dependsOn("assemble${libName}ReleaseXCFramework")

doLast {

copy {

from("$buildDir/XCFrameworks/release")

into("$rootDir/
..
/
..

}

..
/
..

..
/
..




->
!=
null) {

if (currentLine
?.
==
true) {

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project.exec {

..
/
..

commandLine("git", "add", ".").standardOutput

}

project.exec {

..
/
..

commandLine("git", "commit", "-m", "\"New release: ${libVersionName}\"").standardOu

}

project.exec {

..
/
..

commandLine("git", "tag", libVersionName).standardOutput

}

project.exec {

..
/
..

commandLine("git", "push", "origin", "main", "
--
tags").standardOutput

}

}

}

}

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🎉

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Concurrency

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• Kotlin/Native different from the JVM

• One thread
->
no problems, you can use mutable objects

• Many thread
-
>
only immutable objects
Concurrency
https://kotlinlang.org/docs/mobile/concurrency-overview.html

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Uncaught Kotlin exception: kotlin.native.IncorrectDereferenceException:
illegal attempt to access non-shared @c2ddb8 from other thread

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🥶 Freeze the object to share
it between threads

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override fun deserialize(jsonString: String): NewsDTO {

val newsDTO: NewsDTO = json.decodeFromString(jsonString)

newsDTO.freeze()

return newsDTO

}

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droidcon Berlin - @marcoGomier https://blog.jetbrains.com/kotlin/2021/08/try-the-new-kotlin-native-memory-manager-development-preview/

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Conclusions

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Faced [and resolved] difficulties
• How to organise the project without a monorepo

• How to effectively distribute the iOS framework

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Start little

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Start little
Go bigger
then

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Start little then go bigger
• Validate the process with “little” effort

• Then you can go bigger and share more “features”
 

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Bibliography / Useful Links
• https:
/ /
kotlinlang.org/lp/mobile/

• https:
/ /
www.marcogomiero.com/posts/2020/my-2cents-cross-platform/

• https:
/ /
giansegato.com/essays/a-technical-framework-for-early-stage-startups/

• https:
/ /
giansegato.com/essays/the-ebb-and-the-flow-of-product-development/

• https:
/ /
www.marcogomiero.com/posts/2021/build-xcframework-kmp/

• https:
/ /
www.marcogomiero.com/posts/2021/kmp-xcframework-official-support/

• https:
/ /
www.marcogomiero.com/posts/2020/kotlin-serialization-alamofire/

• https:
/ /
www.marcogomiero.com/posts/2021/kmp-existing-project/

• https:
/ /
www.youtube.com/watch?v=oxQ6e1VeH4M

• https:
/ /
dev.to/kpgalligan/series/3739

• https:
/ /
blog.jetbrains.com/kotlin/2021/08/try-the-new-kotlin-native-memory-manager-
development-preview/

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Marco Gomiero
droidcon Berlin
Thank you!

> Twitter: @marcoGomier
 
> Github: prof18
 
> Website: marcogomiero.com

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Introducing Kotlin Multiplatform in an existing project - droidcon Berlin 2021

Introducing Kotlin Multiplatform in an existing project - droidcon Berlin 2021

Marco Gomiero

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