12- If you want to support older devices, consider iosArm32 too; Which you can find supported devices with their OS here:

Image by isupportmatrix

13- For now, I’m gonna put versions into gradle.properties in the root of the project. Later, I’ll separate modules with their own build.gradle files.

14- We’re gonna create a temporary function to just have a sample app for now and run it on iOS and Android. So, create shared/src/commonMain/kotlin/common.kt.

15- Create shared/src/androidMain/kotlin/common.kt and shared/src/iosMain/kotlin/common.ktaand create platfrom method with actual keyword and your desired method body.

16- Note: in android module’s build.gradle.kts you can use plugins { id("kotlin-multiplatfrom") or plugins { id("kotlin-android"). In case of the first choice, you’d need to put dependencies scope into kotlin { sourceSets {scope and add android() as well.

But apart from this, in the case of choosing the first option, you’d have more than one “multiplatform” plugin which might be a cause for possible issues.

17- Use HelloWorldMessage() in the Android module and run the Android app:

15- Create an iOS project: Create a new Xcode project -> iOS target -> Single View App and then fill the form and choose the root of the previous project. Remember to choose Storyboard for the user interface, instead of SwiftUI.

16- Note: Check gradle-wrapper.properties and sure Gradle version is more than 4.7 (which I suggest to set it on class six (6.X.X)). Why? Run ./gradlew --version on different gradle versions.

In this case, using val kotlinVersion: String by extra doesn’t work in settings.gradle.kts. So, we need to set the Kotlin version using requested.version which use the version of the plugin if one was specified, otherwise null. So:

17- Run packForXcode task to setup iOS Framework in the Xcode project model easily, whether with right Gradle panel in AS, Android Studio terminal, or Mac terminal.

You probably(👉 I didn’t get this error after I update Xcode, Android Studio and Kotlin version 👈) get this warning:

Which addressed here, here, etc.

18- Now, we need to add the shared framework to the Xcode project to be able to use common resources on iOS as well.

Go to Xcode, double click on the root of the project name(the blue icon: ios) to open target settings.

Under General tab, Under Frameworks, Libraries, and Embedded Content, press + -> Add Other… -> Add Files… -> address shared/build/xcode-frameworks/shared.framework folder.

19- Now we need to tell to the Xcode where to look for the framework.

Under the Build Settings tab, search for “Framework Search Paths”. Now add this relative path to both Debug and Release: “$(SRCROOT)/../shared/build/xcode-frameworks”.

20- Now we need to tell to the Xcode build our shared framework before each run.

Under the Build Phases -> + -> New Run Script Phase -> paste this snippet code in Shell content:

And drag this task on top of the other tasks.

21- Use HelloWorldMessage() in the ViewController.swift.

Now run the iOS app:

allprojects {
    repositories {
        mavenCentral()
        ...
        maven("https://dl.bintray.com/badoo/maven")google()
        jcenter()
    }
}

val reactiveVersion: String by extra...sourceSets {
        val commonMain by getting {
            dependencies {
                ...
                implementation("com.badoo.reaktive:reaktive:$reactiveVersion")
            }
        }
        ...
    }}

27- Remember if you tried the newer unstable Kotlin version, then regretted and set it back to a stable version(1.3.X), be sure that you uninstall Kotlin Plugin(with unstable version) and restart the IDE(to get the stable version automatically). Otherwise, you get this error:

28- Note: If you use kotlin() instead of id(), you must change dash(-) with a dot(.) and remove kotlin keyword if it exists. For example:

29- Objective-C supports “lightweight generics” defined on classes, with a relatively limited feature set. Swift can import generics defined on classes to help provide additional type information to the compiler.

Generic feature support for Objc and Swift differ from Kotlin, so the translation will inevitably lose some information, but the features supported retain meaningful information.

Generics are currently not enabled by default. To have the framework header written with generics, add an experimental flag to the compiler config:

iOSTarget("ios") {
    binaries {
        framework {
            baseName = "shared"
            freeCompilerArgs += "-Xobjc-generics"
        }
    }
}

For Kotlin/Native interoperability with Swift/Objective-C, check out here.

30- To have the logging feature in Ktor, check out this.

31- [Out of Date-Check #44]For determining build type in the shared module, there are a few tricks and libraries but, I preferred to pass the value(API_KEY) from android module to the shared module.

A minor advantage of this solution is, we avoid rebuilding the shared module when the API URL and token get changed.[Out of Date-Check #44]

32- Note: For the architecture, it’s not 100% MVVM that all we know; Cause we have to take care of our object lifecycle by ourselves. There is moko-mvvm but, I didn’t want to rely on a third-party component for the architecture. Maybe later when I try to improve the architecture(as I mentioned on ‘under development’ section), I realize that that component is the best solution so far.

33- If you use opt-in requirements for features in the experimental state, carefully handle the API graduation to avoid breaking the client code.

To use experimental opt-in annotation, we need to add -Xopt-in=kotlin.RequiresOptIn to the compiler argument. I’ve passed as the second parameter to sections where we defined jvmTarget = “1.8” but, didn’t work for me. So, I’ve used it like below in the shared’s build.gradle, inside sourceSet scope:

implementation 'com.badoo.reaktive:coroutines-interop:<latest-version>'

For more information, please take a look into this.

Update 08/2020:

44- After using Kodein as a DI/Service Locator library, I’m setting API_KEY in shared module -> DI class. A benefit of this, we’d not set this key multiple times in different platforms.

A few points we need to take into account:

• We have to set jvmTarget to 1.8 in android and shared modules.
• We use kotlin.native.concurrent.ThreadLocal on the DI class to prevent “Unexpected mutability issue” on Koltin-Native.
• Changes to apply Kodein.

45- Done!

Result 📺

Tags: Android,iOS,Kotlin Multiplatform,Rxjava,Kotlin

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Originally published: July 27, 2020