[POC] Kotlin Multiplatform

This repository contains a proof-of-concept project which demonstrates the usage of the Kotlin MPP
feature using Kotlin JVM and Kotlin Native for sharing code between the Android and iOS platforms.

Requirements

• Android Studio >= 3.2.1
• Gradle 4.7
• Kotlin 1.3.20
• Xcode >= 10.0

IntelliJ is not required since Android Studio provides almost the same features and gives you the Android plugin
out of the box.

Project

This project contains three main folders:

• shared is the directory which contains the sources for the Kotlin MPP shared code;
• app contains the Android application which imports the shared module as Gradle dependency;
• ios-app contains the Xcode project for the iOS application. Open this folder with Xcode only.

The shared module

The shared module contains the three main source sets that compose a Kotlin MPP.

• commonMain is the directory which contains the shared code. Here goes the pure Kotlin code, which needs to
  be compiled both against JVM and Native;
• androidMain is the directory which contains the Android framework related code. Here you can access to the
  framework classes together with the Java ones. This source set will compile only against JVM;
• iOSMain is the directory which contains the iOS specific code. With the iOS Gradle plugin you can write
  framework-related stuff using Kotlin! Forget the buggy Xcode... for a while. This source set will compile only
  against the Kotlin Native compiler.

The build.gradle file of this module implements the kotlin-multiplatform plugin using:

apply plugin: 'kotlin-multiplatform'  

Since we need to use Android related classes in the androidMain source set, we need to implement also an Android Gradle plugin, as specified into the documentation.
We implemented the library plugin:

apply plugin: 'com.android.library'  

By implementing an Android plugin, the project is supposed to have a main source directory containing the canonical
AndroidManifest.xml. The only requirement you have is that the file contains a valid package name. Something as simple as:

<?xml version="1.0" encoding="utf-8"?>  
<manifest package="com.molo17.damianogiusti.kotlinnativepoc.shared"/>  

The Android plugin allows the kotlin-multiplatform plugin to make the presets.android extension available,
allowing us to apply it when defining source targets in the build.gradle
of the shared module.

The iOS app

The iOS app is contained into the ios-app/Kotlin-MPP folder. You can build it by your own by just opening it
using Xcode.

A build phase has been added to the project for invoking a script on every build. You can find the script into the
project directory. The script basically invokes the Gradle task which compiles the Kotlin code into a Xcode framework,
outputting a file named main.framework in the ios-app/Kotlin-MPP/kotlin-outputs directory, generated at the
first build.

The "Framework Search Paths" has been set to point to the script's output directory, and the built framework has been
added manually into the project, with the "Copy if needed" flag set to false.

Author

Damiano Giusti ([email protected])

External References

• https://kotlinlang.org/docs/reference/building-mpp-with-gradle.html
• https://kotlinlang.org/docs/tutorials/native/mpp-ios-android.html