What is Kotlin Multiplatform? In short, it’s the future of mobile development. You don’t believe me? Let me try to persuade you: Kotlin Multiplatform is still young, but it’s a very promising technology. It allows developers to share parts of code between different platforms, whether it’s your backend, or an iOS app, or an Android app, or even a web or desktop. Kotlin will find its way anywhere.

It’s particularly great for mobile developers, because it can help us leverage the best of Kotlin to quickly build apps that look amazing both on iOS and Android. You’ll be able to share lots of code between the two platforms and focus on making UI appealing to the user! Moreover, you can build a backend in Kotlin that will complement your KMM app and make it even more sustainable.

I’ve spent a lot of time researching on KMP, struggling through gradle files and dependencies, building apps for work and for myself and would love to share my experience with everyone else who’s interested.

So stock up with pizza ingredients and let’s explore the exciting world of KMP together! 🤓

This repository will accompany each step of the blog: KMPizza Repo

What do we need to serve our pizza?

Right! A backend.

And you know what, we can do that with Kotlin. So let’s start.

Add another module to our basic setup: backend. Click on the project and choose New -> Module. Name it “backend”. Choose “No Activity” when asked to create one.

If you check out the project settings.gradle.kts, you will see that the backend module is included in the project now.

rootProject.name = "kmpizza"
include(":androidApp")
include(":shared")
include(":backend")

As our recipe collection is going to grow into a big project for multiple platforms, we’ll need to keep our dependencies clean and organised. To do so, we’ll setup buildSrc for dependency management. Add a new directory to the root folder and name it “buildSrc”.

In this module create Versions.kt and build.gradle.kts to match the following file structure:

In Versions.kt file you wil keep all the dependencies for different modules in this project.

Add the following to the build.gradle.kts file:

plugins {
   `kotlin-dsl`
}

repositories {
   gradlePluginPortal()
   maven("https://dl.bintray.com/kotlin/kotlinx/")
}

To make sure we haven’t broken anything yet, sync the project, choose androidApp configuration and run the app.

You’ll see a “Hello, Android!” on your device, which is an initial setup that comes with the KMM Application Android Studio Project.

If you want to try it in XCode, open iosApp.xcworkspace.

Then run it on a simulator and you’ll see a “Hello, iOS!” screen. Great, everything is still working 😉

Or is it? If you try running it on a real device you may get an error Signing for "iosApp" requires a development team. Select a development team in the Signing & Capabilities editor. Let’s quickly fix it. Select the project name in XCode and go to Signing&Capabilites in the project editor. There change your team to Personal Team, something like this:

Now you may see another error if you try running the app again: Command PhaseScriptExecution failed with a nonzero exit code 😱

No worries, we’ll fix it too. First, you need to sync the gradle project in Android Studio, then go to the iosApp directory in your terminal and run pod install there.

Now try running again. If you get a warning like this

Then go to Settings -> General -> Device Management and choose to trust your developer account.

Run the app again. Finally we see the greeting on a real device!

And just like this, one step at a time we’ll continue building our multiplatform app. 🍕

Everyone likes pizza, so let’s create a recipe app, where you can save all the yummy pizza recipes that you’ve tried and would like to recreate sometime in the future!

Our first step will be to create a Kotlin Multiplatform project.

1. Open Android studio, go to File -> New -> New Project and create a KMM Application.

2. Choose a name for the application and the package, define your save location and click Next.

3. In the following screen you’ll have to name your Android Application, iOS Application and shared Module. You don’t need to customize anything here, so just leave it as is and click Finish.

Now we’ve got a basic setup for our future KMM project. This way we can keep all our project related Kotlin code in the same place. As you can see, it has an androidApp, where you can work on your Android App just as you usually would. You also have an iosApp that holds your ios application, which you can work with in XCode. Moreover, you have a shared module now, which is divided into androidMain, commonMain and iosMain. CommonMain will be the source of all your shared logic within the app, and the other two will hold platform specific implementations for expect functions and classes.