KMP Project Setup and Structure

What is Kotlin Multiplatform?

Kotlin Multiplatform (KMP) lets you write business logic once in Kotlin and run it on Android, iOS, desktop, and more. You share the logic (networking, database, validation) and keep each platform's UI native.

The current stable version is Kotlin 2.4.x with the K2 compiler.

When to Use KMP

• You have an Android and an iOS app with duplicated logic.
• You want a shared data layer but native UIs.
• You want to publish a library for many platforms from one codebase.

Do not use KMP when you have only one target. A plain Kotlin/JVM project is simpler.

Create a Project with the Wizard

1. Open kpm.kotlinlang.org (the KMP wizard).
2. Name your project, for example MyApp.
3. Pick targets: Android, iOS (and more if you want).
4. Click Download and unzip the project.
5. Open it in Android Studio or IntelliJ IDEA.

Run the app on each target from the IDE run configurations.

Project Structure

A KMP project has a shared module with source sets for each platform.

Diagram: A KMP shared module with common code and platform-specific code. commonMain holds shared code; androidMain and iosMain hold platform code.

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• commonMain — code shared by all targets. No platform imports here.
• androidMain — Android-only code (uses android.* APIs).
• iosMain — iOS-only code (uses Apple frameworks via Kotlin/Native).

Build Configuration

The shared module's build.gradle.kts declares the targets and dependencies:

// shared/build.gradle.kts
kotlin {
    androidTarget()
    iosArm64()
    iosX64()
    iosSimulatorArm64()

    sourceSets {
        commonMain.dependencies {
            implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.10.2")
        }
    }
}

Add shared dependencies inside commonMain.dependencies. They work on every target.

Run It

The wizard generates a sample Greeting. Run the Android and iOS configurations. Both print the same shared message.

Greeting: Hello, KMP!

Practice Exercise

1. Create a KMP project with the wizard. Select Android and iOS targets.
2. Open shared/build.gradle.kts and find the kotlin { } block.
3. Add a new function in commonMain that returns "KMP is ready" and call it from both apps.
4. Build and confirm both apps show your message.