multiplatform.md

Multiplatform

This document covers using kotlin-inject in a multiplatform project. The example we'll follow is setting up an android and iOS project but the pattern should be the same for other platforms. You can check out greeter for a full sample.

Gradle

See the README for instructions on how to add kotlin-inject to your project.

Replace the kotlin-jvm plugin with the kotlin-multiplatform plugin

plugins {
    id("org.jetbrains.kotlin.multiplatform")
    id("com.google.devtools.ksp")
}

Set up targets

kotlin {
    androidTarget()

    listOf(
        iosX64(),
        iosArm64(),
        iosSimulatorArm64()
    ).forEach {
        it.binaries.framework {
            baseName = "shared"
        }
    }

    // add your project's other targets...
}

Add the runtime dependency in commonMain

sourceSets {
    commonMain {
        dependencies {
            implementation("me.tatarka.inject:kotlin-inject-runtime-kmp:0.7.0")
        }
    }
}

Note

kotlin-inject-runtime-kmp is the same as kotlin-inject-runtime aside from adding the KmpComponentCreate annotation.

Adding the compiler dependencies

When configuring KSP for use with kotlin-inject, you can choose to generate the code into:

1. The common source set (see below for the implementation of configureCommonMainKsp)
2. Each individual KMP target source set

Add the compiler dependencies in a top level dependencies block

Tip

There is a good chance that the API for adding KSP compiler dependencies will change in the future. Follow ksp#1021 for updates.

dependencies {
    // 1. Configure code generation into the common source set
    kspCommonMainMetadata(libs.kotlinInject)

    // 2. Configure code generation into each KMP target source set
    kspAndroid("me.tatarka.inject:kotlin-inject-compiler-ksp:0.7.0")
    kspIosX64("me.tatarka.inject:kotlin-inject-compiler-ksp:0.7.0")
    kspIosArm64("me.tatarka.inject:kotlin-inject-compiler-ksp:0.7.0")
    kspIosSimulatorArm64("me.tatarka.inject:kotlin-inject-compiler-ksp:0.7.0")
}

Note

Code generation can be configured for both the common source set and all target source sets, but that will likely lead to Redeclaration errors for @Component when ksp is used for common and target source sets.

If a Component is declared in the common source set, then KSP would typically be configured to generate code in the common source set. This means that the generated code will be accessible from the common source set, and any source set that depends on it.

However, certain scenarios instead require generating code for all target source sets (e.g. if a Component or any of its ancestors are an expect type, and the actual implementation provides platform specific bindings).

In those cases, while the Component might be declared in the common source set, it is not possible to create it, because the create functions are declared in each target source set.

Note

Pre Kotlin 2.0 it is possible to reference the create function from the common source set because code from a target source set was visible to the common source set. However this can lead to very subtle bugs, and starting from Kotlin 2.0 common source sets can no longer see code from target source sets.

In order to create the Component, it is necessary to declare an expect fun, and have the actual fun call the target's create function.

// common source set
@Component
abstract class MyKmpComponent

expect fun createKmp(): MyKmpComponent

// each target source set
actual fun createKmp(): MyKmpComponent = MyKmpComponent::class.create()

Creating an actual fun for each platform can be tedious, so kotlin-inject provides a KmpComponentCreate annotation.

@Component
abstract class MyKmpComponent

@KmpComponentCreate
expect fun createKmp(): MyKmpComponent

Note

Make sure you are using the kotlin-inject-runtime-kmp artifact in order to have access to the KmpComponentCreate annotation.

kotlin-inject's processor will generate an actual fun in each target's source set that calls through to the create function for MyKmpComponent. The generated code looks like this:

actual fun createKmp(): MyKmpComponent = MyKmpComponent::class.create()

The annotated expect fun's parameters will be passed to the Component's create function, so it should contain exactly the parameters that the create function expects.

Because these are regular expect/actual functions, an extension function can be used, which can be helpful for namespacing:

@KmpComponentCreate
expect fun MyKmpComponent.Companion.createKmp(): MyKmpComponent

in which case the generated code would look like:

@KmpComponentCreate
actual fun MyKmpComponent.Companion.createKmp(): MyKmpComponent = MyKmpComponent::class.create()

Shared source sets

KmpComponentCreate can be used for all shared source sets, not just commonMain.

For example, you won't be able to access the create functions in each of the ios target source sets (iosArm64, iosSimulatorArm64, etc...) from an ios shared source set.

You can define a KmpComponentCreate which will allow you to create the Component in the ios shared source set

// common source set
@Component
abstract class MyKmpComponent

// android source set
val myKmpComponent: MyKmpComponent = MyKmpComponent::class.create()

// ios source set
// the actual createKmp functions will only be generated in the targets that depend on the ios source set
@KmpComponentCreate
expect fun MyKmpComponent.Companion.createKmp(): MyKmpComponent

val myKmpComponent: MyKmpComponent = MyKmpComponent.createKmp()

Usage

Usage is the same as mentioned here.

The only difference is for projects that generate code into each KMP target source set, in which case you would use the KmpComponentCreate to create the Component when necessary.

KSP Common Source Set Configuration

kotlin {
    // add your project's targets here like in the snippet above

    configureCommonMainKsp()
}

@OptIn(ExternalVariantApi::class)
fun KotlinMultiplatformExtension.configureCommonMainKsp() {
  sourceSets.named("commonMain").configure {
    kotlin.srcDir("build/generated/ksp/metadata/commonMain/kotlin")
  }

  project.tasks.withType(KotlinCompilationTask::class.java).configureEach {
    if(name != "kspCommonMainKotlinMetadata") {
      dependsOn("kspCommonMainKotlinMetadata")
    }
  }
}