Kotlin multiplatform project

Question

I want to write a common library using Kotin multiplatform that can be used on android and on ios . This library will have dependencies for each platform, for eg: on android I want to add jsoup as a dependency and on ios I want to add swiftsoup

For android adding java libraries as dependencies is rather easy, but for ios I could not find a way.

The question is: how can I add a swift library as a dependency to this project for ios ?

or can somebody point me to a working project as an example? I could not find anything on the internet that could solve my issue.

build.gradle.kts :

import org.jetbrains.kotlin.gradle.plugin.mpp.KotlinNativeTarget

    val serializationVersion = "0.20.0"
    val kotlinVersion = "1.3.72"

    plugins {
        kotlin("multiplatform") version kotlinVersion
        kotlin("plugin.serialization") version kotlinVersion
    }

    buildscript {
        dependencies {
            classpath("org.jetbrains.kotlin:kotlin-serialization:$kotlinVersion")
        }
    }

    repositories {
        jcenter()
        mavenCentral()
    }

    kotlin {
        //select iOS target platform depending on the Xcode environment variables
        val iOSTarget: (String, KotlinNativeTarget.() -> Unit) -> KotlinNativeTarget =
                if (System.getenv("SDK_NAME")?.startsWith("iphoneos") == true)
                    ::iosArm64
                else
                    ::iosX64

        iOSTarget("ios") {
            binaries {
                framework {
                    baseName = "SharedCode"
                }
            }
        }

        jvm("android")

        sourceSets["commonMain"].dependencies {
            implementation("org.jetbrains.kotlin:kotlin-stdlib-common")
            implementation("org.jetbrains.kotlinx:kotlinx-serialization-runtime-common:$serializationVersion")
        }

        sourceSets["androidMain"].dependencies {
            implementation("org.jetbrains.kotlin:kotlin-stdlib")
            implementation("org.jsoup:jsoup:1.13.1")
            implementation("org.jetbrains.kotlinx:kotlinx-serialization-runtime:$serializationVersion")
        }

        sourceSets["iosMain"].dependencies {
            implementation("org.jetbrains.kotlinx:kotlinx-serialization-runtime-native:$serializationVersion")
        }

    }

    val packForXcode by tasks.creating(Sync::class) {
        group = "build"

        //selecting the right configuration for the iOS framework depending on the Xcode environment variables
        val mode = System.getenv("CONFIGURATION") ?: "DEBUG"
        val framework = kotlin.targets.getByName<KotlinNativeTarget>("ios").binaries.getFramework(mode)

        inputs.property("mode", mode)
        dependsOn(framework.linkTask)

        val targetDir = File(buildDir, "xcode-frameworks")
        from({ framework.outputDirectory })
        into(targetDir)

        doLast {
            val gradlew = File(targetDir, "gradlew")
            gradlew.writeText("#!/bin/bash\nexport 'JAVA_HOME=${System.getProperty("java.home")}'\ncd '${rootProject.rootDir}'\n./gradlew \$@\n")
            gradlew.setExecutable(true)
        }
    }

    tasks.getByName("build").dependsOn(packForXcode)

Answer 1

You can't use Swift dependencies in Kotlin unless they are compatible with Objective-C. If you want to talk to them directly, you'll need to point to them with cinterop. Alternatively, you can create interfaces in Kotlin, or take lambdas, that are implemented by Swift code, and avoid cinterop.

https://kotlinlang.org/docs/reference/native/objc_interop.html

We pass in a lot of implementations in one of our example apps: https://github.com/touchlab/DroidconKotlin/blob/master/iosApp/iosApp/app/AppDelegate.swift#L33