Kotlin Multiplatform 실전 가이드

KMP 구조 — 공유 레이어와 플랫폼 레이어

KMP 프로젝트 구조 및 expect/actual 예시
// build.gradle.kts — KMP 멀티플랫폼 설정
kotlin {
    androidTarget()
    iosX64()
    iosArm64()
    iosSimulatorArm64()

    sourceSets {
        commonMain.dependencies {
            implementation("io.ktor:ktor-client-core:2.3.7")
            implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.6.2")
            implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.7.3")
        }
        androidMain.dependencies {
            implementation("io.ktor:ktor-client-okhttp:2.3.7")
        }
        iosMain.dependencies {
            implementation("io.ktor:ktor-client-darwin:2.3.7")
        }
    }
}

// commonMain/Platform.kt — expect 선언
expect fun getPlatformName(): String
expect class PlatformLogger() {
    fun log(message: String)
}

// androidMain/Platform.android.kt — actual 구현
actual fun getPlatformName(): String = "Android ${android.os.Build.VERSION.SDK_INT}"
actual class PlatformLogger actual constructor() {
    actual fun log(message: String) = android.util.Log.d("KMP", message)
}

// iosMain/Platform.ios.kt — actual 구현
actual fun getPlatformName(): String = UIDevice.currentDevice.systemName()
actual class PlatformLogger actual constructor() {
    actual fun log(message: String) = NSLog("%@", message)
}

Shared Module 실전 예시 — Repository 패턴

commonMain — 공유 Repository 및 API 클라이언트
// commonMain/data/UserRepository.kt
import io.ktor.client.*
import io.ktor.client.call.*
import io.ktor.client.request.*
import kotlinx.serialization.Serializable

@Serializable
data class User(
    val id: Int,
    val name: String,
    val email: String
)

class UserRepository(private val client: HttpClient) {
    suspend fun getUser(id: Int): Result<User> {
        return runCatching {
            client.get("https://api.example.com/users/$id").body<User>()
        }
    }

    suspend fun getUsers(): Result<List<User>> {
        return runCatching {
            client.get("https://api.example.com/users").body<List<User>>()
        }
    }
}

// commonMain/di/HttpClientFactory.kt
import io.ktor.client.*
import io.ktor.client.plugins.contentnegotiation.*
import io.ktor.serialization.kotlinx.json.*

fun createHttpClient(): HttpClient = HttpClient {
    install(ContentNegotiation) {
        json()
    }
}

Compose Multiplatform — UI도 공유하려면

iOS 통합 — Swift에서 KMP 모듈 사용하기

iOS — XCFramework 빌드 및 Swift에서 KMP 호출
# XCFramework 빌드 (Gradle 태스크)
./gradlew assembleXCFramework
# → build/XCFrameworks/release/shared.xcframework 생성

# Xcode에서 shared.xcframework를 Frameworks에 추가 후

// Swift에서 KMP 코드 호출
import shared  // KMP 모듈 import

class UserViewModel: ObservableObject {
    @Published var user: User?
    @Published var errorMessage: String?

    private let repository = UserRepository(client: createHttpClient())

    func loadUser(id: Int) {
        // Kotlin suspend 함수 → Swift async/await 변환
        Task {
            do {
                // KotlinInt로 변환 필요
                let result = try await repository.getUser(id: Int32(id))
                await MainActor.run {
                    self.user = result
                }
            } catch {
                await MainActor.run {
                    self.errorMessage = error.localizedDescription
                }
            }
        }
    }
}

실무 적용 사례와 도입 판단 기준