[G1-Sync] Manual knowledge update

2026-05-09 21:08:02 +09:00
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+---
+id: mobile-kmp-compose
+title: Kotlin Multiplatform / Compose Multiplatform
+category: Coding
+status: draft
+source_trust_level: B
+verification_status: conceptual
+created_at: 2026-05-09
+updated_at: 2026-05-09
+tags: [mobile, kotlin, kmp, compose, vibe-coding]
+tech_stack: { language: "Kotlin", applicable_to: ["iOS", "Android", "Desktop", "Web"] }
+applied_in: []
+aliases: [KMP, Kotlin Multiplatform, Compose Multiplatform, expect/actual, KMM]
+---
+
+# Kotlin Multiplatform (KMP) + Compose Multiplatform
+
+> Android / iOS / Desktop / Web 같은 비즈니스 로직 (KMP). UI 도 공유 가능 (Compose Multiplatform). **Native UI 가 strict 면 KMP 만, fast share 면 둘 다**.
+
+## 📖 핵심 개념
+- KMP: 비즈니스 로직 (data, network, repository) 공유.
+- Compose Multiplatform: UI 도 같은 코드.
+- expect/actual: platform-specific.
+- iOS = framework / Cocoapods 으로 import.
+
+## 💻 코드 패턴
+
+### 폴더 (gradle)
+```
+shared/
+  src/
+    commonMain/   # 모든 platform
+    androidMain/  # Android only
+    iosMain/      # iOS only
+    desktopMain/  # JVM desktop
+    jsMain/       # Web
+androidApp/
+iosApp/
+desktopApp/
+```
+
+### shared module (build.gradle.kts)
+```kotlin
+plugins {
+    kotlin("multiplatform")
+    id("com.android.library")
+}
+
+kotlin {
+    androidTarget()
+    iosX64()
+    iosArm64()
+    iosSimulatorArm64()
+    jvm("desktop")
+    
+    cocoapods {
+        version = "1.0"
+        summary = "Shared module"
+        homepage = "..."
+        ios.deploymentTarget = "17.0"
+        framework {
+            baseName = "Shared"
+            isStatic = true
+        }
+    }
+    
+    sourceSets {
+        commonMain.dependencies {
+            implementation("io.ktor:ktor-client-core:2.3.0")
+            implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.6.0")
+            implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.7.0")
+        }
+        androidMain.dependencies {
+            implementation("io.ktor:ktor-client-okhttp:2.3.0")
+        }
+        iosMain.dependencies {
+            implementation("io.ktor:ktor-client-darwin:2.3.0")
+        }
+    }
+}
+```
+
+### Common code
+```kotlin
+// shared/commonMain/Repository.kt
+class UserRepository(private val client: HttpClient) {
+    suspend fun fetchUser(id: String): User {
+        return client.get("$BASE/users/$id").body()
+    }
+}
+
+@Serializable
+data class User(val id: String, val email: String, val name: String)
+```
+
+### expect/actual (platform 별 구현)
+```kotlin
+// commonMain
+expect class Platform() {
+    val name: String
+}
+
+// androidMain
+actual class Platform actual constructor() {
+    actual val name: String = "Android ${android.os.Build.VERSION.SDK_INT}"
+}
+
+// iosMain
+import platform.UIKit.UIDevice
+actual class Platform actual constructor() {
+    actual val name: String = "iOS ${UIDevice.currentDevice.systemVersion}"
+}
+```
+
+### Android 사용
+```kotlin
+// androidApp
+val repo = UserRepository(httpClient)
+val user = lifecycleScope.launch { repo.fetchUser("u1") }
+```
+
+### iOS 사용 — Swift
+```swift
+import Shared
+
+let repo = UserRepository(client: ...)
+Task {
+    let user = try await repo.fetchUser(id: "u1")
+}
+
+// Kotlin suspend → Swift async/await 자동 (KMP 1.9+)
+```
+
+### Compose Multiplatform (UI 공유)
+```kotlin
+// shared/commonMain/App.kt
+import androidx.compose.runtime.*
+import androidx.compose.material3.*
+
+@Composable
+fun App(repo: UserRepository) {
+    var user by remember { mutableStateOf<User?>(null) }
+    LaunchedEffect(Unit) { user = repo.fetchUser("u1") }
+    
+    Scaffold { padding ->
+        Text(user?.name ?? "Loading", modifier = Modifier.padding(padding))
+    }
+}
+```
+
+```swift
+// iosApp/iOSApp.swift
+import SwiftUI
+import Shared
+
+struct ContentView: View {
+    var body: some View {
+        ComposeView()
+            .ignoresSafeArea(.all, edges: .bottom)
+    }
+}
+
+struct ComposeView: UIViewControllerRepresentable {
+    func makeUIViewController(context: Context) -> UIViewController {
+        return Main_iosKt.MainViewController()
+    }
+    func updateUIViewController(_ vc: UIViewController, context: Context) {}
+}
+```
+
+### Network — Ktor Client
+```kotlin
+val client = HttpClient {
+    install(ContentNegotiation) {
+        json(Json { ignoreUnknownKeys = true })
+    }
+    defaultRequest {
+        url(BASE_URL)
+        header("Authorization", "Bearer $token")
+    }
+}
+```
+
+### Database — SQLDelight
+```kotlin
+// shared/commonMain/sqldelight/com/acme/AppDatabase.sq
+CREATE TABLE User (
+  id TEXT PRIMARY KEY NOT NULL,
+  email TEXT NOT NULL
+);
+
+selectAll:
+SELECT * FROM User;
+
+insert:
+INSERT OR REPLACE INTO User VALUES (?, ?);
+```
+
+```kotlin
+val db = AppDatabase(driver)
+db.userQueries.insert("u1", "a@b.com")
+val users = db.userQueries.selectAll().executeAsList()
+```
+
+### State management
+```kotlin
+class UserViewModel(private val repo: UserRepository) {
+    private val _state = MutableStateFlow<UiState>(UiState.Loading)
+    val state: StateFlow<UiState> = _state
+    
+    suspend fun load(id: String) {
+        _state.value = UiState.Loading
+        try {
+            _state.value = UiState.Success(repo.fetchUser(id))
+        } catch (e: Exception) {
+            _state.value = UiState.Error(e.message ?: "")
+        }
+    }
+}
+
+sealed class UiState {
+    object Loading : UiState()
+    data class Success(val user: User) : UiState()
+    data class Error(val msg: String) : UiState()
+}
+```
+
+### iOS 호출 — coroutines 변환
+```
+// KMP 1.9+ 자동 async/await.
+// 또는 NativeCoroutines 라이브러리 — Combine / async stream.
+```
+
+### Test (commonTest)
+```kotlin
+class UserRepositoryTest {
+    @Test
+    fun fetchUser() = runTest {
+        val mock = MockEngine { ... }
+        val repo = UserRepository(HttpClient(mock))
+        val user = repo.fetchUser("u1")
+        assertEquals("u1", user.id)
+    }
+}
+```
+
+→ JVM 에서 실행 (commonTest), iOS / Android target 에 자동 적용.
+
+### Trade-offs
+```
+KMP 비즈니스 로직만:
+ Native UI 강력 / 잘 쓰면 빠름
+ iOS / Android 가 Swift / Kotlin 그대로
+- UI 코드 두 번
+
+Compose Multiplatform:
+ UI 도 한 코드
+- iOS UI 가 Material — Apple Human Interface 와 차이
+- 일부 native 기능 어려움 (camera, notification)
+```
+
+## 🤔 의사결정 기준
+| 상황 | 추천 |
+|---|---|
+| Logic 만 공유 | KMP only |
+| Logic + UI 같이 | Compose Multiplatform |
+| Native UX 강 critical | KMP only |
+| Internal tool / B2B | Compose MP |
+| Consumer app | KMP + native UI |
+| Cross-platform alternative | React Native / Flutter |
+
+## ❌ 안티패턴
+- **Compose iOS = Material design 그대로**: HIG 위반. 별 styling.
+- **Common code 안 platform 의존**: 빌드 깨짐. expect/actual.
+- **iOS 의 Combine / SwiftUI 통합 무시**: NativeCoroutines.
+- **Cocoapods + SPM 혼합**: 한 가지 선택.
+- **빌드 시간 무시**: KMP 가 처음 빌드 길음.
+- **Native API + KMP 의존**: 양쪽 의존. Either / Or.
+- **Web target 가정 prod ready**: Compose Web 은 아직 alpha.
+
+## 🤖 LLM 활용 힌트
+- 비즈니스 로직 = KMP, UI = native (대부분 case).
+- Ktor + SQLDelight + kotlinx-serialization 3종 표준.
+- expect/actual = platform-specific.
+
+## 🔗 관련 문서
+- [[Android_Compose_State_Hoisting]]
+- [[iOS_SwiftUI_State_Property_Wrappers]]
+- [[React_Native_Bridge_Performance]]