[G1-Sync] Manual knowledge update

10_Wiki/Topics/Coding/Android_Lifecycle_Aware_Components.md

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+---
+id: android-lifecycle-aware-components
+title: Android Lifecycle-Aware Components
+category: Coding
+status: draft
+source_trust_level: B
+verification_status: conceptual
+created_at: 2026-05-09
+updated_at: 2026-05-09
+tags: [android, lifecycle, vibe-coding]
+tech_stack: { language: "Kotlin / Jetpack", applicable_to: ["Android"] }
+applied_in: []
+aliases: [DefaultLifecycleObserver, lifecycleScope, repeatOnLifecycle]
+---
+
+# Lifecycle-Aware Components
+
+> Activity / Fragment 의 lifecycle 상태에 자동 반응. 메모리 leak / 화면 회전 / 백그라운드 처리 사고의 90%를 막아줌.
+
+## 📖 핵심 개념
+- Lifecycle.State: INITIALIZED → CREATED → STARTED → RESUMED → DESTROYED.
+- 일반적으로 STARTED 이상에서만 UI 작업.
+- DefaultLifecycleObserver: lifecycle 메서드 override.
+
+## 💻 코드 패턴
+
+### Observer 등록
+```kotlin
+class CameraController : DefaultLifecycleObserver {
+    override fun onStart(owner: LifecycleOwner) { open() }
+    override fun onStop(owner: LifecycleOwner) { close() }
+}
+
+// Fragment / Activity
+class CameraFragment : Fragment() {
+    private val controller = CameraController()
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        viewLifecycleOwner.lifecycle.addObserver(controller)
+        // viewLifecycleOwner — view 살아있는 동안 (Fragment 인스턴스보다 짧음)
+    }
+}
+```
+
+### repeatOnLifecycle — flow 수집
+```kotlin
+class ProfileFragment : Fragment() {
+    override fun onViewCreated(...) {
+        viewLifecycleOwner.lifecycleScope.launch {
+            viewLifecycleOwner.repeatOnLifecycle(Lifecycle.State.STARTED) {
+                viewModel.user.collect { render(it) }
+            }
+        }
+    }
+}
+```
+STARTED 이전 / STOP 이후 collect 안 함. 자동 cancel + restart.
+
+### Compose 통합
+```kotlin
+@Composable
+fun ProfileScreen(viewModel: ProfileViewModel) {
+    val user by viewModel.user.collectAsStateWithLifecycle()
+    // STARTED 이상일 때만 collect
+}
+```
+
+### Custom OnLifecycleEvent
+```kotlin
+DisposableEffect(lifecycleOwner) {
+    val observer = LifecycleEventObserver { _, event ->
+        when (event) {
+            Lifecycle.Event.ON_START -> startTracking()
+            Lifecycle.Event.ON_STOP -> stopTracking()
+            else -> {}
+        }
+    }
+    lifecycleOwner.lifecycle.addObserver(observer)
+    onDispose { lifecycleOwner.lifecycle.removeObserver(observer) }
+}
+```
+
+## 🤔 의사결정 기준
+| Owner | 사용처 |
+|---|---|
+| `viewLifecycleOwner` (Fragment) | view 가 살아있는 동안 (대부분) |
+| `lifecycle` (Activity/Fragment 자체) | 인스턴스 lifecycle (Fragment 인스턴스 > view) |
+| `LocalLifecycleOwner` (Compose) | composition 안에서 |
+| Service | LifecycleService 또는 manual |
+
+## ❌ 안티패턴
+- **Fragment 에서 `lifecycle` 대신 `viewLifecycleOwner` 안 씀**: view destroy 후에도 observer 동작 → leak.
+- **STARTED 가 아닌 CREATED 에서 UI 갱신**: view 가 아직 inflate 안 됨 → crash.
+- **lifecycleScope.launch 만, repeatOnLifecycle 없음**: 백그라운드에서도 collect → 메모리.
+- **observer 제거 안 함 (DisposableEffect 미사용)**: 의도적 추가만 하고 제거 누락.
+- **Compose 에서 collectAsState (lifecycle 무시)**: 백그라운드 수집. `collectAsStateWithLifecycle` 사용.
+
+## 🤖 LLM 활용 힌트
+- Fragment 코드는 viewLifecycleOwner 가 디폴트.
+- Compose 는 collectAsStateWithLifecycle + LocalLifecycleOwner.
+
+## 🔗 관련 문서
+- [[Android_Kotlin_Coroutines_Scopes]]
+- [[Android_Flow_StateFlow_SharedFlow]]