2nd/10_Wiki/Topic_Programming/Coding/Android_Paging_3_Patterns.md

id, title, category, status, source_trust_level, verification_status, created_at, updated_at, tags, tech_stack, applied_in, aliases

id	title	category	status	source_trust_level	verification_status	created_at	updated_at	tags	tech_stack	applied_in	aliases
android-paging-3-patterns	Android Paging 3 — 효율적 페이지네이션	Coding	draft	B	conceptual	2026-05-09	2026-05-09	android paging list vibe-coding	language applicable_to Kotlin / Jetpack Paging 3 Android		PagingSource RemoteMediator PagingData LazyColumn

Android Paging 3

큰 list 를 chunk 로 fetch + 캐시 + 무한 스크롤. PagingSource (단일 source) 또는 RemoteMediator + Room (network + DB) 두 패턴. Compose / RecyclerView 모두 지원.

📖 핵심 개념

• PagingSource: load(params) → PagingSourceLoadResult.
• Pager: configuration (pageSize, prefetch).
• PagingData: ViewModel 에서 Compose / Adapter 로 흐름.

💻 코드 패턴

단일 PagingSource (network only)

class UserPagingSource(private val api: UserApi) : PagingSource<Int, User>() {
    override fun getRefreshKey(state: PagingState<Int, User>): Int? {
        return state.anchorPosition?.let { state.closestPageToPosition(it)?.prevKey?.plus(1) }
    }

    override suspend fun load(params: LoadParams<Int>): LoadResult<Int, User> = try {
        val page = params.key ?: 1
        val res = api.fetchUsers(page = page, size = params.loadSize)
        LoadResult.Page(
            data = res.items,
            prevKey = if (page == 1) null else page - 1,
            nextKey = if (res.items.isEmpty()) null else page + 1,
        )
    } catch (e: IOException) {
        LoadResult.Error(e)
    }
}

class UserViewModel(api: UserApi) : ViewModel() {
    val users: Flow<PagingData<User>> = Pager(
        config = PagingConfig(pageSize = 20, prefetchDistance = 3),
        pagingSourceFactory = { UserPagingSource(api) }
    ).flow.cachedIn(viewModelScope)
}

Compose 사용

@Composable
fun UserList(viewModel: UserViewModel) {
    val users = viewModel.users.collectAsLazyPagingItems()

    LazyColumn {
        items(users.itemCount, key = users.itemKey { it.id }) { index ->
            users[index]?.let { UserRow(it) }
        }

        when (val s = users.loadState.append) {
            is LoadState.Loading -> item { Spinner() }
            is LoadState.Error -> item { ErrorRow(s.error) { users.retry() } }
            else -> Unit
        }
    }
}

RemoteMediator (network + DB cache)

@OptIn(ExperimentalPagingApi::class)
class UserRemoteMediator(
    private val api: UserApi, private val db: AppDb
) : RemoteMediator<Int, UserEntity>() {

    override suspend fun load(loadType: LoadType, state: PagingState<Int, UserEntity>): MediatorResult {
        try {
            val page = when (loadType) {
                LoadType.REFRESH -> 1
                LoadType.PREPEND -> return MediatorResult.Success(endOfPaginationReached = true)
                LoadType.APPEND -> {
                    val last = state.lastItemOrNull() ?: return MediatorResult.Success(true)
                    last.page + 1
                }
            }
            val res = api.fetchUsers(page = page, size = state.config.pageSize)
            db.withTransaction {
                if (loadType == LoadType.REFRESH) db.userDao().clear()
                db.userDao().upsertAll(res.items.map { it.toEntity(page) })
            }
            return MediatorResult.Success(endOfPaginationReached = res.items.isEmpty())
        } catch (e: Exception) {
            return MediatorResult.Error(e)
        }
    }
}

// ViewModel
val users = Pager(
    config = PagingConfig(pageSize = 20),
    remoteMediator = UserRemoteMediator(api, db),
    pagingSourceFactory = { db.userDao().pagingSource() }
).flow.cachedIn(viewModelScope)

🤔 의사결정 기준

상황	패턴
Network only, 캐시 불필요	PagingSource
Network + DB 캐시 / 오프라인	RemoteMediator + Room
검색 (key 가 string)	PagingSource<String, ...>
Cursor pagination	key = cursor
작은 list (50개 미만)	Paging 불필요 — 그냥 Flow

❌ 안티패턴

• cachedIn 없이: configuration change 마다 새 fetch. cachedIn(viewModelScope).
• getRefreshKey 잘못: refresh 시 첫 page 로 다시 → 사용자 위치 잃음.
• key 로 unstable id (timestamp): 같은 row 가 다른 page 에 나타남.
• error 상태 무시: 사용자 멈춤 모름. retry button.
• endOfPaginationReached 잘못 판정: 무한 fetch 또는 일찍 멈춤.

🤖 LLM 활용 힌트

• 신규 = Paging 3 + Compose collectAsLazyPagingItems.
• offline 필요 = RemoteMediator.

🔗 관련 문서

• Android_Room_Patterns
• React_Virtualization_Lists