If your project does not have a deep dependency on the paging3 library, I recommend implementing a simple paging library yourself to avoid all the weird features of paging3. The paging library needs the view layer and the model layer to work together. It doesn't make sense to encapsulate these together.

!simple paged list for jetpack compose

!simple paged list for jetpack compose

1.RemoteList.kt

// Model layer: remotePagingList()
package com.fishhawk.lisu.data.network.base

import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.channels.Channel
import kotlinx.coroutines.channels.awaitClose
import kotlinx.coroutines.flow.Flow
import kotlinx.coroutines.flow.callbackFlow
import kotlinx.coroutines.flow.flowOn
import kotlinx.coroutines.flow.receiveAsFlow
import kotlinx.coroutines.launch

sealed interface RemoteListAction<out T> {
    data class Mutate<T>(val transformer: (MutableList<T>) -> MutableList<T>) : RemoteListAction<T>
    object Reload : RemoteListAction<Nothing>
    object RequestNextPage : RemoteListAction<Nothing>
}

typealias RemoteListActionChannel<T> = Channel<RemoteListAction<T>>

suspend fun <T> RemoteListActionChannel<T>.mutate(transformer: (MutableList<T>) -> MutableList<T>) {
    send(RemoteListAction.Mutate(transformer))
}

suspend fun <T> RemoteListActionChannel<T>.reload() {
    send(RemoteListAction.Reload)
}

suspend fun <T> RemoteListActionChannel<T>.requestNextPage() {
    send(RemoteListAction.RequestNextPage)
}

class RemoteList<T>(
    private val actionChannel: RemoteListActionChannel<T>,
    val value: Result<PagedList<T>>?,
) {
    suspend fun mutate(transformer: (MutableList<T>) -> MutableList<T>) =
        actionChannel.mutate(transformer)

    suspend fun reload() = actionChannel.reload()
    suspend fun requestNextPage() = actionChannel.requestNextPage()
}

data class PagedList<T>(
    val list: List<T>,
    val appendState: Result<Unit>?,
)

data class Page<Key : Any, T>(
    val data: List<T>,
    val nextKey: Key?,
)

fun <Key : Any, T> remotePagingList(
    startKey: Key,
    loader: suspend (Key) -> Result<Page<Key, T>>,
    onStart: ((actionChannel: RemoteListActionChannel<T>) -> Unit)? = null,
    onClose: ((actionChannel: RemoteListActionChannel<T>) -> Unit)? = null,
): Flow<RemoteList<T>> = callbackFlow {
    val dispatcher = Dispatchers.IO.limitedParallelism(1)

    val actionChannel = Channel<RemoteListAction<T>>()

    var listState: Result<Unit>? = null
    var appendState: Result<Unit>? = null
    var value: MutableList<T> = mutableListOf()
    var nextKey: Key? = startKey

    onStart?.invoke(actionChannel)

    suspend fun mySend() {
        send(
            RemoteList(
                actionChannel = actionChannel,
                value = listState?.map {
                    PagedList(
                        appendState = appendState,
                        list = value,
                    )
                },
            )
        )
    }

    fun requestNextPage() = launch(dispatcher) {
        nextKey?.let { key ->
            appendState = null
            mySend()
            loader(key)
                .onSuccess {
                    value.addAll(it.data)
                    nextKey = it.nextKey
                    listState = Result.success(Unit)
                    appendState = Result.success(Unit)
                    mySend()
                }
                .onFailure {
                    if (listState?.isSuccess != true)
                        listState = Result.failure(it)
                    appendState = Result.failure(it)
                    mySend()
                }
        }
    }

    var job = requestNextPage()

    launch(dispatcher) {
        actionChannel.receiveAsFlow().flowOn(dispatcher).collect { action ->
            when (action) {
                is RemoteListAction.Mutate -> {
                    value = action.transformer(value)
                    mySend()
                }
                is RemoteListAction.Reload -> {
                    job.cancel()
                    listState = null
                    appendState = null
                    value.clear()
                    nextKey = startKey
                    mySend()
                    job = requestNextPage()
                }
                is RemoteListAction.RequestNextPage -> {
                    if (!job.isActive) job = requestNextPage()
                }
            }
        }
    }
    launch(dispatcher) {
        Connectivity.instance?.interfaceName?.collect {
            if (job.isActive) {
                job.cancel()
                job = requestNextPage()
            }
        }
    }
    awaitClose {
        onClose?.invoke(actionChannel)
    }
}

2.RepositoryExample.kt

// An example about how to use remotePagingList in repository.

private val daoFlow: StateFlow<Result<NetworkDao>?> // NetworkDao describe interfaces provided by server

suspend fun search(
    providerId: String,
    keywords: String,
) = daoFlow.filterNotNull().flatMapLatest {
    remotePagingList(
        startKey = 0,
        loader = { page ->
            it.mapCatching { dao -> dao.search(providerId, page, keywords) }
                .map { Page(it, if (it.isEmpty()) null else page + 1) }
        },
        onStart = { providerMangaListActionChannels.add(it) },
        onClose = { providerMangaListActionChannels.remove(it) },
    )
}

3.ViewModelExample.kt

// An example about how to use remotePagingList in view model.

private val _keywords = MutableStateFlow("")
val keywords = _keywords.asStateFlow()

private val _mangas =
    keywords
        .flatMapLatest { repository.search(it) }
        .stateIn(viewModelScope, SharingStarted.Eagerly, null)
        
val mangas =
    _mangas
        .filterNotNull()
        .map { it.value }
        .stateIn(viewModelScope, SharingStarted.Eagerly, null)

fun reload() {
    viewModelScope.launch {
        _mangas.value?.reload()
    }
}

fun requestNextPage() {
    viewModelScope.launch {
        _mangas.value?.requestNextPage()
    }
}

4.ComposeExample.kt

// An heavily simplified example about how to use manga in compose with a lot of.
// There are potential performance issues that can be solved by reducing the frequency of calls to onRequestNextPage.

@Composable
fun ComposeExample() {
  val mangaListResult by viewModel.mangas.collectAsState()

  StateView(
      result = mangaListResult,
      onRetry = { onAction(LibraryAction.Reload) },
      modifier = Modifier
          .padding(paddingValues)
          .fillMaxSize(),
  ) { mangaList ->
      MangaList(
          mangaList = mangaList,
          onRequestNextPage = { onAction(LibraryAction.RequestNextPage) },
      )
  }
}

@Composable
fun MangaList(
    mangaList: PagedList<MangaDto>,
    onRequestNextPage: () -> Unit,
) {
    var maxAccessed by remember { mutableStateOf(0) }
    LazyColumn {
        itemsIndexed(mangaList.list) { index, manga ->
            if (index > maxAccessed) {
                maxAccessed = index
                if (
                    mangaList.appendState?.isSuccess == true &&
                    maxAccessed < mangaList.list.size + 30
                ) {
                    onRequestNextPage()
                }
            }
            MangaCard(manga = manga)
        }

        fun itemFullWidth(content: @Composable () -> Unit) {
            item(span = { GridItemSpan(maxCurrentLineSpan) }) { Box {} }
            item(span = { GridItemSpan(maxCurrentLineSpan) }) { content() }
        }
        mangaList.appendState
            ?.onFailure { itemFullWidth { ErrorItem(it) { onRequestNextPage() } } }
            ?: itemFullWidth { LoadingItem() }
    }
}

What is Connectivity in RemoteList.kt file? I am getting error on that.

Connectivity is my helper class that watches the network connection change. It has nothing to do with paging.

I used this code in https://github.com/FishHawk/lisu-android, although it's not a simple project.

What is Connectivity in RemoteList.kt file? I am getting error on that.

Connectivity is my helper class that watches the network connection change. It has nothing to do with paging.

I used this code in https://github.com/FishHawk/lisu-android, although it's not a simple project.

Thank you very much, really good sample project.