I am working on get flow working for endless scrol...

# compose

[Timo Drick]

I am working on get flow working for endless scrolling (LazyColumnFor/LazyRowFor) lists. (Including error handling, retry and load on demand)
Maybe someone can review the code to check if this is correct (For me it works fine 🙂 but maybe i missed something escepcially with the Channel stuff)

[Timo Drick]

fun <T> Flow<T>.stateList() = Flow2StateList(this)

sealed class FlowState<out T> {
    object Loading : FlowState<Nothing>()
    class Error(val error: Throwable): FlowState<Nothing>()
    class Item<T>(val value: T): FlowState<T>()
}

class Flow2StateList<T>(
    private val flow: Flow<T>
): CoroutineScope {
    private val job = Job()
    override val coroutineContext = Dispatchers.Main + job
    val list: SnapshotStateList<FlowState<T>> = mutableStateListOf()

    private val requestItemsChannel = Channel<Int>(Channel.CONFLATED)
    private val retryChannel = Channel<Boolean>(Channel.CONFLATED)
    private var requestedListSize = 0

    init {
        launch {
            log("$this - Start collecting for $flow")
            if (requestedListSize <= 0) {
                requestedListSize = requestItemsChannel.receive()
            }
            list.add(FlowState.Loading) // set last list item to loading
            var inProgress = true

            flow.buffer(5)
                .retryWhen { cause, _ ->
                    log("Retry", cause)
                    if (inProgress) {
                        list.removeLast()
                    }
                    list.add(FlowState.Error(cause)) // Add error item to end of list
                    inProgress = true
                    return@retryWhen retryChannel.receive()
                }.collect {
                    if (inProgress) {
                        list.removeLast()
                        inProgress = false
                    }
                    list.add(FlowState.Item(it))
                    if (list.size >= requestedListSize) {
                        log("Wait until new items needed. List size: ${list.size} requested: $requestedListSize")
                        requestedListSize = requestItemsChannel.receive()
                    }
                }

            log("$this - collection ready")
        }
    }

    /**
     * Request more items to consume from the flow
     */
    internal fun requestItems(count: Int) {
        if (job.isActive) {
            launch {
                requestItemsChannel.send(list.size + count)
            }
        }
    }

    fun retry() {
        launch {
            retryChannel.send(true)
        }
    }

    protected fun finalize() {
        job.cancel()
        requestItemsChannel.cancel()
        log("$this - Channel and job canceled")
    }

}

[Timo Drick]

The idea is that you can pass the list to your LazyColumnFor