I am using RemoteMediator in my android compose project.

我在我的Android Compose项目中使用RemoteMediator。

The implementation looks something like:

该实现类似于：

@OptIn(ExperimentalPagingApi::class)
class MessagesRemoteMediator(
    private val db : MessagesDB,
    private val messageService : MessageService,
    private val query : Long
) : RemoteMediator<Int, MessageDb>() {


    override suspend fun initialize(): InitializeAction {
        // checking if refresh is needed
         ...
    }


    override suspend fun load(
        loadType: LoadType,
        state: PagingState<Int, MessageDb>
    ): MediatorResult {

        return try {

            val response = when (loadType) {
                LoadType.REFRESH -> {
                   
                    messageService.refreshChatMessages(query)

                }
                LoadType.PREPEND -> {
                    //add new messages to start of reversed list

                    val firstItem = state.firstItemOrNull()
                        ?: return MediatorResult.Success(endOfPaginationReached = true)

                    messageService.getNewChatMessages(firstItem.timeStamp, query)

                }
                LoadType.APPEND -> {

                    // add older messages to end of reversed list

                    val lastItem = state.lastItemOrNull()
                        ?: return MediatorResult.Success(endOfPaginationReached = true)

                    messageService.getOldChatMessages(lastItem.timeStamp, query)

                }
            }

             db.withTransaction {

                db.dao.insertNewMessages(response.map {dto ->
                    dto.toMessageDb()
                })
            }

            //Does not work without delay
            if(loadType == LoadType.REFRESH)
                delay(3000)

            MediatorResult.Success(endOfPaginationReached = response.isEmpty())

        } catch (e: Exception){
            Log.d("CHECKTAGS", e.stackTraceToString())
            MediatorResult.Error(e)
        }

    }
}

I am getting response from my server on initial refresh. And new data is inserted in Room's db. Still, prepend and append calls bump into null checks and pagination stops.

我在初始刷新时收到来自服务器的响应。并将新数据插入到Room的数据库中。尽管如此，Preend和Append调用仍会遇到空检查和分页停止。

It does work if I add delay after initial refresh. Is there a problem in remote mediator's code, or issue could be with lazy column in compose function?

如果我在初始刷新后添加延迟，它确实起作用。是远程中介器的代码有问题，还是组合函数中的惰性列有问题？

Update
Recreating project on XML gives same result.
Guess I could rely on db keys solution, described here
post

在XML上更新重新创建项目会产生相同的结果。我想我可以依靠db key解决方案，这里的帖子描述了

Still I don't understand why lastItemOrNull() does not work. For initial population of db I do not use it. It is being called only after initial data is being saved to room.

不过，我还是不明白为什么lastItemOrNull()不起作用。对于数据库的初始群体，我不使用它。只有在将初始数据保存到房间后才会调用它。