IssueTracker

Thanks for reporting this!

Same here, any update? Stuck at alpha02 for a long time.

A few notes:

1. Should be using viewLifecyclerOwner.lifecycleScope instead of just lifecycleScope in a Fragment.
2. Cancellation is happening as a result of the fragment automatically paging over when they are initially created / added to viewpager2 (this is expected as far as I can tell)
3. Right now RemoteMediator kind of acts as a dumb callback whenever PagingSource runs out of items to load, so REFRESH error doesn't prevent remote PREPEND / APPEND. It's not clear to me yet whether it should or if we should change guidance to just handle APPEND. This is due to us changing the behavior of Remote REFRESH after the codelab was produced, so I'm very sorry for that. REFRESH is meant to handle any init that needs to happen, technically the initial network page fetch happens as a result of running out of items on the APPEND side.

e.g., Here is a modified sample from the opening post / #1's repro project that fixes the issue:

PageKeyedRemoteMediator.kt

override suspend fun load(
    loadType: LoadType,
    state: PagingState<Int, RedditPost>
): MediatorResult {
    try {
        // Get the closest item from PagingState that we want to load data around.
        val loadKey = when (loadType) {
            REFRESH -> {
                db.withTransaction {
                    postDao.deleteBySubreddit(subredditName)
                    remoteKeyDao.deleteBySubreddit(subredditName)
                }

                return MediatorResult.Success(endOfPaginationReached = false)
            }
            PREPEND -> return MediatorResult.Success(endOfPaginationReached = true)
            APPEND -> {
                // Query DB for SubredditRemoteKey for the subreddit.
                // SubredditRemoteKey is a wrapper object we use to keep track of page keys we
                // receive from the Reddit API to fetch the next or previous page.
                val remoteKey = db.withTransaction {
                    remoteKeyDao.remoteKeyByPost(subredditName)
                }

                when {
                    remoteKey == null -> null
                    // We must explicitly check if the page key is null after initial load, since the
                    // Reddit API informs the end of the list by returning null for page key, but
                    // passing a null key to Reddit API will fetch the initial page.
                    remoteKey.nextPageKey == null -> {
                        return MediatorResult.Success(endOfPaginationReached = true)
                    }
                    else -> remoteKey.nextPageKey
                }
            }
        }

        val data = redditApi.getTop(
            subreddit = subredditName,
            after = loadKey,
            before = null,
            limit = state.config.pageSize * 3
        ).data

        val items = data.children.map { it.data }

        db.withTransaction {
            remoteKeyDao.insert(SubredditRemoteKey(subredditName, data.after))
            postDao.insertAll(items)
        }

        return MediatorResult.Success(endOfPaginationReached = items.isEmpty())
    } catch (e: IOException) {
        return MediatorResult.Error(e)
    } catch (e: HttpException) {
        return MediatorResult.Error(e)
    } catch (e: CancellationException) {
        Log.d("RemoteMediator","$subredditName $loadType canceled")
        throw e
    }
}