RemoteMediator 不转到下一页，分页 3 问题

Question

我的 Jetpack Compose 项目有问题。我想设置一个带有 nextPage 和 PrevPage 的 RemoteMediator，但这不能正常工作，它不显示下一页。需要注意的是，我的 Json 中没有“id”键，所以我使用 phone 数字来创建唯一键。

这是我的代码 RemoteMediator.kt

@OptIn(ExperimentalPagingApi::class)
class RemoteMediator @Inject constructor(
private val dataDb: DataDb,
private val retrofitService: RetrofitService,
) : RemoteMediator<Int, com.example.testlydiaapp.data.online.model.Result>() {

val dataDao = dataDb.dataDao()
val randomUserKeysDao = dataDb.randomUserKeysDao()

override suspend fun load(loadType: LoadType, state: PagingState<Int, com.example.testlydiaapp.data.online.model.Result>): MediatorResult {
    return try {
        val currentPage = when (loadType) {
            LoadType.REFRESH -> {
                val remoteKeys = getRemoteKeyClosestToCurrentPosition(state = state)
                remoteKeys?.nextPage?.minus(1) ?: 1
            }
            LoadType.PREPEND -> {
                val remoteKeys = getRemoteKeyForFirstTime(state = state)
                val prevPage = remoteKeys?.prevPage
                    ?: return MediatorResult.Success(
                        endOfPaginationReached = remoteKeys != null
                    )
                prevPage
            }
            LoadType.APPEND -> {
                val remoteKeys = getRemoteKeyForLastTime(state = state)
                val nextPage = remoteKeys?.nextPage
                    ?: return MediatorResult.Success(
                        endOfPaginationReached = remoteKeys != null
                    )
                nextPage
            }
        }

        val response = retrofitService.getRandomUsers(page = currentPage)
        val endOfPaginationReached = response.results.isEmpty()

        val prevPage = if (currentPage == 1) null else currentPage - 1
        val nextPage = if (endOfPaginationReached) null else currentPage + 1

        dataDb.withTransaction {
            if (loadType == LoadType.REFRESH) {
                dataDao.clearAll()
                randomUserKeysDao.clearAllRandomUsersRemoteKeys()
            }
            val keys = response.results.map { randomUser ->
                RandomUsersRemoteKeys(
                    id = randomUser.phone,
                    prevPage = prevPage,
                    nextPage = nextPage
                )
            }
            randomUserKeysDao.insertAllRandomUsersRemoteKeys(remoteKeys = keys)
            dataDao.insertRandomUserList(item = response.results)
        }
        MediatorResult.Success(endOfPaginationReached = endOfPaginationReached)
    } catch (e: Exception) {
        return MediatorResult.Error(e)
    }
}

private fun getRemoteKeyClosestToCurrentPosition(
    state: PagingState<Int, com.example.testlydiaapp.data.online.model.Result>
): RandomUsersRemoteKeys? {
    return state.anchorPosition?.let {
        state.closestItemToPosition(it)?.phone?.let { id ->
            randomUserKeysDao.getRandomUsersRemoteKeys(id = id)
        }
    }
}

private fun getRemoteKeyForFirstTime(
    state: PagingState<Int, com.example.testlydiaapp.data.online.model.Result>
): RandomUsersRemoteKeys? {
    return state.pages.firstOrNull() { it.data.isNotEmpty() }?.data?.firstOrNull()
        ?.let {
            randomUserKeysDao.getRandomUsersRemoteKeys(id = it.phone)
        }
}

private fun getRemoteKeyForLastTime(
    state: PagingState<Int, com.example.testlydiaapp.data.online.model.Result>
): RandomUsersRemoteKeys? {
    return state.pages.lastOrNull() { it.data.isNotEmpty() }?.data?.lastOrNull()
        ?.let {
            randomUserKeysDao.getRandomUsersRemoteKeys(id = it.phone)
        }
}

}

Answer 1

我找到了解决方案。

我在 RemoteMediator 的顶部添加了这个 ->

override suspend fun initialize(): InitializeAction {
    return InitializeAction.LAUNCH_INITIAL_REFRESH
}

之后，我在 LocalDb 事务中初始化了 prevPage 和 NextPage。

我通过在末尾和 MediatorKeyDao 函数上向所有 3 个函数 getRemoteKy 添加挂起来完成。

RemoteMediator 不转到下一页，分页 3 问题

RemoteMediator doesn't go next page, paging 3 problem

android

kotlin

android-jetpack-compose

android-paging-3