在 Android Paging3 中,可变页面大小可以通过使用 RemoteMediator
和 PagingConfig
来实现。下面是一个示例代码:
首先,创建一个 CustomPagingSource
类作为你的数据源:
class CustomPagingSource(private val apiService: ApiService) : PagingSource() {
override suspend fun load(params: LoadParams): LoadResult {
try {
val nextPage = params.key ?: 1
val response = apiService.getItems(nextPage, params.loadSize)
val items = response.items
val prevKey = if (nextPage == 1) null else nextPage - 1
val nextKey = nextPage + 1
return LoadResult.Page(
data = items,
prevKey = prevKey,
nextKey = nextKey
)
} catch (e: Exception) {
return LoadResult.Error(e)
}
}
override fun getRefreshKey(state: PagingState): Int? {
// 使用刷新键来重置分页索引
return 1
}
}
然后,创建一个 CustomRemoteMediator
类作为 RemoteMediator
的实现:
class CustomRemoteMediator(private val apiService: ApiService) : RemoteMediator() {
override suspend fun load(loadType: LoadType, state: PagingState): MediatorResult {
try {
val loadKey = when (loadType) {
LoadType.REFRESH -> null
LoadType.PREPEND -> return MediatorResult.Success(endOfPaginationReached = true)
LoadType.APPEND -> {
val lastItem = state.lastItemOrNull()
lastItem?.pageNumber ?: return MediatorResult.Success(endOfPaginationReached = true)
}
}
val response = apiService.getItems(loadKey ?: 1, state.config.pageSize)
val items = response.items
// 根据 loadType 来处理数据源和键
val prevKey = if (loadType == LoadType.REFRESH) null else loadKey?.minus(1)
val nextKey = if (items.isEmpty()) null else loadKey?.plus(1)
// 清空数据库中的所有数据
if (loadType == LoadType.REFRESH) {
// 移除所有缓存数据
// database.itemDao().clearAllItems()
}
// 将数据保存到数据库中
// database.itemDao().saveItems(items)
return MediatorResult.Success(endOfPaginationReached = items.isEmpty())
} catch (e: Exception) {
return MediatorResult.Error(e)
}
}
}
最后,在你的 ViewModel 中使用 PagingConfig
来设置页面大小和预取距离,并将 CustomRemoteMediator
和 CustomPagingSource
与 Pager
结合使用:
val pagingSource = CustomPagingSource(apiService)
val pagerConfig = PagingConfig(
pageSize = 10, // 设置页面大小
prefetchDistance = 2, // 设置预取距离
enablePlaceholders = false // 禁用占位符
)
val remoteMediator = CustomRemoteMediator(apiService)
val pager = Pager(
config = pagerConfig,
remoteMediator = remoteMediator,
pagingSourceFactory = { pagingSource }
).liveData
这样,你就可以使用可变页面大小的 Android Paging3 解决方案了。