我已经按照代码实验室在我的应用程序中实现了 Paging 3，并通过以下方式添加了一个带有重试按钮的页脚withLoadStateHeaderAndFooter：
recycler_view_results.adapter = adapter.withLoadStateHeaderAndFooter(
header = UnsplashLoadStateAdapter { adapter.retry() },
footer = UnsplashLoadStateAdapter { adapter.retry() }
)
当我单击页脚 ViewHolder 中的重试按钮时，adapter.retry()确实调用了，所以那里的设置是正确的。load但是，此方法永远不会像通常那样调用我的 PagingSource方法。
我的 PagingSource （我检查了LoadResult.Error在错误情况下是否正确返回）：
class UnsplashPagingSource(
private val unsplashApi: UnsplashApi,
private val query: String
) : PagingSource<Int, UnsplashPhoto>() {
override suspend fun load(params: LoadParams<Int>): LoadResult<Int, UnsplashPhoto> {
val position = params.key ?: UNSPLASH_STARTING_PAGE_INDEX
return try {
val response = unsplashApi.searchPhotos(query, position, params.loadSize)
val photos = response.results
LoadResult.Page(
data = photos,
prevKey = if (position == UNSPLASH_STARTING_PAGE_INDEX) null else position - 1,
nextKey = if (photos.isEmpty()) null else position + 1
)
} catch (exception: IOException) {
return LoadResult.Error(exception)
} catch (exception: HttpException) {
return LoadResult.Error(exception)
}
}
}
我的存储库：
class UnsplashRepository @Inject constructor(private val unsplashApi: UnsplashApi) {
fun getSearchResultStream(query: String): Flow<PagingData<UnsplashPhoto>> {
return Pager(
config = PagingConfig(
pageSize = NETWORK_PAGE_SIZE,
enablePlaceholders = false
),
pagingSourceFactory = { UnsplashPagingSource(unsplashApi, query) }
).flow
}
companion object {
private const val NETWORK_PAGE_SIZE = 20
}
}
在我的片段中，我这样做：
private fun searchPhotos(query: String) {
searchJob?.cancel()
searchJob = lifecycleScope.launch {
viewModel.searchPhotos(query).collectLatest {
adapter.submitData(it)
}
}
}
有趣的是，空列表的重试按钮有效：
retry_button.setOnClickListener {
adapter.retry()
// this works
}