ルームデータベースを信頼できるソースとして使用し、 RemoteMediatorを使用して、コードラボに従って Jetpack ページング 3 ライブラリを実装しようとしています。アプリは Google Books API にクエリを実行しますが、何らかの理由で検索を実行すると、同じページに対して複数の呼び出しが行われます。たとえば、スクロールせずに火を検索すると、ログに次のように表示されます。
D/BooksRepository: new search: fire
D/BooksRemoteMediator: title: fire, page: 0
I/okhttp.OkHttpClient: --> GET https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=0
I/okhttp.OkHttpClient: <-- 200 https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=0 (648ms, unknown-length body)
D/BooksRemoteMediator: title: fire, page: 1
I/okhttp.OkHttpClient: --> GET https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=1
I/okhttp.OkHttpClient: <-- 200 https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=1 (608ms, unknown-length body)
D/BooksRemoteMediator: title: fire, page: 0
I/okhttp.OkHttpClient: --> GET https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=0
I/okhttp.OkHttpClient: <-- 200 https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=0 (629ms, unknown-length body)
D/BooksRemoteMediator: title: fire, page: 1
I/okhttp.OkHttpClient: --> GET https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=1
I/okhttp.OkHttpClient: <-- 200 https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=1 (843ms, unknown-length body)
D/BooksRemoteMediator: title: fire, page: 0
I/okhttp.OkHttpClient: --> GET https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=0
I/okhttp.OkHttpClient: <-- 200 https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=0 (527ms, unknown-length body)
D/BooksRemoteMediator: title: fire, page: 1
I/okhttp.OkHttpClient: --> GET https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=1
I/okhttp.OkHttpClient: <-- 200 https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=1 (734ms, unknown-length body)
D/BooksRemoteMediator: title: fire, page: 2
I/okhttp.OkHttpClient: --> GET https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=2
I/okhttp.OkHttpClient: <-- 200 https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=2 (783ms, unknown-length body)
D/BooksRemoteMediator: title: fire, page: 3
I/okhttp.OkHttpClient: --> GET https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=3
I/okhttp.OkHttpClient: <-- 200 https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=3 (769ms, unknown-length body)
D/BooksRemoteMediator: title: fire, page: 2
I/okhttp.OkHttpClient: --> GET https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=2
I/okhttp.OkHttpClient: <-- 200 https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=2 (521ms, unknown-length body)
D/BooksRemoteMediator: title: fire, page: 3
I/okhttp.OkHttpClient: --> GET https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=3
I/okhttp.OkHttpClient: <-- 200 https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=3 (549ms, unknown-length body)
D/BooksRemoteMediator: title: fire, page: 2
I/okhttp.OkHttpClient: --> GET https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=2
I/okhttp.OkHttpClient: <-- 200 https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=2 (966ms, unknown-length body)
D/BooksRemoteMediator: title: fire, page: 3
I/okhttp.OkHttpClient: --> GET https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=3
I/okhttp.OkHttpClient: <-- 200 https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=3 (673ms, unknown-length body)
D/BooksRemoteMediator: title: fire, page: 4
I/okhttp.OkHttpClient: --> GET https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=4
I/okhttp.OkHttpClient: <-- 200 https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=4 (634ms, unknown-length body)
D/BooksRemoteMediator: title: fire, page: 5
I/okhttp.OkHttpClient: --> GET https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=5
I/okhttp.OkHttpClient: <-- 200 https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=5 (604ms, unknown-length body)
D/BooksRemoteMediator: title: fire, page: 4
I/okhttp.OkHttpClient: --> GET https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=4
I/okhttp.OkHttpClient: <-- 200 https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=4 (632ms, unknown-length body)
D/BooksRemoteMediator: title: fire, page: 3
I/okhttp.OkHttpClient: --> GET https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=3
I/okhttp.OkHttpClient: <-- 200 https://www.googleapis.com/books/v1/volumes?q=intitle%3Afire&key=AIzaSyBxHmT9nFCp9n2uOHkS3Gcq2OO3zbxaMrw&maxResults=40&startIndex=3 (602ms, unknown-length body)
私の実装は次のようなものです：
リポジトリ:
class BooksRepository(private val service: BookService, private val database: BooksDatabase) {
companion object {
private const val NETWORK_PAGE_SIZE = 40
}
fun getSearchResultStream(
title: String = "",
author: String = "",
publisher: String = "",
isbn: String = ""
): Flow<PagingData<Book>> {
Timber.d("new search: $title")
val dbQuery = "%${title.replace(' ', '%')}%"
val pagingSourceFactory = { database.bookDao.getBooks(dbQuery, author, publisher)}
return Pager(
config = PagingConfig(
pageSize = NETWORK_PAGE_SIZE,
enablePlaceholders = false
),
remoteMediator = BooksRemoteMediator(title, author, publisher, isbn, apiKey, service, database),
pagingSourceFactory = pagingSourceFactory
).flow
}
}
リモートメディエーター:
private const val BOOKS_STARTING_PAGE_INDEX = 0
@OptIn(ExperimentalPagingApi::class)
class BooksRemoteMediator(
private val title: String?,
private val author: String?,
private val publisher: String?,
private val isbn: String?,
private val key: String,
private val service: BookService,
private val booksDatabase: BooksDatabase
) : RemoteMediator<Int, Book>() {
override suspend fun load(loadType: LoadType, state: PagingState<Int, Book>): MediatorResult {
val page = when (loadType) {
LoadType.REFRESH -> {
val remoteKeys = getRemoteKeyClosestToCurrentPosition(state)
remoteKeys?.nextKey?.minus(1) ?: BOOKS_STARTING_PAGE_INDEX
}
LoadType.PREPEND -> {
val remoteKeys = getRemoteKeyForFirstItem(state)
if (remoteKeys == null) {
// The LoadType is PREPEND so some data was loaded before,
// so we should have been able to get remote keys
// If the remoteKeys are null, then we're an invalid state and we have a bug
throw InvalidObjectException("Remote key and the prevKey should not be null")
}
// If the previous key is null, then we can't request more data
val prevKey = remoteKeys.prevKey
if (prevKey == null) {
return MediatorResult.Success(endOfPaginationReached = true)
}
remoteKeys.prevKey
}
LoadType.APPEND -> {
val remoteKeys = getRemoteKeyForLastItem(state)
if (remoteKeys == null || remoteKeys.nextKey == null) {
throw InvalidObjectException("Remote key should not be null for $loadType")
}
remoteKeys.nextKey
}
}
Timber.d("title: $title, page: $page")
val sb = StringBuilder()
if (!title.isNullOrBlank()) sb.append("$TITLE$title+")
if (!author.isNullOrBlank()) sb.append("$AUTHOR$author+")
if (!publisher.isNullOrBlank()) sb.append("$PUBLISHER$publisher+")
if (!isbn.isNullOrBlank()) sb.append("$ISBN$isbn+")
sb.setLength(sb.length - 1)
val apiQuery = sb.toString()
try {
val apiResponse = service.searchBooks(apiQuery, key, state.config.pageSize, page)
val books = apiResponse.items
val endOfPaginationReached = books.isEmpty()
booksDatabase.withTransaction {
// clear all tables in the database
if (loadType == LoadType.REFRESH) {
booksDatabase.remoteKeysDao.clearRemoteKeys()
booksDatabase.bookDao.clearBooks()
}
val prevKey = if (page == BOOKS_STARTING_PAGE_INDEX) null else page - 1
val nextKey = if (endOfPaginationReached) null else page + 1
val keys = books.map {
RemoteKeys(bookId = it.id, prevKey = prevKey, nextKey = nextKey)
}
booksDatabase.remoteKeysDao.insertAll(keys)
booksDatabase.bookDao.insert(books)
}
return MediatorResult.Success(endOfPaginationReached = endOfPaginationReached)
} catch (exception: IOException) {
return MediatorResult.Error(exception)
} catch (exception: HttpException) {
return MediatorResult.Error(exception)
}
}
private suspend fun getRemoteKeyForLastItem(state: PagingState<Int, Book>): RemoteKeys? {
// Get the last page that was retrieved, that contained items.
// From that last page, get the last item
return state.pages.lastOrNull() { it.data.isNotEmpty() }?.data?.lastOrNull()
?.let { book ->
// Get the remote keys of the last item retrieved
booksDatabase.remoteKeysDao.remoteKeysBookId(book.id)
}
}
private suspend fun getRemoteKeyForFirstItem(state: PagingState<Int, Book>): RemoteKeys? {
// Get the first page that was retrieved, that contained items.
// From that first page, get the first item
return state.pages.firstOrNull { it.data.isNotEmpty() }?.data?.firstOrNull()
?.let { book ->
// Get the remote keys of the first items retrieved
booksDatabase.remoteKeysDao.remoteKeysBookId(book.id)
}
}
private suspend fun getRemoteKeyClosestToCurrentPosition(
state: PagingState<Int, Book>
): RemoteKeys? {
// The paging library is trying to load data after the anchor position
// Get the item closest to the anchor position
return state.anchorPosition?.let { position ->
state.closestItemToPosition(position)?.id?.let { bookId ->
booksDatabase.remoteKeysDao.remoteKeysBookId(bookId)
}
}
}
}
ビューモデル:
class BookListViewModel(private val repository: BooksRepository) : ViewModel() {
private var currentQueryValue: String? = null
private var currentSearchResult: Flow<PagingData<Book>>? = null
fun searchRepo(queryString: String): Flow<PagingData<Book>> {
val lastResult = currentSearchResult
if (queryString == currentQueryValue && lastResult != null) {
return lastResult
}
currentQueryValue = queryString
val newResult: Flow<PagingData<Book>> = repository.getSearchResultStream(queryString)
.cachedIn(viewModelScope)
currentSearchResult = newResult
return newResult
}
}
断片：
class BookListFragment : Fragment() {
...
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
setHasOptionsMenu(true)
binding = FragmentBookListBinding.inflate(inflater, container, false).apply {
lifecycleOwner = viewLifecycleOwner
viewModel = bookListViewModel
}
initAdapter()
val queryString = queryArgs.split(",")
val query = savedInstanceState?.getString(LAST_SEARCH_QUERY) ?: DEFAULT_QUERY
search(query)
setHasOptionsMenu(true)
return binding.root
}
override fun onActivityCreated(savedInstanceState: Bundle?) {
super.onActivityCreated(savedInstanceState)
binding.retryButton.setOnClickListener { adapter.retry() }
}
override fun onSaveInstanceState(outState: Bundle) {
super.onSaveInstanceState(outState)
outState.putString(LAST_SEARCH_QUERY, latest)
}
private fun search(query: String) {
// Make sure we cancel the previous job before creating a new one
searchJob?.cancel()
searchJob = lifecycleScope.launch {
bookListViewModel.searchRepo(query).collectLatest{
adapter.submitData(it)
}
}
}
private fun initAdapter() {
binding.rvBooks.adapter = adapter.withLoadStateHeaderAndFooter(
header = BooksLoadStateAdapter { adapter.retry() },
footer = BooksLoadStateAdapter { adapter.retry() }
)
adapter.addLoadStateListener { loadState ->
// Only show the list if refresh succeeds.
binding.rvBooks.isVisible = loadState.source.refresh is LoadState.NotLoading
// Show loading spinner during initial load or refresh.
binding.pbLoading.isVisible = loadState.source.refresh is LoadState.Loading
// Show the retry state if initial load or refresh fails.
binding.retryButton.isVisible = loadState.source.refresh is LoadState.Error
// Toast on any error, regardless of whether it came from RemoteMediator or PagingSource
val errorState = loadState.source.append as? LoadState.Error
?: loadState.source.prepend as? LoadState.Error
?: loadState.append as? LoadState.Error
?: loadState.prepend as? LoadState.Error
errorState?.let {
Toast.makeText(
context,
"\uD83D\uDE28 Wooops ${it.error}",
Toast.LENGTH_LONG
).show()
}
}
}
private fun initSearch(menu: Menu) {
val searchItem = menu.findItem(R.id.action_search)
val searchView = searchItem.actionView as android.widget.SearchView
searchView.setOnQueryTextListener(object : SearchView.OnQueryTextListener, android.widget.SearchView.OnQueryTextListener {
override fun onQueryTextSubmit(query: String?): Boolean {
try {
latest = query!!
updateBookListFromInput(query)
} catch (e: Exception) {
Timber.d(e)
}
return false
}
override fun onQueryTextChange(newText: String?): Boolean {
return false
}
})
lifecycleScope.launch {
adapter.loadStateFlow
// Only emit when REFRESH LoadState changes.
.distinctUntilChangedBy { it.refresh }
// Only react to cases where REFRESH completes i.e., NotLoading.
.filter { it.refresh is LoadState.NotLoading }
.collect { binding.rvBooks.scrollToPosition(0) }
}
}
private fun updateBookListFromInput(query: String?) {
query?.trim().let {
if (!it.isNullOrEmpty()) {
search(it.toString())
}
}
}
override fun onCreateOptionsMenu(menu: Menu, inflater: MenuInflater) {
inflater.inflate(R.menu.book_list_menu, menu)
initSearch(menu)
_menu = menu
val recentList: ArrayList<String> = SpUtil.getQueryList(requireContext())
var recentMenu: MenuItem? = null
for (item in recentList) {
recentMenu = menu.add(Menu.NONE, recentList.indexOf(item), Menu.NONE, item)
}
}
companion object {
private const val LAST_SEARCH_QUERY: String = "last_search_query"
private const val DEFAULT_QUERY = "Fishing"
}
}
ダオ:
@Dao
interface BooksDao {
@Insert(onConflict = OnConflictStrategy.REPLACE)
suspend fun insert(books: List<Book>)
@Query("DELETE FROM books")
suspend fun clearBooks()
@Query("SELECT * FROM books WHERE (title LIKE :title) OR (authors LIKE :author) " +
"OR (publisher LIKE :publisher) ORDER BY title ASC")
fun getBooks(title: String, author: String = "", publisher: String = ""): PagingSource<Int, Book>
}
サービス：
interface BookService {
@GET("volumes")
suspend fun searchBooks(
@Query("q") query: String,
@Query("key") apiKey: String,
@Query("maxResults") max: Int,
@Query("startIndex") page: Int
): BookSearchResponse
}
誰かが私が間違っていることを指摘し、この問題を解決するのを手伝ってくれれば素晴らしいことです. ありがとうございました