标签: android-paging

我刚刚查看了分页库，发现BoundaryCallback有三个方法。对于名为onItemAtFrontLoaded()的方法之一，文档说

Called when the item at the front of the PagedList has been loaded, and access has occurred within prefetchDistance of it.

我不太确定什么时候会调用这个方法，有人可以给我一个详细的例子吗？

我已将页面大小设置为 10，观察者中的页面大小给出了正确的大小，但数据库（ROOM）中的所有项目都已加载到视图持有者中

边界回调onItemAtEndLoaded正在使用数据库中的最后一个项目进行调用。

这是我的配置：

public LiveData<PagedList<Design>> getDesignList(List<String> types, String idCode){
    DataSource.Factory<Integer, Design> factory = mRepository.getDesigns(types, idCode);
    PagedList.Config pagedListConfig =
            (new PagedList.Config.Builder())
                    .setEnablePlaceholders(false)
                    .setInitialLoadSizeHint(10)
                    .setPageSize(10)
                    .build();
    return new LivePagedListBuilder<>(factory, pagedListConfig)
            .setBoundaryCallback(**boundCallBack**)
            .setFetchExecutor(mRepository.mIoExecutor)
            .build();
}

存储库（mRepository.getDesigns）：

public DataSource.Factory<Integer, Design> getDesigns(List<String> types, String idCode) {
    return designDao.getDesigns(types,idCode);
}

Dao:(获取设计)

@Query("SELECT * FROM Design WHERE design_type IN (:types) AND id=:idCode ORDER BY design_id ASC")
DataSource.Factory<Integer, Design> getDesigns(List<String> types, String idCode);

边界回调（boundCallBack）：

public class BoundCall extends …

使用paging 3.0，我成功地实现了它。现在我想为其添加搜索功能。

我只是显示照片库以及分页功能。现在我想在有人搜索时使分页无效

但每当我在搜索上调用无效时。应用程序崩溃..

照片片段.kt

@AndroidEntryPoint
class PhotosFragment : BaseFragment<FragmentPhotosBinding,PhotosFragmentViewModel>(R.layout.fragment_photos),
    SearchView.OnQueryTextListener, LifecycleObserver {
    override val mViewModel: PhotosFragmentViewModel by viewModels()

    private lateinit var photoAdapter: PhotoCollectionAdapter

    override fun onAttach(context: Context) {
        super.onAttach(context)
        activity?.lifecycle?.addObserver(this)
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        setHasOptionsMenu(true)
        ///mViewModel.setFilter(getString(R.string.search_filter_default_value))
        initAdapter()
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
    fun onCreated(){
        mViewModel.trendingPhotos.observe(viewLifecycleOwner, Observer {
            photoAdapter.submitData(lifecycle,it)
        })
    }

    private fun initAdapter() {
        photoAdapter = PhotoCollectionAdapter()
        photoAdapter.stateRestorationPolicy = RecyclerView.Adapter.StateRestorationPolicy.PREVENT_WHEN_EMPTY

        mBinding.recyclerView.apply {
            layoutManager = LinearLayoutManager(context)
            setHasFixedSize(true)
            adapter = photoAdapter
        }

        photoAdapter.addLoadStateListener { loadState -> …

从自定义分页实现迁移到Jetpack Paging 3 库后，数据未按预期加载。根据以下内容正确处理第一页：PagingConfigPager

internal fun createProductListPager(pagingSource: ProductListPagingSource): Pager<Int, Product> = Pager(
    config = PagingConfig(
        pageSize = 10,
        prefetchDistance = 2,
    ),
    initialKey = 0,
) { pagingSource }

以下是摘录Adapter：

public class PagingProductCardAdapter(private val viewBinder: CoreViewBinder) :
    PagingDataAdapter<Listable, RecyclerView.ViewHolder>(viewBinder.getDiffUtils()) {


    public val list: List<Listable>
        get() = snapshot().items


    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {
      // ...
    }

    override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
        viewBinder.bind(list[position], holder)
    }
    // ...
}

当滚动到 …

我正在使用该Paging 3库，LazyColumn并且我想根据购物清单项目的类别对列表进行排序。在下面的代码中，LazyColumn抱怨它正在期待LazyPagingItems<TypeVariable(T)>该items属性，但发现了List<ShoppingListItem?>。我怎样才能解决这个问题？

可组合的

val lazyListState = rememberLazyListState()
val successItems = allItemsState.allItems?.collectAsLazyPagingItems()

LazyColumn(
    state = lazyListState,
    modifier = Modifier
        .fillMaxWidth(),
    contentPadding = PaddingValues(
        start = 5.dp,
        end = 5.dp,
        top = 8.dp,
        bottom = 165.dp
    ),
    verticalArrangement = Arrangement.spacedBy(5.dp),
) {
    val groupedByCategory = successItems!!.itemSnapshotList.groupBy { it!!.category }

    groupedByCategory.forEach { (initial, shoppingListItems) ->
        item {
            Text(text = initial)
        }
        items(
            items = shoppingListItems, //Throws error at this line
            key …

我有一个 RecyclerView 与 Paging 一起实现，用于从房间数据库加载列表。当尺寸较小时，列表工作正常。当大小达到 50 - 60 左右时，列表仍然可以正常工作，但是当我切换到另一个片段然后返回到列表时，它会阻塞 UI 大约 1.5 - 2 秒，这在用户体验中非常沉闷（参见下面的 GIF） ）：

我的代码如下：

DAO

@Query("SELECT * FROM account_table WHERE userID = :userID")
fun getAll(userID: String): DataSource.Factory<Int, Account>

存储库

class AccountRepository private constructor(application: Application) {

private val database =
    LockyDatabase.getDatabase(
        application
    )
private val accountDao = database.accountDao()

companion object {
    @Volatile
    private var instance: AccountRepository? = null

    fun getInstance(application: Application) =
        instance ?: synchronized(this) {
            instance ?: AccountRepository(application).also { instance = it }
        }
}

fun …

我正在使用 Android 分页库，如下所述：https : //developer.android.com/topic/libraries/architecture/paging.html

但我也有一个 EditText 用于按名称搜索国家/地区。

如何过滤 Paging 库中的结果以仅显示匹配的国家/地区？

public final LiveData> countriesPagedList;

public AllCountriesViewModel(@NonNull Application application) {
    super(application);
    appRepository = new AppRepository(application);


PagedList.Config config = new PagedList.Config.Builder()
        .setEnablePlaceholders(true)
        .setPageSize(30)
        .setInitialLoadSizeHint(10)
        .setPrefetchDistance(50)
        .build();

    countriesPagedList = new LivePagedListBuilder(appRepository.getAllCountries(),config).build();
}