Android: Paging3: Duplicates items

Question

Problem: I get 40 items at the beginning of the list, then it starts to count from 11, and after this, everything is good. So, 1...40,11,12,13,...,300.

And when I scroll a lot to the bottom and then scroll up to see first items, the items have been changed to 1,2,...,10,1,2,...,10,1,2,...,10,11,12,...,300.

But, when I pass false to enablePlaceholders in the PagingConfig, when I scroll to the bottom, I see the issue as I said above(1,2,..,40,11,...,300) and suddenly the 40 items vanish and I only see 1,2,...,10 + 11,12,...,300(the correct way); And it doesn't change or get worse again.

ProductsPagingSource:

@Singleton
class ProductsPagingSource @Inject constructor(
    private val productsApi: ProductsApi
    //private val query: String
) : RxPagingSource() {

    override fun loadSingle(params: LoadParams): Single> {
        val position = params.key ?: STARTING_PAGE_INDEX
        //val apiQuery = query

        return productsApi.getBeersList(position, params.loadSize)
            .subscribeOn(Schedulers.io())
            .map { listBeerResponse ->
                listBeerResponse.map { beerResponse ->
                    beerResponse.toDomain()
                }
            }
            .map { toLoadResult(it, position) }
            .onErrorReturn { LoadResult.Error(it) }
    }

    private fun toLoadResult(
        @NonNull response: List,
        position: Int
    ): LoadResult {
        return LoadResult.Page(
            data = response,
            prevKey = if (position == STARTING_PAGE_INDEX) null else position - 1,
            nextKey = if (response.isEmpty()) null else position + 1,
            itemsBefore = LoadResult.Page.COUNT_UNDEFINED,
            itemsAfter = LoadResult.Page.COUNT_UNDEFINED
        )
    }

}

ProductsListRepositoryImpl:

@Singleton
class ProductsListRepositoryImpl @Inject constructor(
    private val pagingSource: ProductsPagingSource
) : ProductsListRepository {

    override fun getBeers(ids: String): Flowable> = Pager(
        config = PagingConfig(
            pageSize = 10,
            enablePlaceholders = true,
            maxSize = 30,
            prefetchDistance = 5,
            initialLoadSize = 40
        ),
        pagingSourceFactory = { pagingSource }
    ).flowable

}

ProductsListViewModel:

class ProductsListViewModel @ViewModelInject constructor(
    private val getBeersUseCase: GetBeersUseCase
) : BaseViewModel() {

    private val _ldProductsList: MutableLiveData> = MutableLiveData()
    val ldProductsList: LiveData> = _ldProductsList

    init {
        loading(true)
        getProducts("")
    }

    private fun getProducts(ids: String) {
        loading(false)
        getBeersUseCase(GetBeersParams(ids = ids))
            .cachedIn(viewModelScope)
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe {
                _ldProductsList.value = it
            }.addTo(compositeDisposable)
    }

}

ProductsListFragment:

@AndroidEntryPoint
class ProductsListFragment : Fragment(R.layout.fragment_product_list) {

    private val productsListViewModel: ProductsListViewModel by viewModels()

    private val productsListAdapter: ProductsListAdapter by lazy {
        ProductsListAdapter(::navigateToProductDetail)
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        setupRecycler()
        setupViewModel()
    }

    private fun setupRecycler() {
        itemErrorContainer.gone()
        productListRecyclerView.adapter = productsListAdapter
    }

    private fun setupViewModel() {
        productsListViewModel.run {

            observe(ldProductsList, ::addProductsList)

            observe(ldLoading, ::loadingUI)

            observe(ldFailure, ::handleFailure)

        }
    }

    private fun addProductsList(productsList: PagingData) {
        loadingUI(false)
        productListRecyclerView.visible()
        productsListAdapter.submitData(lifecycle, productsList)
    }
...

BASE_DIFF_CALLBACK:

val BASE_DIFF_CALLBACK = object : DiffUtil.ItemCallback() {

    override fun areItemsTheSame(oldItem: RecyclerItem, newItem: RecyclerItem): Boolean {
        return oldItem.id == newItem.id
    }

    override fun areContentsTheSame(oldItem: RecyclerItem, newItem: RecyclerItem): Boolean {
        return oldItem == newItem
    }

}

BasePagedListAdapter:

abstract class BasePagedListAdapter(
    vararg types: Cell,
    private val onItemClick: (RecyclerItem, ImageView) -> Unit
) : PagingDataAdapter(BASE_DIFF_CALLBACK) {

    private val cellTypes: CellTypes = CellTypes(*types)

    override fun getItemViewType(position: Int): Int {
        getItem(position).let {
            return cellTypes.of(it).type()
        }
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {
        return cellTypes.of(viewType).holder(parent)
    }

    override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
        getItem(position).let {
            cellTypes.of(it).bind(holder, it, onItemClick)
        }
    }

}

Dr.jacky · Accepted Answer

I had to set the same number for pageSize and initialLoadSize. Also, I had to set the enablePlaceholders to false.

config = PagingConfig(
            pageSize = 10,
            enablePlaceholders = false,
            maxSize = 30,
            prefetchDistance = 5,
            initialLoadSize = 10
        ),

But still, I want to know if it's the normal way? If yes, I couldn't find anywhere point to this! If not, why's that? Why initialLoadSize can not have value more than the pageSize?! As we can see, the default value for the initialLoadSize is:

internal const val DEFAULT_INITIAL_PAGE_MULTIPLIER = 3
val initialLoadSize: Int = pageSize * DEFAULT_INITIAL_PAGE_MULTIPLIER,

Android: Paging3: Duplicates items

Answers (2)

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