PagingDataAdapter

fun addLoadStateListener(listener: (CombinedLoadStates) -> Unit): Unit

Add a CombinedLoadStates listener to observe the loading state of the current PagingData.

As new PagingData generations are submitted and displayed, the listener will be notified to reflect the current CombinedLoadStates.

import androidx.paging.LoadState

val adapter = UserPagingAdapter()
adapter.addLoadStateListener {
    // show a retry button outside the list when refresh hits an error
    retryButton.isVisible = it.refresh is LoadState.Error

    // swipeRefreshLayout displays whether refresh is occurring
    swipeRefreshLayout.isRefreshing = it.refresh is LoadState.Loading

    // show an empty state over the list when loading initially, before items are loaded
    emptyState.isVisible = it.refresh is LoadState.Loading && adapter.itemCount == 0
}

fun addOnPagesUpdatedListener(listener: () -> Unit): Unit

Add a listener which triggers after the pages presented to the UI are updated, even if the actual items presented don't change.

An update is triggered from one of the following:

• submitData is called and initial load completes, regardless of any differences in the loaded data

• A Page is inserted

• A Page is dropped

open fun getItemCount(): Int

Returns the total number of items in the data set held by the adapter.

final fun getItemId(position: Int): Long

Note: getItemId is final, because stable IDs are unnecessary and therefore unsupported.

PagingDataAdapter's async diffing means that efficient change animations are handled for you, without the performance drawbacks of RecyclerView.Adapter.notifyDataSetChanged. Instead, the diffCallback parameter of the PagingDataAdapter serves the same functionality - informing the adapter and RecyclerView how items are changed and moved.

@MainThread
fun peek(index: @IntRange(from = 0) Int): T?

Returns the presented item at the specified position, without notifying Paging of the item access that would normally trigger page loads.

fun refresh(): Unit

Refresh the data presented by this PagingDataAdapter.

refresh triggers the creation of a new PagingData with a new instance of PagingSource to represent an updated snapshot of the backing dataset. If a RemoteMediator is set, calling refresh will also trigger a call to RemoteMediator.load with LoadType to allow RemoteMediator to check for updates to the dataset backing PagingSource.

Note: This API is intended for UI-driven refresh signals, such as swipe-to-refresh. Invalidation due repository-layer signals, such as DB-updates, should instead use PagingSource.invalidate.

import androidx.appcompat.app.AppCompatActivity
import androidx.paging.LoadState

class MyActivity : AppCompatActivity() {
    private lateinit var binding: MyActivityBinding
    private val pagingAdapter = UserPagingAdapter()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = MyActivityBinding.inflate(layoutInflater)
        setContentView(binding.root)

        binding.recyclerView.adapter = pagingAdapter
        pagingAdapter.addLoadStateListener { loadStates ->
            binding.swipeRefreshLayout.isRefreshing = loadStates.refresh is LoadState.Loading
        }

        binding.swipeRefreshLayout.setOnRefreshListener { pagingAdapter.refresh() }
    }
}

fun removeLoadStateListener(listener: (CombinedLoadStates) -> Unit): Unit

Remove a previously registered CombinedLoadStates listener.

fun removeOnPagesUpdatedListener(listener: () -> Unit): Unit

Remove a previously registered listener for new PagingData generations completing initial load and presenting to the UI.

fun retry(): Unit

Retry any failed load requests that would result in a LoadState.Error update to this PagingDataAdapter.

Unlike refresh, this does not invalidate PagingSource, it only retries failed loads within the same generation of PagingData.

LoadState.Error can be generated from two types of load requests:

• PagingSource.load returning PagingSource.LoadResult.Error

• RemoteMediator.load returning RemoteMediator.MediatorResult.Error

final fun setHasStableIds(hasStableIds: Boolean): Unit

Stable ids are unsupported by PagingDataAdapter. Calling this method is an error and will result in an UnsupportedOperationException.

open fun setStateRestorationPolicy(
    strategy: RecyclerView.Adapter.StateRestorationPolicy
): Unit

Sets the state restoration strategy for the Adapter. By default, it is set to ALLOW which means RecyclerView expects any set Adapter to be immediately capable of restoring the RecyclerView's saved scroll position.

This behaviour might be undesired if the Adapter's data is loaded asynchronously, and thus unavailable during initial layout (e.g. after Activity rotation). To avoid losing scroll position, you can change this to be either PREVENT_WHEN_EMPTY or PREVENT. Note that the former means your RecyclerView will restore state as soon as Adapter has 1 or more items while the latter requires you to call setStateRestorationPolicy with either ALLOW or PREVENT_WHEN_EMPTY again when the Adapter is ready to restore its state.

RecyclerView will still layout even when State restoration is disabled. The behavior of how State is restored is up to the LayoutManager. All default LayoutManagers will override current state with restored state when state restoration happens (unless an explicit call to scrollToPosition is made).

Calling this method after state is restored will not have any effect other than changing the return value of getStateRestorationPolicy.

fun snapshot(): ItemSnapshotList<T>

Returns a new ItemSnapshotList representing the currently presented items, including any placeholders if they are enabled.

suspend fun submitData(pagingData: PagingData<T>): Unit

Present a PagingData until it is invalidated by a call to refresh or PagingSource.invalidate.

This method is typically used when collecting from a Flow produced by Pager. For RxJava or LiveData support, use the non-suspending overload of submitData, which accepts a Lifecycle.

Note: This method suspends while it is actively presenting page loads from a PagingData, until the PagingData is invalidated. Although cancellation will propagate to this call automatically, collecting from a Pager.flow with the intention of presenting the most up-to-date representation of your backing dataset should typically be done using collectLatest.

import androidx.activity.viewModels
import androidx.appcompat.app.AppCompatActivity
import androidx.lifecycle.lifecycleScope

class MyFlowActivity : AppCompatActivity() {
    val pagingAdapter = UserPagingAdapter()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        val viewModel by viewModels<UserListViewModel>()

        lifecycleScope.launch {
            viewModel.pagingFlow.collectLatest { pagingData ->
                // submitData suspends until loading this generation of data stops
                // so be sure to use collectLatest {} when presenting a Flow<PagingData>
                pagingAdapter.submitData(pagingData)
            }
        }
    }
}

fun submitData(lifecycle: Lifecycle, pagingData: PagingData<T>): Unit

Present a PagingData until it is either invalidated or another call to submitData is made.

This method is typically used when observing a RxJava or LiveData stream produced by Pager. For Flow support, use the suspending overload of submitData, which automates cancellation via CoroutineScope instead of relying of Lifecycle.

import androidx.activity.viewModels
import androidx.appcompat.app.AppCompatActivity

class MyLiveDataActivity : AppCompatActivity() {
    val pagingAdapter = UserPagingAdapter()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        val viewModel by viewModels<UserListViewModel>()

        viewModel.pagingLiveData.observe(this) { pagingData ->
            pagingAdapter.submitData(lifecycle, pagingData)
        }
    }
}

import androidx.activity.viewModels
import androidx.appcompat.app.AppCompatActivity

class MyRxJava2Activity : AppCompatActivity() {
    val pagingAdapter = UserPagingAdapter()
    val disposable = CompositeDisposable()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        val viewModel by viewModels<UserListViewModel>()

        viewModel.pagingFlowable
            .autoDispose(this) // Using AutoDispose to handle subscription lifecycle
            .subscribe { pagingData -> pagingAdapter.submitData(lifecycle, pagingData) }
    }
}

fun withLoadStateFooter(footer: LoadStateAdapter<*>): ConcatAdapter

Create a ConcatAdapter with the provided LoadStateAdapters displaying the LoadType.APPEND as a list item at the start of the presented list.

fun withLoadStateHeader(header: LoadStateAdapter<*>): ConcatAdapter

Create a ConcatAdapter with the provided LoadStateAdapters displaying the LoadType.PREPEND as a list item at the end of the presented list.

fun withLoadStateHeaderAndFooter(
    header: LoadStateAdapter<*>,
    footer: LoadStateAdapter<*>
): ConcatAdapter

Create a ConcatAdapter with the provided LoadStateAdapters displaying the LoadType.PREPEND and LoadType.APPENDs as list items at the start and end respectively.

@MainThread
protected fun getItem(position: @IntRange(from = 0) Int): T?

Returns the presented item at the specified position, notifying Paging of the item access to trigger any loads necessary to fulfill prefetchDistance.

val loadStateFlow: Flow<CombinedLoadStates>

A hot Flow of CombinedLoadStates that emits a snapshot whenever the loading state of the current PagingData changes.

This flow is conflated, so it buffers the last update to CombinedLoadStates and immediately delivers the current load states on collection.

val onPagesUpdatedFlow: Flow<Unit>

A hot Flow that emits after the pages presented to the UI are updated, even if the actual items presented don't change.

An update is triggered from one of the following:

• submitData is called and initial load completes, regardless of any differences in the loaded data

• A Page is inserted

• A Page is dropped

Note: This is a SharedFlow configured to replay 0 items with a buffer of size 64. If a collector lags behind page updates, it may trigger multiple times for each intermediate update that was presented while your collector was still working. To avoid this behavior, you can conflate this Flow so that you only receive the latest update, which is useful in cases where you are simply updating UI and don't care about tracking the exact number of page updates.