PagingDataAdapter

public abstract class PagingDataAdapter<T extends Object, VH extends RecyclerView.ViewHolder> extends RecyclerView.Adapter


RecyclerView.Adapter base class for presenting paged data from PagingDatas in a RecyclerView.

This class is a convenience wrapper around AsyncPagingDataDiffer that implements common default behavior for item counting, and listening to update events.

To present a Pager, use collectLatest to observe Pager.flow and call submitData whenever a new PagingData is emitted.

If using RxJava and LiveData extensions on Pager, use the non-suspending overload of submitData, which accepts a Lifecycle.

PagingDataAdapter listens to internal PagingData loading events as pages are loaded, and uses DiffUtil on a background thread to compute fine grained updates as updated content in the form of new PagingData objects are received.

State Restoration: To be able to restore RecyclerView state (e.g. scroll position) after a configuration change / application recreate, PagingDataAdapter calls RecyclerView.Adapter.setStateRestorationPolicy with RecyclerView.Adapter.StateRestorationPolicy.PREVENT upon initialization and waits for the first page to load before allowing state restoration. Any other call to RecyclerView.Adapter.setStateRestorationPolicy by the application will disable this logic and will rely on the user set value.

val USER_COMPARATOR = object : DiffUtil.ItemCallback<User>() {
    override fun areItemsTheSame(oldItem: User, newItem: User): Boolean =
        // User ID serves as unique ID
        oldItem.userId == newItem.userId

    override fun areContentsTheSame(oldItem: User, newItem: User): Boolean =
        // Compare full contents (note: Java users should call .equals())
        oldItem == newItem
}

class UserAdapter : PagingDataAdapter<User, UserViewHolder>(USER_COMPARATOR) {
    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): UserViewHolder {
        return UserViewHolder.create(parent)
    }

    override fun onBindViewHolder(holder: UserViewHolder, position: Int) {
        val repoItem = getItem(position)
        // Note that item may be null, ViewHolder must support binding null item as placeholder
        holder.bind(repoItem)
    }
}

Summary

Public fields

final @NonNull Flow<@NonNull CombinedLoadStates>

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

final @NonNull 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.

Public constructors

<T extends Object, VH extends RecyclerView.ViewHolder> PagingDataAdapter(
    @NonNull DiffUtil.ItemCallback<@NonNull T> diffCallback,
    @NonNull CoroutineDispatcher mainDispatcher,
    @NonNull CoroutineDispatcher workerDispatcher
)

Public methods

final void
addLoadStateListener(
    @NonNull Function1<@NonNull CombinedLoadStatesUnit> listener
)

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

final void
addOnPagesUpdatedListener(@NonNull Function0<Unit> listener)

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

int

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

final long
getItemId(int position)

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

final @Nullable T
peek(@IntRange(from = 0) int index)

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

final void

Refresh the data presented by this PagingDataAdapter.

final void

Remove a previously registered CombinedLoadStates listener.

final void

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

final void

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

final void
setHasStableIds(boolean hasStableIds)

Stable ids are unsupported by PagingDataAdapter.

void

Sets the state restoration strategy for the Adapter.

final @NonNull ItemSnapshotList<@NonNull T>

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

final void

Present a