PagedListAdapter

Added in 2.0.0
Deprecated in 3.0.0

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


RecyclerView.Adapter base class for presenting paged data from androidx.paging.PagedLists in a RecyclerView.

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

While using a LiveData is an easy way to provide data to the adapter, it isn't required - you can use submitList when new lists are available.

PagedListAdapter listens to PagedList loading callbacks as pages are loaded, and uses DiffUtil on a background thread to compute fine grained updates as new PagedLists are received.

Handles both the internal paging of the list as more data is loaded, and updates in the form of new PagedLists.

A complete usage pattern with Room would look like this:

@Dao
interface UserDao {
@Query("SELECT * FROM user ORDER BY lastName ASC")
public abstract DataSource.Factory<Integer, User> usersByLastName();
}

class MyViewModel extends ViewModel {
public final LiveData<PagedList<User>> usersList;
public MyViewModel(UserDao userDao) {
usersList = new LivePagedListBuilder&lt;>(
userDao.usersByLastName(), /* page size */20).build();
}
}

class MyActivity extends AppCompatActivity {
@Override
public void onCreate(Bundle savedState) {
super.onCreate(savedState);
MyViewModel viewModel = new ViewModelProvider(this).get(MyViewModel.class);
RecyclerView recyclerView = findViewById(R.id.user_list);
UserAdapter&lt;User> adapter = new UserAdapter();
viewModel.usersList.observe(this, pagedList -> adapter.submitList(pagedList));
recyclerView.setAdapter(adapter);
}
}

class UserAdapter extends PagedListAdapter<User, UserViewHolder> {
public UserAdapter() {
super(DIFF_CALLBACK);
}
@Override
public void onBindViewHolder(UserViewHolder holder, int position) {
User user = getItem(position);
if (user != null) {
holder.bindTo(user);
} else {
// Null defines a placeholder item - PagedListAdapter will automatically invalidate
// this row when the actual object is loaded from the database
holder.clear();
}
}
public static final DiffUtil.ItemCallback&lt;User> DIFF_CALLBACK =
new DiffUtil.ItemCallback<User>() {
@Override
public boolean areItemsTheSame(@NonNull User oldUser, @NonNull User newUser) {
// User properties may have changed if reloaded from the DB, but ID is fixed
return oldUser.getId() == newUser.getId();
}
@Override
public boolean areContentsTheSame(@NonNull User oldUser, @NonNull User newUser) {
// NOTE: if you use equals, your object must properly override Object#equals()
// Incorrectly returning false here will result in too many animations.
return oldUser.equals(newUser);
}
}
}

Advanced users that wish for more control over adapter behavior, or to provide a specific base class should refer to AsyncPagedListDiffer, which provides the mapping from paging events to adapter-friendly callbacks.

Parameters
<T extends Object>

Type of the PagedLists this Adapter will receive.

<VH extends RecyclerView.ViewHolder>

A class that extends ViewHolder that will be used by the adapter.

Summary

Protected constructors

<T extends Object, VH extends RecyclerView.ViewHolder> PagedListAdapter(
    @NonNull AsyncDifferConfig<@NonNull T> config
)
<T extends Object, VH extends RecyclerView.ViewHolder> PagedListAdapter(
    @NonNull DiffUtil.ItemCallback<@NonNull T> diffCallback
)

Creates a PagedListAdapter with default threading and androidx.recyclerview.widget.ListUpdateCallback.

Public methods

void
addLoadStateListener(
    @NonNull Function2<@NonNull LoadType, @NonNull LoadStateUnit> listener
)

Add a LoadState listener to observe the loading state of the current PagedList.

PagedList<@NonNull T>

Returns the PagedList currently being displayed by the PagedListAdapter.

int

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

void

This method is deprecated. Use the two argument variant instead.

void
onCurrentListChanged(
    PagedList<@NonNull T> previousList,
    PagedList<@NonNull T> currentList
)

Called when the current PagedList is updated.

void

Remove a previously registered LoadState listener.

void
submitList(PagedList<@NonNull T> pagedList)

Set the new list to be displayed.

void
submitList(PagedList<@NonNull T> pagedList, Runnable commitCallback)

Set the new list to be displayed.

final @NonNull ConcatAdapter

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

final @NonNull ConcatAdapter

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

final @NonNull ConcatAdapter

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

Protected methods

T
getItem(int position)

Inherited methods

From androidx.recyclerview.widget.RecyclerView.Adapter
final void
bindViewHolder(@NonNull VH holder, int position)

This method internally calls onBindViewHolder to update the ViewHolder contents with the item at the given position and also sets up some private fields to be used by RecyclerView.

final @NonNull VH
createViewHolder(@NonNull ViewGroup parent, int viewType)

This method calls onCreateViewHolder to create a new ViewHolder and initializes some private fields to be used by RecyclerView.

int

Returns the position of the given ViewHolder in the given Adapter.

long
getItemId(int position)

Return the stable ID for the item at position.

int
getItemViewType(int position)

Return the view type of the item at position for the purposes of view recycling.

final @NonNull RecyclerView.Adapter.StateRestorationPolicy

Returns when this Adapter wants to restore the state.

final boolean

Returns true if one or more observers are attached to this adapter.

final boolean

Returns true if this adapter publishes a unique long value that can act as a key for the item at a given position in the data set.

final void

Notify any registered observers that the data set has changed.

final void
notifyItemChanged(int position)

Notify any registered observers that the item at position has changed.

final void
notifyItemChanged(int position, @Nullable Object payload)

Notify any registered observers that the item at position has changed with an optional payload object.

final void
notifyItemInserted(int position)

Notify any registered observers that the item reflected at position has been newly inserted.

final void
notifyItemMoved(int fromPosition, int toPosition)

Notify any registered observers that the item reflected at fromPosition has been moved to toPosition.

final void
notifyItemRangeChanged(int positionStart, int itemCount)

Notify any registered observers that the itemCount items starting at position positionStart have changed.

final void
notifyItemRangeChanged(
    int positionStart,
    int itemCount,
    @Nullable Object payload
)

Notify any registered observers that the itemCount items starting at position positionStart have changed.

final void
notifyItemRangeInserted(int positionStart, int itemCount)

Notify any registered observers that the currently reflected itemCount items starting at positionStart have been newly inserted.

final void
notifyItemRangeRemoved(int positionStart, int itemCount)

Notify any registered observers that the itemCount items previously located at positionStart have been removed from the data set.

final void
notifyItemRemoved(int position)

Notify any registered observers that the item previously located at position has been removed from the data set.

void

Called by RecyclerView when it starts observing this Adapter.

abstract void
onBindViewHolder(@NonNull VH holder, int position)

Called by RecyclerView to display the data at the specified position.

void
onBindViewHolder(
    @NonNull VH holder,
    int position,
    @NonNull List<@NonNull Object> payloads
)

Called by RecyclerView to display the data at the specified position.

abstract @NonNull VH
onCreateViewHolder(@NonNull ViewGroup parent, int viewType)

Called when RecyclerView needs a new ViewHolder of the given type to represent an item.

void

Called by RecyclerView when it stops observing this Adapter.

boolean

Called by the RecyclerView if a ViewHolder created by this Adapter cannot be recycled due to its transient state.

void

Called when a view created by this adapter has been attached to a window.

void

Called when a view created by this adapter has been detached from its window.

void
onViewRecycled(@NonNull VH holder)

Called when a view created by this adapter has been recycled.

void

Register a new observer to listen for data changes.

void
setHasStableIds(boolean hasStableIds)

Indicates whether each item in the data set can be represented with a unique identifier of type java.lang.Long.

void

Sets the state restoration strategy for the Adapter.

void

Unregister an observer currently listening for data changes.

Protected constructors

PagedListAdapter

protected <T extends Object, VH extends RecyclerView.ViewHolder> PagedListAdapter(
    @NonNull AsyncDifferConfig<@NonNull T> config
)

PagedListAdapter

protected <T extends Object, VH extends RecyclerView.ViewHolder> PagedListAdapter(
    @NonNull DiffUtil.ItemCallback<@NonNull T> diffCallback
)

Creates a PagedListAdapter with default threading and androidx.recyclerview.widget.ListUpdateCallback.

Convenience for PagedListAdapter, which uses default threading behavior.

Parameters
@NonNull DiffUtil.ItemCallback<@NonNull T> diffCallback

The DiffUtil.ItemCallback instance to compare items in the list.

Public methods

addLoadStateListener

Added in 3.0.0
Deprecated in 3.0.0
public void addLoadStateListener(
    @NonNull Function2<@NonNull LoadType, @NonNull LoadStateUnit> listener
)

Add a LoadState listener to observe the loading state of the current PagedList.

As new PagedLists are submitted and displayed, the listener will be notified to reflect current LoadType.REFRESH, LoadType.PREPEND, and LoadType.APPEND states.

Parameters
@NonNull Function2<@NonNull LoadType, @NonNull LoadStateUnit> listener

Listener to receive LoadState updates.

getCurrentList

Added in 2.0.0
Deprecated in 3.0.0
public PagedList<@NonNull T> getCurrentList()

Returns the PagedList currently being displayed by the PagedListAdapter.

This is not necessarily the most recent list passed to submitList, because a diff is computed asynchronously between the new list and the current list before updating the currentList value. May be null if no PagedList is being presented.

Returns
PagedList<@NonNull T>

The list currently being displayed.

getItemCount

Added in 2.0.0
Deprecated in 3.0.0
public int getItemCount()

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

Returns
int

The total number of items in this adapter.

onCurrentListChanged

Added in 2.0.0
Deprecated in 2.1.0
public void onCurrentListChanged(PagedList<@NonNull T> currentList)

Called when the current PagedList is updated.

This may be dispatched as part of submitList if a background diff isn't needed (such as when the first list is passed, or the list is cleared). In either case, PagedListAdapter will simply call notifyItemRangeInserted/Removed(0, mPreviousSize).

This method will notbe called when the Adapter switches from presenting a PagedList to a snapshot version of the PagedList during a diff. This means you cannot observe each PagedList via this method.

Parameters
PagedList<@NonNull T> currentList

new PagedList being displayed, may be null.

onCurrentListChanged

Added in 2.1.0
Deprecated in 3.0.0
public void onCurrentListChanged(
    PagedList<@NonNull T> previousList,
    PagedList<@NonNull T> currentList
)

Called when the current PagedList is updated.

This may be dispatched as part of submitList if a background diff isn't needed (such as when the first list is passed, or the list is cleared). In either case, PagedListAdapter will simply call notifyItemRangeInserted/Removed(0, mPreviousSize).

This method will notbe called when the Adapter switches from presenting a PagedList to a snapshot version of the PagedList during a diff. This means you cannot observe each PagedList via this method.

Parameters
PagedList<@NonNull T> previousList

PagedList that was previously displayed, may be null.

PagedList<@NonNull T> currentList

new PagedList being displayed, may be null.

removeLoadStateListener

Added in 3.0.0
Deprecated in 3.0.0
public void removeLoadStateListener(
    @NonNull Function2<@NonNull LoadType, @NonNull LoadStateUnit> listener
)

Remove a previously registered LoadState listener.

Parameters
@NonNull Function2<@NonNull LoadType, @NonNull LoadStateUnit> listener

Previously registered listener.

submitList

Added in 2.0.0
Deprecated in 3.0.0
public void submitList(PagedList<@NonNull T> pagedList)

Set the new list to be displayed.

If a list is already being displayed, a diff will be computed on a background thread, which will dispatch Adapter.notifyItem events on the main thread.

Parameters
PagedList<@NonNull T> pagedList

The new list to be displayed.

submitList

Added in 2.1.0
Deprecated in 3.0.0
public void submitList(PagedList<@NonNull T> pagedList, Runnable commitCallback)

Set the new list to be displayed.

If a list is already being displayed, a diff will be computed on a background thread, which will dispatch Adapter.notifyItem events on the main thread.

The commit callback can be used to know when the PagedList is committed, but note that it may not be executed. If PagedList B is submitted immediately after PagedList A, and is committed directly, the callback associated with PagedList A will not be run.

Parameters
PagedList<@NonNull T> pagedList

The new list to be displayed.

Runnable commitCallback

Optional runnable that is executed when the PagedList is committed, if it is committed.

withLoadStateFooter

Added in 3.0.0
Deprecated in 3.0.0
public final @NonNull ConcatAdapter withLoadStateFooter(@NonNull LoadStateAdapter<@NonNull ?> footer)

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

withLoadStateHeader

Added in 3.0.0
Deprecated in 3.0.0
public final @NonNull ConcatAdapter withLoadStateHeader(@NonNull LoadStateAdapter<@NonNull ?> header)

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

withLoadStateHeaderAndFooter

Added in 3.0.0
Deprecated in 3.0.0
public final @NonNull ConcatAdapter withLoadStateHeaderAndFooter(
    @NonNull LoadStateAdapter<@NonNull ?> header,
    @NonNull LoadStateAdapter<@NonNull ?> footer
)

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

Protected methods

getItem

Added in 2.0.0
Deprecated in 3.0.0
protected T getItem(int position)