{% setvar book_path %}/reference/androidx/_book.yaml{% endsetvar %} {% include "_shared/_reference-head-tags.html" %}
public abstract class PagedListAdapter<T extends Object, VH extends Object>
RecyclerView.Adapter base class for presenting paged data from androidx.paging.PagedList
s 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 LiveDatasubmitList
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<>(
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<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<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 Object> |
A class that extends ViewHolder that will be used by the adapter. |
Public fields |
|
---|---|
@Nullable PagedList<@NonNull T> |
Returns the |
Public methods |
|
---|---|
void |
Add a |
int |
|
void |
This method is deprecated. Use the two argument variant instead. |
void |
onCurrentListChanged( Called when the current PagedList is updated. |
void |
Remove a previously registered |
void |
submitList(@Nullable PagedList<@NonNull T> pagedList) Set the new list to be displayed. |
void |
Set the new list to be displayed. |
final @NonNull <ERROR CLASS> |
withLoadStateFooter(@NonNull LoadStateAdapter<@NonNull ?> footer) Create a ConcatAdapter with the provided |
final @NonNull <ERROR CLASS> |
withLoadStateHeader(@NonNull LoadStateAdapter<@NonNull ?> header) Create a ConcatAdapter with the provided |
final @NonNull <ERROR CLASS> |
withLoadStateHeaderAndFooter( Create a ConcatAdapter with the provided |
@Nullable
public @Nullable PagedList<@NonNull T> currentList
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.
See also | |
---|---|
onCurrentListChanged |
@NonNull
public void addLoadStateListener(
@NonNull Function2<@NonNull LoadType, @NonNull LoadState, Unit> 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 LoadState, Unit> listener |
Listener to receive |
See also | |
---|---|
removeLoadStateListener |
@NonNull
public voidonCurrentListChanged(@Nullable 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.
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.
See also | |
---|---|
onCurrentListChanged |
@NonNull
public void onCurrentListChanged(
@Nullable PagedList<@NonNull T> previousList,
@Nullable 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.
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 | |
---|---|
@Nullable PagedList<@NonNull T> previousList |
|
@Nullable PagedList<@NonNull T> currentList |
new |
See also | |
---|---|
onCurrentListChanged |
@NonNull
public void removeLoadStateListener(
@NonNull Function2<@NonNull LoadType, @NonNull LoadState, Unit> listener
)
Remove a previously registered LoadState
listener.
Parameters | |
---|---|
@NonNull Function2<@NonNull LoadType, @NonNull LoadState, Unit> listener |
Previously registered listener. |
See also | |
---|---|
addLoadStateListener |
@NonNull
public void submitList(@Nullable 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.
@NonNull
public void submitList(
@Nullable PagedList<@NonNull T> pagedList,
@Nullable 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.
@NonNull
public final <ERROR CLASS> withLoadStateFooter(@NonNull LoadStateAdapter<@NonNull ?> footer)
Create a ConcatAdapter with the provided LoadStateAdapter
s displaying the LoadType.APPEND
as a list item at the start of the presented list.
@NonNull
public final <ERROR CLASS> withLoadStateHeader(@NonNull LoadStateAdapter<@NonNull ?> header)
Create a ConcatAdapter with the provided LoadStateAdapter
s displaying the LoadType.PREPEND
as a list item at the end of the presented list.
@NonNull
public final <ERROR CLASS> withLoadStateHeaderAndFooter(
@NonNull LoadStateAdapter<@NonNull ?> header,
@NonNull LoadStateAdapter<@NonNull ?> footer
)
Create a ConcatAdapter with the provided LoadStateAdapter
s displaying the LoadType.PREPEND
and LoadType.APPEND
s as list items at the start and end respectively.