AsyncPagedListDiffer
public class AsyncPagedListDiffer<T extends Object>
Helper object for mapping a androidx.paging.PagedList into a RecyclerView.Adapter.
For simplicity, the PagedListAdapter wrapper class can often be used instead of the differ directly. This diff class is exposed for complex cases, and where overriding an adapter base class to support paging isn't convenient.
When consuming a LiveData of PagedList, you can observe updates and dispatch them directly to submitList. The AsyncPagedListDiffer then can present this updating data set simply for an adapter. It listens to PagedList loading callbacks, and uses DiffUtil on a background thread to compute updates as new PagedLists are received.
It provides a simple list-like API with getItem and itemCount for an adapter to acquire and present data objects.
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);
final UserAdapter adapter = new UserAdapter();
viewModel.usersList.observe(this, pagedList -> adapter.submitList(pagedList));
recyclerView.setAdapter(adapter);
}
}
class UserAdapter extends RecyclerView.Adapter<UserViewHolder> {
private final AsyncPagedListDiffer<User> differ =
new AsyncPagedListDiffer(this, DIFF_CALLBACK);
@Override
public int getItemCount() {
return differ.getItemCount();
}
public void submitList(PagedList<User> pagedList) {
differ.submitList(pagedList);
}
@Override
public void onBindViewHolder(UserViewHolder holder, int position) {
User user = differ.getItem(position);
if (user != null) {
holder.bindTo(user);
} else {
// Null defines a placeholder item - AsyncPagedListDiffer 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);
}
}
}
| Parameters | |
|---|---|
<T extends Object> |
Type of the PagedLists this differ will receive. |
Summary
Nested types |
|---|
public interface AsyncPagedListDiffer.PagedListListener<T extends Object>This interface is deprecated. PagedList is deprecated and has been replaced by PagingData |
Public constructors |
|---|
<T extends Object> This method is deprecated. PagedList is deprecated and has been replaced by PagingData |
<T extends Object> This method is deprecated. PagedList is deprecated and has been replaced by PagingData |
Public methods |
|
|---|---|
void |
Add a |
final void |
addPagedListListener(Add a callback to receive updates when the current |
void |
addPagedListListener(Add a |
PagedList<@NonNull T> |
Returns the PagedList currently being displayed by the differ. |
T |
getItem(int index)Get the item from the current PagedList at the specified index. |
int |
Get the number of items currently presented by this Differ. |
void |
Remove a previously registered |
final void |
removePagedListListener(Remove a previously registered callback via |
void |
removePagedListListener(Remove a previously registered |
void |
submitList(PagedList<@NonNull T> pagedList)Pass a new |
void |
submitList(PagedList<@NonNull T> pagedList, Runnable commitCallback)Pass a new PagedList to the differ. |
Public constructors
AsyncPagedListDiffer
public <T extends Object>AsyncPagedListDiffer(
@NonNull RecyclerView.Adapter<@NonNull ?> adapter,
@NonNull DiffUtil.ItemCallback<@NonNull T> diffCallback
)
Convenience for
AsyncPagedListDiffer(
AdapterListUpdateCallback(adapter),
AsyncDifferConfig.Builder<T>(diffCallback).build()
)
| Parameters | |
|---|---|
@NonNull RecyclerView.Adapter<@NonNull ?> adapter |
Adapter that will receive update signals. |
@NonNull DiffUtil.ItemCallback<@NonNull T> diffCallback |
The |
AsyncPagedListDiffer
public <T extends Object>AsyncPagedListDiffer(
@NonNull ListUpdateCallback listUpdateCallback,
@NonNull AsyncDifferConfig<@NonNull T> config
)
Public methods
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 |
|
| See also | |
|---|---|
removeLoadStateListener |
public final void addPagedListListener(
@NonNull Function2<PagedList<@NonNull T>, PagedList<@NonNull T>, Unit> callback
)
Add a callback to receive updates when the current PagedList changes.
| Parameters | |
|---|---|
@NonNull Function2<PagedList<@NonNull T>, PagedList<@NonNull T>, Unit> callback |
to receive updates. |
| See also | |
|---|---|
currentList |
|
removePagedListListener |
public void addPagedListListener(
@NonNull AsyncPagedListDiffer.PagedListListener<@NonNull T> listener
)
Add a PagedListListener to receive updates when the current PagedList changes.
| Parameters | |
|---|---|
@NonNull AsyncPagedListDiffer.PagedListListener<@NonNull T> listener |
Listener to receive updates. |
| See also | |
|---|---|
currentList |
|
removePagedListListener |
public PagedList<@NonNull T> getCurrentList()
Returns the PagedList currently being displayed by the differ.
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.
public T getItem(int index)
Get the item from the current PagedList at the specified index.
Note that this operates on both loaded items and null padding within the PagedList.
| Parameters | |
|---|---|
int index |
Index of item to get, must be >= 0, and < |
| Returns | |
|---|---|
T |
The item, or null, if a null placeholder is at the specified position. |
| Throws | |
|---|---|
kotlin.IndexOutOfBoundsException |
if |
public int getItemCount()
Get the number of items currently presented by this Differ. This value can be directly returned to RecyclerView.Adapter.getItemCount.
| Returns | |
|---|---|
int |
Number of items being presented. |
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 | |
|---|---|
currentList |
|
addPagedListListener |
public final void removePagedListListener(
@NonNull Function2<PagedList<@NonNull T>, PagedList<@NonNull T>, Unit> callback
)
Remove a previously registered callback via addPagedListListener.
| Parameters | |
|---|---|
@NonNull Function2<PagedList<@NonNull T>, PagedList<@NonNull T>, Unit> callback |
Previously registered callback. |
| See also | |
|---|---|
currentList |
|
addPagedListListener |
public void removePagedListListener(
@NonNull AsyncPagedListDiffer.PagedListListener<@NonNull T> listener
)
Remove a previously registered PagedListListener.
| Parameters | |
|---|---|
@NonNull AsyncPagedListDiffer.PagedListListener<@NonNull T> listener |
Previously registered listener. |
| See also | |
|---|---|
currentList |
|
addPagedListListener |
public void submitList(PagedList<@NonNull T> pagedList)
Pass a new PagedList to the differ.
If a PagedList is already present, a diff will be computed asynchronously on a background thread. When the diff is computed, it will be applied (dispatched to the ListUpdateCallback), and the new PagedList will be swapped in as the currentList.
public void submitList(PagedList<@NonNull T> pagedList, Runnable commitCallback)
Pass a new PagedList to the differ.
If a PagedList is already present, a diff will be computed asynchronously on a background thread. When the diff is computed, it will be applied (dispatched to the ListUpdateCallback), and the new PagedList will be swapped in as the current list.
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 |
Runnable commitCallback |
Optional runnable that is executed when the PagedList is committed, if it is committed. |
| Throws | |
|---|---|
kotlin.IllegalStateException |
if previous PagedList wasn't snapshotted correctly. |