PagedListAdapter
public
abstract
class
PagedListAdapter
extends Adapter<VH extends RecyclerView.ViewHolder>
java.lang.Object | ||
↳ | androidx.recyclerview.widget.RecyclerView.Adapter<VH extends androidx.recyclerview.widget.RecyclerView.ViewHolder> | |
↳ | androidx.paging.PagedListAdapter<T, VH extends androidx.recyclerview.widget.RecyclerView.ViewHolder> |
RecyclerView.Adapter
base class for presenting paged data from
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 LiveData<PagedList> is an easy way to provide data to the adapter, it isn't
required - you can use submitList(PagedList)
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 = ViewModelProviders.of(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.
Summary
Protected constructors | |
---|---|
PagedListAdapter(ItemCallback<T> diffCallback)
Creates a PagedListAdapter with default threading and
|
|
PagedListAdapter(AsyncDifferConfig<T> config)
|
Public methods | |
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PagedList<T>
|
getCurrentList()
Returns the PagedList currently being displayed by the Adapter. |
int
|
getItemCount()
Returns the total number of items in the data set held by the adapter. |
void
|
onCurrentListChanged(PagedList<T> currentList)
This method is deprecated.
Use the two argument variant instead:
|
void
|
onCurrentListChanged(PagedList<T> previousList, PagedList<T> currentList)
Called when the current PagedList is updated. |
void
|
submitList(PagedList<T> pagedList, Runnable commitCallback)
Set the new list to be displayed. |
void
|
submitList(PagedList<T> pagedList)
Set the new list to be displayed. |
Protected methods | |
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T
|
getItem(int position)
|
Inherited methods | |
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Protected constructors
PagedListAdapter
protected PagedListAdapter (ItemCallback<T> diffCallback)
Creates a PagedListAdapter with default threading and
ListUpdateCallback
.
Convenience for PagedListAdapter(AsyncDifferConfig)
, which uses default threading
behavior.
Parameters | |
---|---|
diffCallback |
ItemCallback : The DiffUtil.ItemCallback instance to
compare items in the list.
|
PagedListAdapter
protected PagedListAdapter (AsyncDifferConfig<T> config)
Parameters | |
---|---|
config |
AsyncDifferConfig |
Public methods
getCurrentList
public PagedList<T> getCurrentList ()
Returns the PagedList currently being displayed by the Adapter.
This is not necessarily the most recent list passed to submitList(PagedList)
,
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<T> |
The list currently being displayed. |
getItemCount
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
public void onCurrentListChanged (PagedList<T> currentList)
This method is deprecated.
Use the two argument variant instead:
onCurrentListChanged(PagedList, PagedList)
Called when the current PagedList is updated.
This may be dispatched as part of submitList(PagedList)
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 | |
---|---|
currentList |
PagedList : new PagedList being displayed, may be null. |
See also:
onCurrentListChanged
public void onCurrentListChanged (PagedList<T> previousList, PagedList<T> currentList)
Called when the current PagedList is updated.
This may be dispatched as part of submitList(PagedList)
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 | |
---|---|
previousList |
PagedList : PagedList that was previously displayed, may be null. |
currentList |
PagedList : new PagedList being displayed, may be null. |
See also:
submitList
public void submitList (PagedList<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 |
PagedList : The new list to be displayed. |
commitCallback |
Runnable : Optional runnable that is executed when the PagedList is committed, if
it is committed.
|
submitList
public void submitList (PagedList<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 |
PagedList : The new list to be displayed.
|
Protected methods
getItem
protected T getItem (int position)
Parameters | |
---|---|
position |
int |
Returns | |
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T |