ListAdapter
public
abstract
class
ListAdapter
extends Adapter<VH extends RecyclerView.ViewHolder>
java.lang.Object | ||
↳ | androidx.recyclerview.widget.RecyclerView.Adapter<VH extends androidx.recyclerview.widget.RecyclerView.ViewHolder> | |
↳ | androidx.recyclerview.widget.ListAdapter<T, VH extends androidx.recyclerview.widget.RecyclerView.ViewHolder> |
RecyclerView.Adapter
base class for presenting List data in a
RecyclerView
, including computing diffs between Lists on a background thread.
This class is a convenience wrapper around AsyncListDiffer
that implements Adapter common
default behavior for item access and counting.
While using a LiveData<List> is an easy way to provide data to the adapter, it isn't required
- you can use submitList(List)
when new lists are available.
A complete usage pattern with Room would look like this:
@Dao interface UserDao { @Query("SELECT * FROM user ORDER BY lastName ASC") public abstract LiveData<List<User>> usersByLastName(); } class MyViewModel extends ViewModel { public final LiveData<List<User>> usersList; public MyViewModel(UserDao userDao) { usersList = userDao.usersByLastName(); } } 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, list -> adapter.submitList(list)); recyclerView.setAdapter(adapter); } } class UserAdapter extends ListAdapter<User, UserViewHolder> { public UserAdapter() { super(User.DIFF_CALLBACK); } @Override public void onBindViewHolder(UserViewHolder holder, int position) { holder.bindTo(getItem(position)); } 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
AsyncListDiffer
, which provides custom mapping from diff events
to adapter positions.
Summary
Protected constructors | |
---|---|
ListAdapter(ItemCallback<T> diffCallback)
|
|
ListAdapter(AsyncDifferConfig<T> config)
|
Public methods | |
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List<T>
|
getCurrentList()
Get the current List - any diffing to present this list has already been computed and dispatched via the ListUpdateCallback. |
int
|
getItemCount()
Returns the total number of items in the data set held by the adapter. |
void
|
onCurrentListChanged(List<T> previousList, List<T> currentList)
Called when the current List is updated. |
void
|
submitList(List<T> list)
Submits a new list to be diffed, and displayed. |
void
|
submitList(List<T> list, Runnable commitCallback)
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
ListAdapter
protected ListAdapter (ItemCallback<T> diffCallback)
Parameters | |
---|---|
diffCallback |
ItemCallback |
Public methods
getCurrentList
public List<T> getCurrentList ()
Get the current List - any diffing to present this list has already been computed and dispatched via the ListUpdateCallback.
If a null
List, or no List has been submitted, an empty list will be returned.
The returned list may not be mutated - mutations to content must be done through
submitList(List)
.
Returns | |
---|---|
List<T> |
The list currently being displayed. |
See also:
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 (List<T> previousList, List<T> currentList)
Called when the current List is updated.
If a null
List is passed to submitList(List)
, or no List has been
submitted, the current List is represented as an empty List.
Parameters | |
---|---|
previousList |
List : List that was displayed previously. |
currentList |
List : new List being displayed, will be empty if null was passed to
submitList(List) . |
See also:
submitList
public void submitList (List<T> list)
Submits a new list to be diffed, and 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 | |
---|---|
list |
List : The new list to be displayed.
|
submitList
public void submitList (List<T> list, 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 List is committed, but note that it may not be executed. If List B is submitted immediately after List A, and is committed directly, the callback associated with List A will not be run.
Parameters | |
---|---|
list |
List : The new list to be displayed. |
commitCallback |
Runnable : Optional runnable that is executed when the List is committed, if
it is committed.
|
Protected methods
getItem
protected T getItem (int position)
Parameters | |
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position |
int |
Returns | |
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T |