ListAdapter

Artifact: androidx.recyclerview:recyclerview

Added in 1.0.0

Kotlin |Java

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

java.lang.Object
↳	androidx.recyclerview.widget.RecyclerView.Adapter
	↳	androidx.recyclerview.widget.ListAdapter

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 is an easy way to provide data to the adapter, it isn't required - you can use submitList 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.

Parameters
`<T>`	Type of the Lists this Adapter will receive.
`<VH extends RecyclerView.ViewHolder>`	A class that extends ViewHolder that will be used by the adapter.

Summary

Protected constructors
`ListAdapter(@NonNull AsyncDifferConfig<T> config)`
`ListAdapter(@NonNull DiffUtil.ItemCallback<T> diffCallback)`

Public methods
`@NonNull 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( @NonNull List<T> previousList, @NonNull List<T> currentList )` Called when the current List is updated.
`void`	`submitList(@Nullable List<T> list)` Submits a new list to be diffed, and displayed.
`void`	`submitList(@Nullable List<T> list, @Nullable Runnable commitCallback)` Set the new list to be displayed.

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`	`findRelativeAdapterPositionIn( @NonNull RecyclerView.Adapter<RecyclerView.ViewHolder> adapter, @NonNull RecyclerView.ViewHolder viewHolder, int localPosition )` 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`	`getStateRestorationPolicy()` Returns when this Adapter wants to restore the state.
`final boolean`	`hasObservers()` Returns true if one or more observers are attached to this adapter.
`final boolean`	`hasStableIds()` 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`	`notifyDataSetChanged()` 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`	`onAttachedToRecyclerView(@NonNull RecyclerView recyclerView)` 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<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`	`onDetachedFromRecyclerView(@NonNull RecyclerView recyclerView)` Called by RecyclerView when it stops observing this Adapter.
`boolean`	`onFailedToRecycleView(@NonNull VH holder)` Called by the RecyclerView if a ViewHolder created by this Adapter cannot be recycled due to its transient state.
`void`	`onViewAttachedToWindow(@NonNull VH holder)` Called when a view created by this adapter has been attached to a window.
`void`	`onViewDetachedFromWindow(@NonNull VH holder)` 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`	`registerAdapterDataObserver( @NonNull RecyclerView.AdapterDataObserver observer )` 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`	`setStateRestorationPolicy( @NonNull RecyclerView.Adapter.StateRestorationPolicy strategy )` Sets the state restoration strategy for the Adapter.
`void`	`unregisterAdapterDataObserver( @NonNull RecyclerView.AdapterDataObserver observer )` Unregister an observer currently listening for data changes.

Protected constructors

Added in 1.0.0

protected ListAdapter(@NonNull AsyncDifferConfig<T> config)

Added in 1.0.0

protected ListAdapter(@NonNull DiffUtil.ItemCallback<T> diffCallback)

Public methods

getCurrentList

Added in 1.1.0

public @NonNull 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.

Returns
`@NonNull List<T>`	The list currently being displayed.

See also
`onCurrentListChanged`

getItemCount

Added in 1.4.0

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 1.1.0

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

Called when the current List is updated.

If a null List is passed to submitList, or no List has been submitted, the current List is represented as an empty List.

Parameters
`@NonNull List<T> previousList`	List that was displayed previously.
`@NonNull List<T> currentList`	new List being displayed, will be empty if `null` was passed to `submitList`.

See also
`getCurrentList`

submitList

Added in 1.0.0

public void submitList(@Nullable 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
`@Nullable List<T> list`	The new list to be displayed.

submitList

Added in 1.1.0

public void submitList(@Nullable List<T> list, @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 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
`@Nullable List<T> list`	The new list to be displayed.
`@Nullable Runnable commitCallback`	Optional runnable that is executed when the List is committed, if it is committed.

Protected methods

getItem

Added in 1.0.0

protected T getItem(int position)