Subclasses:

ListItemAdapter, CarDrawerAdapter, PagedListAdapter<T, VH>, ItemBridgeAdapter, GuidedActionAdapter, LeanbackListPreferenceDialogFragment.AdapterSingle, LeanbackListPreferenceDialogFragment.AdapterMulti, SliceAdapter, ConcatAdapter, ListAdapter<T, VH>, FragmentStateAdapter, PreferenceGroupAdapter

Overview

Base class for an Adapter

Adapters provide a binding from an app-specific data set to views that are displayed within a RecyclerView.

Summary

Constructors

Methods

Called when RecyclerView needs a new RecyclerView.ViewHolder of the given type to represent an item.

This new ViewHolder should be constructed with a new View that can represent the items of the given type. You can either create a new View manually or inflate it from an XML layout file.

The new ViewHolder will be used to display items of the adapter using RecyclerView.Adapter. Since it will be re-used to display different items in the data set, it is a good idea to cache references to sub views of the View to avoid unnecessary View calls.

Parameters:

parent: The ViewGroup into which the new View will be added after it is bound to an adapter position.
viewType: The view type of the new View.

Returns:

A new ViewHolder that holds a View of the given view type.

See also: RecyclerView.Adapter.getItemViewType(int), RecyclerView.Adapter

Called by RecyclerView to display the data at the specified position. This method should update the contents of the RecyclerView.ViewHolder.itemView to reflect the item at the given position.

Note that unlike , RecyclerView will not call this method again if the position of the item changes in the data set unless the item itself is invalidated or the new position cannot be determined. For this reason, you should only use the position parameter while acquiring the related data item inside this method and should not keep a copy of it. If you need the position of an item later on (e.g. in a click listener), use RecyclerView.ViewHolder.getBindingAdapterPosition() which will have the updated adapter position. Override RecyclerView.Adapter instead if Adapter can handle efficient partial bind.

Parameters:

holder: The ViewHolder which should be updated to represent the contents of the item at the given position in the data set.
position: The position of the item within the adapter's data set.

Called by RecyclerView to display the data at the specified position. This method should update the contents of the RecyclerView.ViewHolder.itemView to reflect the item at the given position.

Note that unlike , RecyclerView will not call this method again if the position of the item changes in the data set unless the item itself is invalidated or the new position cannot be determined. For this reason, you should only use the position parameter while acquiring the related data item inside this method and should not keep a copy of it. If you need the position of an item later on (e.g. in a click listener), use RecyclerView.ViewHolder.getBindingAdapterPosition() which will have the updated adapter position.

Partial bind vs full bind:

The payloads parameter is a merge list from RecyclerView.Adapter.notifyItemChanged(int, Object) or RecyclerView.Adapter.notifyItemRangeChanged(int, int, Object). If the payloads list is not empty, the ViewHolder is currently bound to old data and Adapter may run an efficient partial update using the payload info. If the payload is empty, Adapter must run a full bind. Adapter should not assume that the payload passed in notify methods will be received by onBindViewHolder(). For example when the view is not attached to the screen, the payload in notifyItemChange() will be simply dropped.

Parameters:

holder: The ViewHolder which should be updated to represent the contents of the item at the given position in the data set.
position: The position of the item within the adapter's data set.
payloads: A non-null list of merged payloads. Can be empty list if requires full update.

Returns the position of the given RecyclerView.ViewHolder in the given RecyclerView.Adapter. If the given RecyclerView.Adapter is not part of this RecyclerView.Adapter, RecyclerView.NO_POSITION is returned.

Parameters:

adapter: The adapter which is a sub adapter of this adapter or itself.
viewHolder: The ViewHolder whose local position in the given adapter will be returned.
localPosition: The position of the given RecyclerView.ViewHolder in this RecyclerView.Adapter.

Returns:

The local position of the given RecyclerView.ViewHolder in this RecyclerView.Adapter or RecyclerView.NO_POSITION if the RecyclerView.ViewHolder is not bound to an item or the given RecyclerView.Adapter is not part of this Adapter (if this Adapter merges other adapters).

This method calls RecyclerView.Adapter.onCreateViewHolder(ViewGroup, int) to create a new RecyclerView.ViewHolder and initializes some private fields to be used by RecyclerView.

See also: RecyclerView.Adapter.onCreateViewHolder(ViewGroup, int)

This method internally calls RecyclerView.Adapter to update the RecyclerView.ViewHolder contents with the item at the given position and also sets up some private fields to be used by RecyclerView. Adapters that merge other adapters should use RecyclerView.Adapter when calling nested adapters so that RecyclerView can track which adapter bound the RecyclerView.ViewHolder to return the correct position from RecyclerView.ViewHolder.getBindingAdapterPosition() method. They should also override the RecyclerView.Adapter method.

Parameters:

holder: The view holder whose contents should be updated
position: The position of the holder with respect to this adapter

See also: RecyclerView.Adapter

Return the view type of the item at position for the purposes of view recycling.

The default implementation of this method returns 0, making the assumption of a single view type for the adapter. Unlike ListView adapters, types need not be contiguous. Consider using id resources to uniquely identify item view types.

Parameters:

position: position to query

Returns:

integer value identifying the type of the view needed to represent the item at position. Type codes need not be contiguous.

Indicates whether each item in the data set can be represented with a unique identifier of type java.lang.Long.

Parameters:

hasStableIds: Whether items in data set have unique identifiers or not.

See also: RecyclerView.Adapter.hasStableIds(), RecyclerView.Adapter.getItemId(int)

Return the stable ID for the item at position. If RecyclerView.Adapter.hasStableIds() would return false this method should return RecyclerView.NO_ID. The default implementation of this method returns RecyclerView.NO_ID.

Parameters:

position: Adapter position to query

Returns:

the stable ID of the item at position

Returns the total number of items in the data set held by the adapter.

Returns:

The total number of items in this adapter.

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. If that item is relocated in the data set, the ID returned for that item should be the same.

Returns:

true if this adapter's items have stable IDs

Called when a view created by this adapter has been recycled.

A view is recycled when a RecyclerView.LayoutManager decides that it no longer needs to be attached to its parent RecyclerView. This can be because it has fallen out of visibility or a set of cached views represented by views still attached to the parent RecyclerView. If an item view has large or expensive data bound to it such as large bitmaps, this may be a good place to release those resources.

RecyclerView calls this method right before clearing ViewHolder's internal data and sending it to RecycledViewPool. This way, if ViewHolder was holding valid information before being recycled, you can call RecyclerView.ViewHolder.getBindingAdapterPosition() to get its adapter position.

Parameters:

holder: The ViewHolder for the view being recycled

Called by the RecyclerView if a ViewHolder created by this Adapter cannot be recycled due to its transient state. Upon receiving this callback, Adapter can clear the animation(s) that effect the View's transient state and return true so that the View can be recycled. Keep in mind that the View in question is already removed from the RecyclerView.

In some cases, it is acceptable to recycle a View although it has transient state. Most of the time, this is a case where the transient state will be cleared in RecyclerView.Adapter call when View is rebound to a new position. For this reason, RecyclerView leaves the decision to the Adapter and uses the return value of this method to decide whether the View should be recycled or not.

Note that when all animations are created by RecyclerView.ItemAnimator, you should never receive this callback because RecyclerView keeps those Views as children until their animations are complete. This callback is useful when children of the item views create animations which may not be easy to implement using an RecyclerView.ItemAnimator.

You should never fix this issue by calling holder.itemView.setHasTransientState(false); unless you've previously called holder.itemView.setHasTransientState(true);. Each View.setHasTransientState(true) call must be matched by a View.setHasTransientState(false) call, otherwise, the state of the View may become inconsistent. You should always prefer to end or cancel animations that are triggering the transient state instead of handling it manually.

Parameters:

holder: The ViewHolder containing the View that could not be recycled due to its transient state.

Returns:

True if the View should be recycled, false otherwise. Note that if this method returns true, RecyclerView will ignore the transient state of the View and recycle it regardless. If this method returns false, RecyclerView will check the View's transient state again before giving a final decision. Default implementation returns false.

Called when a view created by this adapter has been attached to a window.

This can be used as a reasonable signal that the view is about to be seen by the user. If the adapter previously freed any resources in onViewDetachedFromWindow those resources should be restored here.

Parameters:

holder: Holder of the view being attached

Called when a view created by this adapter has been detached from its window.

Becoming detached from the window is not necessarily a permanent condition; the consumer of an Adapter's views may choose to cache views offscreen while they are not visible, attaching and detaching them as appropriate.

Parameters:

holder: Holder of the view being detached

Returns true if one or more observers are attached to this adapter.

Returns:

true if this adapter has observers

Register a new observer to listen for data changes.

The adapter may publish a variety of events describing specific changes. Not all adapters may support all change types and some may fall back to a generic "something changed" event if more specific data is not available.

Components registering observers with an adapter are responsible for unregistering those observers when finished.

Parameters:

observer: Observer to register

See also: RecyclerView.Adapter.unregisterAdapterDataObserver(RecyclerView.AdapterDataObserver)

Unregister an observer currently listening for data changes.

The unregistered observer will no longer receive events about changes to the adapter.

Parameters:

observer: Observer to unregister

See also: RecyclerView.Adapter.registerAdapterDataObserver(RecyclerView.AdapterDataObserver)

Called by RecyclerView when it starts observing this Adapter.

Keep in mind that same adapter may be observed by multiple RecyclerViews.

Parameters:

recyclerView: The RecyclerView instance which started observing this adapter.

See also: RecyclerView.Adapter.onDetachedFromRecyclerView(RecyclerView)

Called by RecyclerView when it stops observing this Adapter.

Parameters:

recyclerView: The RecyclerView instance which stopped observing this adapter.

See also: RecyclerView.Adapter.onAttachedToRecyclerView(RecyclerView)

Notify any registered observers that the data set has changed.

There are two different classes of data change events, item changes and structural changes. Item changes are when a single item has its data updated but no positional changes have occurred. Structural changes are when items are inserted, removed or moved within the data set.

This event does not specify what about the data set has changed, forcing any observers to assume that all existing items and structure may no longer be valid. LayoutManagers will be forced to fully rebind and relayout all visible views.

RecyclerView will attempt to synthesize visible structural change events for adapters that report that they have stable IDs when this method is used. This can help for the purposes of animation and visual object persistence but individual item views will still need to be rebound and relaid out.

If you are writing an adapter it will always be more efficient to use the more specific change events if you can. Rely on notifyDataSetChanged() as a last resort.

See also: RecyclerView.Adapter.notifyItemChanged(int), RecyclerView.Adapter.notifyItemInserted(int), RecyclerView.Adapter.notifyItemRemoved(int), RecyclerView.Adapter.notifyItemRangeChanged(int, int), RecyclerView.Adapter.notifyItemRangeInserted(int, int), RecyclerView.Adapter.notifyItemRangeRemoved(int, int)

Notify any registered observers that the item at position has changed. Equivalent to calling notifyItemChanged(position, null);.

This is an item change event, not a structural change event. It indicates that any reflection of the data at position is out of date and should be updated. The item at position retains the same identity.

Parameters:

position: Position of the item that has changed

See also: RecyclerView.Adapter.notifyItemRangeChanged(int, int)

Notify any registered observers that the item at position has changed with an optional payload object.

This is an item change event, not a structural change event. It indicates that any reflection of the data at position is out of date and should be updated. The item at position retains the same identity.

Client can optionally pass a payload for partial change. These payloads will be merged and may be passed to adapter's RecyclerView.Adapter if the item is already represented by a ViewHolder and it will be rebound to the same ViewHolder. A notifyItemRangeChanged() with null payload will clear all existing payloads on that item and prevent future payload until RecyclerView.Adapter is called. Adapter should not assume that the payload will always be passed to onBindViewHolder(), e.g. when the view is not attached, the payload will be simply dropped.

Parameters:

position: Position of the item that has changed
payload: Optional parameter, use null to identify a "full" update

See also: RecyclerView.Adapter.notifyItemRangeChanged(int, int)

Notify any registered observers that the itemCount items starting at position positionStart have changed. Equivalent to calling notifyItemRangeChanged(position, itemCount, null);.

This is an item change event, not a structural change event. It indicates that any reflection of the data in the given position range is out of date and should be updated. The items in the given range retain the same identity.

Parameters:

positionStart: Position of the first item that has changed
itemCount: Number of items that have changed

See also: RecyclerView.Adapter.notifyItemChanged(int)

Notify any registered observers that the itemCount items starting at position positionStart have changed. An optional payload can be passed to each changed item.

This is an item change event, not a structural change event. It indicates that any reflection of the data in the given position range is out of date and should be updated. The items in the given range retain the same identity.

Client can optionally pass a payload for partial change. These payloads will be merged and may be passed to adapter's RecyclerView.Adapter if the item is already represented by a ViewHolder and it will be rebound to the same ViewHolder. A notifyItemRangeChanged() with null payload will clear all existing payloads on that item and prevent future payload until RecyclerView.Adapter is called. Adapter should not assume that the payload will always be passed to onBindViewHolder(), e.g. when the view is not attached, the payload will be simply dropped.

Parameters:

positionStart: Position of the first item that has changed
itemCount: Number of items that have changed
payload: Optional parameter, use null to identify a "full" update

See also: RecyclerView.Adapter.notifyItemChanged(int)

Notify any registered observers that the item reflected at position has been newly inserted. The item previously at position is now at position position + 1.

This is a structural change event. Representations of other existing items in the data set are still considered up to date and will not be rebound, though their positions may be altered.

Parameters:

position: Position of the newly inserted item in the data set

See also: RecyclerView.Adapter.notifyItemRangeInserted(int, int)

Notify any registered observers that the item reflected at fromPosition has been moved to toPosition.

This is a structural change event. Representations of other existing items in the data set are still considered up to date and will not be rebound, though their positions may be altered.

Parameters:

fromPosition: Previous position of the item.
toPosition: New position of the item.

Notify any registered observers that the currently reflected itemCount items starting at positionStart have been newly inserted. The items previously located at positionStart and beyond can now be found starting at position positionStart + itemCount.

This is a structural change event. Representations of other existing items in the data set are still considered up to date and will not be rebound, though their positions may be altered.

Parameters:

positionStart: Position of the first item that was inserted
itemCount: Number of items inserted

See also: RecyclerView.Adapter.notifyItemInserted(int)

Notify any registered observers that the item previously located at position has been removed from the data set. The items previously located at and after position may now be found at oldPosition - 1.

This is a structural change event. Representations of other existing items in the data set are still considered up to date and will not be rebound, though their positions may be altered.

Parameters:

position: Position of the item that has now been removed

See also: RecyclerView.Adapter.notifyItemRangeRemoved(int, int)

Notify any registered observers that the itemCount items previously located at positionStart have been removed from the data set. The items previously located at and after positionStart + itemCount may now be found at oldPosition - itemCount.

This is a structural change event. Representations of other existing items in the data set are still considered up to date and will not be rebound, though their positions may be altered.

Parameters:

positionStart: Previous position of the first item that was removed
itemCount: Number of items removed from the data set

Sets the state restoration strategy for the Adapter. By default, it is set to RecyclerView.Adapter.StateRestorationPolicy.ALLOW which means RecyclerView expects any set Adapter to be immediately capable of restoring the RecyclerView's saved scroll position.

This behaviour might be undesired if the Adapter's data is loaded asynchronously, and thus unavailable during initial layout (e.g. after Activity rotation). To avoid losing scroll position, you can change this to be either RecyclerView.Adapter.StateRestorationPolicy.PREVENT_WHEN_EMPTY or RecyclerView.Adapter.StateRestorationPolicy.PREVENT. Note that the former means your RecyclerView will restore state as soon as Adapter has 1 or more items while the latter requires you to call RecyclerView.Adapter.setStateRestorationPolicy(RecyclerView.Adapter.StateRestorationPolicy) with either RecyclerView.Adapter.StateRestorationPolicy.ALLOW or RecyclerView.Adapter.StateRestorationPolicy.PREVENT_WHEN_EMPTY again when the Adapter is ready to restore its state.

RecyclerView will still layout even when State restoration is disabled. The behavior of how State is restored is up to the RecyclerView.LayoutManager. All default LayoutManagers will override current state with restored state when state restoration happens (unless an explicit call to RecyclerView.LayoutManager.scrollToPosition(int) is made).

Calling this method after state is restored will not have any effect other than changing the return value of RecyclerView.Adapter.getStateRestorationPolicy().

Parameters:

strategy: The saved state restoration strategy for this Adapter.

See also: RecyclerView.Adapter.getStateRestorationPolicy()

Returns when this Adapter wants to restore the state.

Returns:

The current RecyclerView.Adapter.StateRestorationPolicy for this Adapter. Defaults to RecyclerView.Adapter.StateRestorationPolicy.ALLOW.

See also: RecyclerView.Adapter.setStateRestorationPolicy(RecyclerView.Adapter.StateRestorationPolicy)