RecyclerView.Adapter

RecyclerView.Adapter

RecyclerView.Adapter ()

bindViewHolder

void bindViewHolder (VH holder, 
                int position)

This method internally calls onBindViewHolder(ViewHolder, int) 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.

createViewHolder

VH createViewHolder (ViewGroup parent, 
                int viewType)

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

getItemCount

int getItemCount ()

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

getItemId

long getItemId (int position)

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

getItemViewType

int getItemViewType (int position)

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.

hasObservers

boolean hasObservers ()

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

hasStableIds

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

notifyDataSetChanged

void notifyDataSetChanged ()

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.

notifyItemChanged

void notifyItemChanged (int position, 
                Object payload)

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 onBindViewHolder(ViewHolder, int, List) 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 onBindViewHolder(ViewHolder, int, List) 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.

notifyItemChanged

void notifyItemChanged (int position)

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.

notifyItemInserted

void notifyItemInserted (int position)

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.

notifyItemMoved

void notifyItemMoved (int fromPosition, 
                int toPosition)

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.

notifyItemRangeChanged

void notifyItemRangeChanged (int positionStart, 
                int itemCount, 
                Object payload)

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 onBindViewHolder(ViewHolder, int, List) 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 onBindViewHolder(ViewHolder, int, List) 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.

notifyItemRangeChanged

void notifyItemRangeChanged (int positionStart, 
                int itemCount)

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.

notifyItemRangeInserted

void notifyItemRangeInserted (int positionStart, 
                int itemCount)

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.

notifyItemRangeRemoved

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. 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.

notifyItemRemoved

void notifyItemRemoved (int position)

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.

onAttachedToRecyclerView

void onAttachedToRecyclerView (RecyclerView recyclerView)

Called by RecyclerView when it starts observing this Adapter.

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

onBindViewHolder

void onBindViewHolder (VH holder, 
                int position)

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

Note that unlike ListView, 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 getAdapterPosition() which will have the updated adapter position. Override onBindViewHolder(ViewHolder, int, List) instead if Adapter can handle efficient partial bind.

onBindViewHolder

void onBindViewHolder (VH holder, 
                int position, 
                List<Object> payloads)

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

Note that unlike ListView, 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 getAdapterPosition() which will have the updated adapter position.

Partial bind vs full bind:

The payloads parameter is a merge list from notifyItemChanged(int, Object) or 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.

onCreateViewHolder

VH onCreateViewHolder (ViewGroup parent, 
                int viewType)

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 onBindViewHolder(ViewHolder, int, List). 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 findViewById(int) calls.

onDetachedFromRecyclerView

void onDetachedFromRecyclerView (RecyclerView recyclerView)

Called by RecyclerView when it stops observing this Adapter.

onFailedToRecycleView

boolean onFailedToRecycleView (VH holder)

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 onBindViewHolder(ViewHolder, int) 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.

onViewAttachedToWindow

void onViewAttachedToWindow (VH holder)

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.

onViewDetachedFromWindow

void onViewDetachedFromWindow (VH holder)

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.

onViewRecycled

void onViewRecycled (VH holder)

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 getAdapterPosition() to get its adapter position.

registerAdapterDataObserver

void registerAdapterDataObserver (RecyclerView.AdapterDataObserver observer)

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.

setHasStableIds

void setHasStableIds (boolean hasStableIds)

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

unregisterAdapterDataObserver

void unregisterAdapterDataObserver (RecyclerView.AdapterDataObserver observer)

Unregister an observer currently listening for data changes.

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