RecyclerView.ItemAnimator

FLAG_APPEARED_IN_PRE_LAYOUT

int FLAG_APPEARED_IN_PRE_LAYOUT

This ViewHolder was not laid out but has been added to the layout in pre-layout state by the RecyclerView.LayoutManager. This means that the item was already in the Adapter but invisible and it may become visible in the post layout phase. LayoutManagers may prefer to add new items in pre-layout to specify their virtual location when they are invisible (e.g. to specify the item should animate in from below the visible area).

Constant Value: 4096 (0x00001000)

FLAG_CHANGED

int FLAG_CHANGED

The Item represented by this ViewHolder is updated.

Constant Value: 2 (0x00000002)

FLAG_INVALIDATED

int FLAG_INVALIDATED

Adapter notifyDataSetChanged() has been called and the content represented by this ViewHolder is invalid.

Constant Value: 4 (0x00000004)

FLAG_MOVED

int FLAG_MOVED

The position of the Item represented by this ViewHolder has been changed. This flag is not bound to notifyItemMoved(int, int). It might be set in response to any adapter change that may have a side effect on this item. (e.g. The item before this one has been removed from the Adapter).

Constant Value: 2048 (0x00000800)

FLAG_REMOVED

int FLAG_REMOVED

The Item represented by this ViewHolder is removed from the adapter.

Constant Value: 8 (0x00000008)

RecyclerView.ItemAnimator

RecyclerView.ItemAnimator ()

animateAppearance

boolean animateAppearance (RecyclerView.ViewHolder viewHolder, 
                RecyclerView.ItemAnimator.ItemHolderInfo preLayoutInfo, 
                RecyclerView.ItemAnimator.ItemHolderInfo postLayoutInfo)

Called by the RecyclerView when a ViewHolder is added to the layout.

In detail, this means that the ViewHolder was not a child when the layout started but has been added by the LayoutManager. It might be newly added to the adapter or simply become visible due to other factors.

ItemAnimator must call dispatchAnimationFinished(ViewHolder) when the animation is complete (or instantly call dispatchAnimationFinished(ViewHolder) if it decides not to animate the view).

animateChange

boolean animateChange (RecyclerView.ViewHolder oldHolder, 
                RecyclerView.ViewHolder newHolder, 
                RecyclerView.ItemAnimator.ItemHolderInfo preLayoutInfo, 
                RecyclerView.ItemAnimator.ItemHolderInfo postLayoutInfo)

Called by the RecyclerView when an adapter item is present both before and after the layout and RecyclerView has received a notifyItemChanged(int) call for it. This method may also be called when notifyDataSetChanged() is called and adapter has stable ids so that RecyclerView could still rebind views to the same ViewHolders. If viewType changes when notifyDataSetChanged() is called, this method will not be called, instead, animateAppearance(ViewHolder, ItemHolderInfo, ItemHolderInfo) will be called for the new ViewHolder and the old one will be recycled.

If this method is called due to a notifyDataSetChanged() call, there is a good possibility that item contents didn't really change but it is rebound from the adapter. DefaultItemAnimator will skip animating the View if its location on the screen didn't change and your animator should handle this case as well and avoid creating unnecessary animations.

When an item is updated, ItemAnimator has a chance to ask RecyclerView to keep the previous presentation of the item as-is and supply a new ViewHolder for the updated presentation (see: canReuseUpdatedViewHolder(ViewHolder, List). This is useful if you don't know the contents of the Item and would like to cross-fade the old and the new one (DefaultItemAnimator uses this technique).

When you are writing a custom item animator for your layout, it might be more performant and elegant to re-use the same ViewHolder and animate the content changes manually.

When notifyItemChanged(int) is called, the Item's view type may change. If the Item's view type has changed or ItemAnimator returned false for this ViewHolder when canReuseUpdatedViewHolder(ViewHolder, List) was called, the oldHolder and newHolder will be different ViewHolder instances which represent the same Item. In that case, only the new ViewHolder is visible to the LayoutManager but RecyclerView keeps old ViewHolder attached for animations.

ItemAnimator must call dispatchAnimationFinished(ViewHolder) for each distinct ViewHolder when their animation is complete (or instantly call dispatchAnimationFinished(ViewHolder) if it decides not to animate the view).

If oldHolder and newHolder are the same instance, you should call dispatchAnimationFinished(ViewHolder) only once.

Note that when a ViewHolder both changes and disappears in the same layout pass, the animation callback method which will be called by the RecyclerView depends on the ItemAnimator's decision whether to re-use the same ViewHolder or not, and also the LayoutManager's decision whether to layout the changed version of a disappearing ViewHolder or not. RecyclerView will call animateChange instead of animateDisappearance if and only if the ItemAnimator returns false from canReuseUpdatedViewHolder and the LayoutManager lays out a new disappearing view that holds the updated information. Built-in LayoutManagers try to avoid laying out updated versions of disappearing views.

animateDisappearance

boolean animateDisappearance (RecyclerView.ViewHolder viewHolder, 
                RecyclerView.ItemAnimator.ItemHolderInfo preLayoutInfo, 
                RecyclerView.ItemAnimator.ItemHolderInfo postLayoutInfo)

Called by the RecyclerView when a ViewHolder has disappeared from the layout.

This means that the View was a child of the LayoutManager when layout started but has been removed by the LayoutManager. It might have been removed from the adapter or simply become invisible due to other factors. You can distinguish these two cases by checking the change flags that were passed to recordPreLayoutInformation(State, ViewHolder, int, List).

Note that when a ViewHolder both changes and disappears in the same layout pass, the animation callback method which will be called by the RecyclerView depends on the ItemAnimator's decision whether to re-use the same ViewHolder or not, and also the LayoutManager's decision whether to layout the changed version of a disappearing ViewHolder or not. RecyclerView will call animateChange instead of animateDisappearance if and only if the ItemAnimator returns false from canReuseUpdatedViewHolder and the LayoutManager lays out a new disappearing view that holds the updated information. Built-in LayoutManagers try to avoid laying out updated versions of disappearing views.

If LayoutManager supports predictive animations, it might provide a target disappear location for the View by laying it out in that location. When that happens, RecyclerView will call recordPostLayoutInformation(State, ViewHolder) and the response of that call will be passed to this method as the postLayoutInfo.

ItemAnimator must call dispatchAnimationFinished(ViewHolder) when the animation is complete (or instantly call dispatchAnimationFinished(ViewHolder) if it decides not to animate the view).

animatePersistence

boolean animatePersistence (RecyclerView.ViewHolder viewHolder, 
                RecyclerView.ItemAnimator.ItemHolderInfo preLayoutInfo, 
                RecyclerView.ItemAnimator.ItemHolderInfo postLayoutInfo)

Called by the RecyclerView when a ViewHolder is present in both before and after the layout and RecyclerView has not received a notifyItemChanged(int) call for it or a notifyDataSetChanged() call.

This ViewHolder still represents the same data that it was representing when the layout started but its position / size may be changed by the LayoutManager.

If the Item's layout position didn't change, RecyclerView still calls this method because it does not track this information (or does not necessarily know that an animation is not required). Your ItemAnimator should handle this case and if there is nothing to animate, it should call dispatchAnimationFinished(ViewHolder) and return false.

ItemAnimator must call dispatchAnimationFinished(ViewHolder) when the animation is complete (or instantly call dispatchAnimationFinished(ViewHolder) if it decides not to animate the view).

canReuseUpdatedViewHolder

boolean canReuseUpdatedViewHolder (RecyclerView.ViewHolder viewHolder, 
                List<Object> payloads)

When an item is changed, ItemAnimator can decide whether it wants to re-use the same ViewHolder for animations or RecyclerView should create a copy of the item and ItemAnimator will use both to run the animation (e.g. cross-fade).

Note that this method will only be called if the RecyclerView.ViewHolder still has the same type (getItemViewType(int)). Otherwise, ItemAnimator will always receive both RecyclerView.ViewHolders in the animateChange(ViewHolder, ViewHolder, ItemHolderInfo, ItemHolderInfo) method.

canReuseUpdatedViewHolder

boolean canReuseUpdatedViewHolder (RecyclerView.ViewHolder viewHolder)

When an item is changed, ItemAnimator can decide whether it wants to re-use the same ViewHolder for animations or RecyclerView should create a copy of the item and ItemAnimator will use both to run the animation (e.g. cross-fade).

Note that this method will only be called if the RecyclerView.ViewHolder still has the same type (getItemViewType(int)). Otherwise, ItemAnimator will always receive both RecyclerView.ViewHolders in the animateChange(ViewHolder, ViewHolder, ItemHolderInfo, ItemHolderInfo) method.

If your application is using change payloads, you can override canReuseUpdatedViewHolder(ViewHolder, List) to decide based on payloads.

dispatchAnimationFinished

void dispatchAnimationFinished (RecyclerView.ViewHolder viewHolder)

Method to be called by subclasses when an animation is finished.

For each call RecyclerView makes to animateAppearance(),