SimpleItemAnimator

abstract fun animateAdd(holder: RecyclerView.ViewHolder!): Boolean

Called when an item is added to the RecyclerView. Implementors can choose whether and how to animate that change, but must always call dispatchAddFinished when done, either immediately (if no animation will occur) or after the animation actually finishes. The return value indicates whether an animation has been set up and whether the ItemAnimator's runPendingAnimations method should be called at the next opportunity. This mechanism allows ItemAnimator to set up individual animations as separate calls to animateAdd(), animateMove(), animateRemove(), and animateChange come in one by one, then start the animations together in the later call to runPendingAnimations.

This method may also be called for appearing items which were already in the RecyclerView, but for which the system does not have enough information to animate them into view. In that case, the default animation for adding items is run on those items as well.

fun animateAppearance(
    viewHolder: RecyclerView.ViewHolder,
    preLayoutInfo: RecyclerView.ItemAnimator.ItemHolderInfo?,
    postLayoutInfo: RecyclerView.ItemAnimator.ItemHolderInfo
): Boolean

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

fun animateChange(
    oldHolder: RecyclerView.ViewHolder,
    newHolder: RecyclerView.ViewHolder,
    preLayoutInfo: RecyclerView.ItemAnimator.ItemHolderInfo,
    postLayoutInfo: RecyclerView.ItemAnimator.ItemHolderInfo
): Boolean

Called by the RecyclerView when an adapter item is present both before and after the layout and RecyclerView has received a notifyItemChanged 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 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. 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 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 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 for each distinct ViewHolder when their animation is complete (or instantly call dispatchAnimationFinished if it decides not to animate the view).

If oldHolder and newHolder are the same instance, you should call dispatchAnimationFinishedonly 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.

abstract fun animateChange(
    oldHolder: RecyclerView.ViewHolder!,
    newHolder: RecyclerView.ViewHolder!,
    fromLeft: Int,
    fromTop: Int,
    toLeft: Int,
    toTop: Int
): Boolean

Called when an item is changed in the RecyclerView, as indicated by a call to notifyItemChanged or notifyItemRangeChanged.

Implementers can choose whether and how to animate changes, but must always call dispatchChangeFinished for each non-null distinct ViewHolder, either immediately (if no animation will occur) or after the animation actually finishes. If the oldHolder is the same ViewHolder as the newHolder, you must call dispatchChangeFinished once and only once. In that case, the second parameter of dispatchChangeFinished is ignored.

The return value indicates whether an animation has been set up and whether the ItemAnimator's runPendingAnimations method should be called at the next opportunity. This mechanism allows ItemAnimator to set up individual animations as separate calls to animateAdd(), animateMove(), animateRemove(), and animateChange come in one by one, then start the animations together in the later call to runPendingAnimations.

fun animateDisappearance(
    viewHolder: RecyclerView.ViewHolder,
    preLayoutInfo: RecyclerView.ItemAnimator.ItemHolderInfo,
    postLayoutInfo: RecyclerView.ItemAnimator.ItemHolderInfo?
): Boolean

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.

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 and the response of that call will be passed to this method as the postLayoutInfo.

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

abstract fun animateMove(
    holder: RecyclerView.ViewHolder!,
    fromX: Int,
    fromY: Int,
    toX: Int,
    toY: Int
): Boolean

Called when an item is moved in the RecyclerView. Implementors can choose whether and how to animate that change, but must always call dispatchMoveFinished when done, either immediately (if no animation will occur) or after the animation actually finishes. The return value indicates whether an animation has been set up and whether the ItemAnimator's runPendingAnimations method should be called at the next opportunity. This mechanism allows ItemAnimator to set up individual animations as separate calls to animateAdd(), animateMove(), animateRemove(), and animateChange come in one by one, then start the animations together in the later call to runPendingAnimations.

fun animatePersistence(
    viewHolder: RecyclerView.ViewHolder,
    preLayoutInfo: RecyclerView.ItemAnimator.ItemHolderInfo,
    postLayoutInfo: RecyclerView.ItemAnimator.ItemHolderInfo
): Boolean

Called by the RecyclerView when a ViewHolder is present in both before and after the layout and RecyclerView has not received a notifyItemChanged 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 and return false.

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

abstract fun animateRemove(holder: RecyclerView.ViewHolder!): Boolean

Called when an item is removed from the RecyclerView. Implementors can choose whether and how to animate that change, but must always call dispatchRemoveFinished when done, either immediately (if no animation will occur) or after the animation actually finishes. The return value indicates whether an animation has been set up and whether the ItemAnimator's runPendingAnimations method should be called at the next opportunity. This mechanism allows ItemAnimator to set up individual animations as separate calls to animateAdd(), animateMove(), animateRemove(), and animateChange come in one by one, then start the animations together in the later call to runPendingAnimations.

This method may also be called for disappearing items which continue to exist in the RecyclerView, but for which the system does not have enough information to animate them out of view. In that case, the default animation for removing items is run on those items as well.

fun canReuseUpdatedViewHolder(viewHolder: RecyclerView.ViewHolder): Boolean

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 still has the same type ( Adapter#getItemViewType(int)). Otherwise, ItemAnimator will always receive both s 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.

fun dispatchAddFinished(item: RecyclerView.ViewHolder!): Unit

Method to be called by subclasses when an add animation is done.

fun dispatchAddStarting(item: RecyclerView.ViewHolder!): Unit

Method to be called by subclasses when an add animation is being started.

fun dispatchChangeFinished(item: RecyclerView.ViewHolder!, oldItem: Boolean): Unit

Method to be called by subclasses when a change animation is done.

fun dispatchChangeStarting(item: RecyclerView.ViewHolder!, oldItem: Boolean): Unit

Method to be called by subclasses when a change animation is being started.

fun dispatchMoveFinished(item: RecyclerView.ViewHolder!): Unit

Method to be called by subclasses when a move animation is done.

fun dispatchMoveStarting(item: RecyclerView.ViewHolder!): Unit

Method to be called by subclasses when a move animation is being started.

fun dispatchRemoveFinished(item: RecyclerView.ViewHolder!): Unit

Method to be called by subclasses when a remove animation is done.

fun dispatchRemoveStarting(item: RecyclerView.ViewHolder!): Unit

Method to be called by subclasses when a remove animation is being started.

fun getSupportsChangeAnimations(): Boolean

Returns whether this ItemAnimator supports animations of change events.

fun onAddFinished(item: RecyclerView.ViewHolder!): Unit

Called when an add animation has ended on the given ViewHolder. The default implementation does nothing. Subclasses may wish to override this method to handle any ViewHolder-specific operations linked to animation lifecycles.

fun onAddStarting(item: RecyclerView.ViewHolder!): Unit

Called when an add animation is being started on the given ViewHolder. The default implementation does nothing. Subclasses may wish to override this method to handle any ViewHolder-specific operations linked to animation lifecycles.

fun onChangeFinished(item: RecyclerView.ViewHolder!, oldItem: Boolean): Unit

Called when a change animation has ended on the given ViewHolder. The default implementation does nothing. Subclasses may wish to override this method to handle any ViewHolder-specific operations linked to animation lifecycles.

fun onChangeStarting(item: RecyclerView.ViewHolder!, oldItem: Boolean): Unit

Called when a change animation is being started on the given ViewHolder. The default implementation does nothing. Subclasses may wish to override this method to handle any ViewHolder-specific operations linked to animation lifecycles.

fun onMoveFinished(item: RecyclerView.ViewHolder!): Unit

Called when a move animation has ended on the given ViewHolder. The default implementation does nothing. Subclasses may wish to override this method to handle any ViewHolder-specific operations linked to animation lifecycles.

fun onMoveStarting(item: RecyclerView.ViewHolder!): Unit

Called when a move animation is being started on the given ViewHolder. The default implementation does nothing. Subclasses may wish to override this method to handle any ViewHolder-specific operations linked to animation lifecycles.

fun onRemoveFinished(item: RecyclerView.ViewHolder!): Unit

Called when a remove animation has ended on the given ViewHolder. The default implementation does nothing. Subclasses may wish to override this method to handle any ViewHolder-specific operations linked to animation lifecycles.

fun onRemoveStarting(item: RecyclerView.ViewHolder!): Unit

Called when a remove animation is being started on the given ViewHolder. The default implementation does nothing. Subclasses may wish to override this method to handle any ViewHolder-specific operations linked to animation lifecycles.

fun setSupportsChangeAnimations(supportsChangeAnimations: Boolean): Unit

Sets whether this ItemAnimator supports animations of item change events. If you set this property to false, actions on the data set which change the contents of items will not be animated. What those animations do is left up to the discretion of the ItemAnimator subclass, in its animateChange implementation. The value of this property is true by default.