When your app inserts new items into the collection view, the collection view calls this method for each item you insert. Because new items are not yet visible in the collection view, the attributes you return represent the item’s starting state. For example, you might return attributes that position the item offscreen or set its initial alpha to 0. The collection view uses the attributes you return as the starting point for any animations. (The end point of the animation is the item’s new location and attributes.) If you return nil, the layout uses the item’s final attributes for both the start point and end point of the animation.
The default implementation of this method returns nil. Subclasses are expected to override this method, as needed, and provide any initial attributes.

If you return nil, the layout uses the item’s final attributes for both the start point and end point of the animation.