Returns the starting layout information for a supplementary view being added to the collection view.
- macOS 10.11+
The type of the supplementary view being added.
The index path of the supplementary view. You can use this path to retrieve any relevant information from the collection view’s data source.
The layout attributes object that describes the supplementary view’s position and properties at the start of animations.
When your layout object adds supplementary views in response to other changes in the collection view, the collection view calls this method for each supplementary view before animating it onscreen. Because new supplementary views are not yet visible in the collection view, the attributes you return represent the view’s starting state. For example, you might return attributes that position the supplementary view 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 view’s new location and attributes.) If you return
nil, the layout uses the supplementary view’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.