Tells the delegate that the specified supplementary view is about to be displayed in the collection view.
- iOS 8.0+
- tvOS 9.0+
The collection view object that is adding the supplementary view.
The view being added.
The type of the supplementary view. This string is defined by the layout that presents the view.
The index path of the data item that the supplementary view represents.
The collection view calls this method before adding a supplementary view to its content. Use this method to detect view additions, as opposed to monitoring the view itself to see when it appears.