Returns an appropriate drag image for the drag initiated by the specified event.
- macOS 10.0+
The event that initiated the drag session.
On return, the lower-left point of the image in view coordinates.
An appropriate drag image for the drag initiated by
event. May be
nil, in which case a default icon will be used.
This method is used by
drag. It can be called by others who need such an image, or can be overridden by subclasses to return a different image.