Chapter 20. Drag-and-Drop
Drag-and-drop is little more than a flashy copy-and-paste. When the drag starts, some data are copied onto the dragging pasteboard. When the drop occurs, the data are read off the dragging pasteboard. The only thing that makes this technique trickier than copy-and-paste is that users need feedback: an image that appears as they drag, a view that becomes highlighted when they drag into it, and maybe a big gulping sound when they drop the image.
Several different things can happen when data are dragged from one application to another: Nothing may happen, a copy of the data may be created, or a link to the existing data may be created. Constants represent these operations:
NSDragOperationNone NSDragOperationCopy NSDragOperationLink ...