Chapter 23. Drag-and-Drop
Drag-and-drop is little more than a flashy copy-and-paste operation. When the drag starts, some data is copied onto the dragging pasteboard. When the drop occurs, the data is 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 things can happen when data is 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 ...
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