Cocoa Programming for OS X: The Big Nerd Ranch Guide

22 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.

The user can perform several different operations by dragging from one application to another, or even between views in the same application. These operations are represented by the NSDragOperation type:

s​t​r​u​c​t​ ​N​S​D​r​a​g​O​p​e​r​a​t​i​o​n​ ​:​ ​R​a​w​O​p​t​i​o​n​S​e​t​T​y​p​e​ ...