C H A P T E R 1 2

Drag and Drop

When content is dropped into a window in which something is selected, your application should deselect everything in the destination before the drop, rather than replacing the selection with the dragged item.

Feedback for an Invalid Drop

If a user attempts to drop an item on a destination that does not accept it, the item zooms from its mouse-up location back to its source location (a “zoomback”). The zoomback behavior should also occur when a drop inside a valid destination does not result in a successful operation. The Drag Manager provides this feedback when it determines that no receiver requested the sender’s information.

If the user attempts to drag multiple items to a destination that does not accept all of the items, none of the items should be accepted. In such cases you could display a dialog informing the user of the type of data the destination accepts and which items in the dragged set cannot be accepted.

Clippings

When an item is dragged from an application or a Finder window to the desktop, the Finder creates a clipping that contains the data in the dragged item. If discontinuous selections are dragged from a source to the Finder, a separate clipping is created for each selected item.

Your application should provide a number of representations (such as TEXT, PICT, and native formats) to ensure flexibility with different subsequent destinations. Regardless of which representations are stored, round-trip data integrity should be preserved; a clipping dragged back into its source should be identical to the original item.

Apple Computer, Inc. June 2002