C H A P T E R 9

Drag and Drop

Move Versus Copy

If the source and destination are in the same container (for example, a window or a volume), a drag-and-drop operation is interpreted as a move (that is, cut and paste). Dragging an item from one container to another initiates a copy (copy and paste). The user can perform a copy operation within the same container by pressing the Option key while dragging. When performing a copy operation, indicate a copy operation to the user by using the copy cursor. (See “Standard Cursors” (page 157))

When determining whether to move or copy a dragged item, you must consider the underlying data structure of the contents in the destination window. For example, if your application allows two windows to display thesamedocument(multipleviewsofthesamedata),adrag-and-dropoperationbetweenthesetwowindows should result in a move.

The principle driving these drag-and-drop guidelines is to prevent the user from accidental data loss. Because an Undo command in the destination application does not trigger an Undo in the source application, moving data across applications may result in potential data loss. Moving data within the same window (or same volume, as in the case of the Finder) does not lead to data loss.

Table 9-1 Common drag-and-drop operations and results

Dragged item	Destination	Result
Data in a document	The same document	Move
Data in a document	Another document	Copy
Data in a document	The Finder	Copy (creates a clipping)
Finder icon	An open document window	Copy
Finder icon	The same volume	Move
Finder icon	Another volume	Copy

When to Check the Option Key State

Your application should check whether the Option key is pressed at drop time. This behavior gives the user the flexibility of making the move-or-copy decision at a later point in the drag-and-drop sequence. Pressing the Option key during the drag-and-drop sequence should not “latch” for the remainder of the sequence.

Note: The Option key does not act as a toggle switch; Option-dragging between containers always initiates a copy operation. This guideline helps users learn that Option means copy.

Selection Feedback

This section covers issues that deserve special mention in the context of drag and drop. Selection feedback is discussed in more detail in “Selecting” (page 108)

118	Selection Feedback

2008-06-09 | © 1992, 2001-2003, 2008 Apple Inc. All Rights Reserved.