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in itself, and the Drag Manager does not use the Clipboard. Users can take advantage of both the Clipboard and drag and drop without side effects from each other.

A drag-and-drop operation should provide immediate feedback at the significant points: when the data is selected, during the drag, when an appropriate destination is reached, and when the data is dropped. The data that is pasted should be target-specific. For example, if a user drags an Address Book entry to the “To” text field in Mail, only the email address is pasted, not all of the person’s address information.

You should implement Undo for any drag-and-drop operation you enable in your application. If you implement a drag-and-drop operation that is not undoable, display a confirmation dialog before implementing the drop. A confirmation dialog appears, for example, when the user attempts to drop an icon into a write-only drop box on a shared volume, because the user does not have privileges to open the drop box and undo the action.

Drag and Drop Semantics

Move Versus Copy

Your application must determine whether to move or copy a dragged item after it is dropped on a destination. The appropriate behavior depends on the context of the drag-and-drop operation, as described here.

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.

You can’t assume that a window is always a container; you must consider the underlying data structure of the contents in the window. For example, if your application allows two windows to display the same document (multiple views of the same data), a drag-and-drop operation between these two windows should result in a move.

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Apple Computer, Inc. June 2002

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

Table 12-1 Common drag-and-drop operations and results

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 allows users to learn that Option means copy.

Apple Computer, Inc. June 2002