In computer graphical user interfaces, drag and drop is a pointing device gesture in which the user selects a virtual object by "grabbing" it and dragging it to a different location or onto another virtual object. In general, it can be used to invoke many kinds of actions, or create various types of associations between two abstract objects.
As a feature, drag-and-drop support is not found in all software, though it is sometimes a fast and easy-to-learn technique. However, it is not always clear to users that an item can be dragged and dropped, or what is the command performed by the drag and drop, which can decrease usability.〔Jakob Nielsen, "Top-10 Application-Design Mistakes," http://www.useit.com/alertbox/application-mistakes.html (19 February 2008).〕
== Actions ==
The basic sequence involved in drag and drop is:
* Move the pointer to the object
* Press, and hold down, the button on the mouse or other pointing device, to "grab" the object
* "Drag" the object to the desired location by moving the pointer to this one
* "Drop" the object by releasing the button
Dragging requires more physical effort than moving the same pointing device without holding down any buttons. Because of this, a user cannot move as quickly and precisely while dragging (see Fitts' law). However, drag-and-drop operations have the advantage of thoughtfully chunking together two operands (the object to drag, and the drop location) into a single action.
Extended dragging and dropping (as in graphic design) can stress the mousing hand.
A design problem appears when the same button selects and drags items. Imprecise movement can cause a dragging when the user just wants to select.
Another problem is that the target of the dropping can be hidden under other objects. The user would have to stop the dragging, make both the source and the target visible and start again. In classic Mac OS the top-of-screen menu bar served as a universal "drag cancel" target. This issue has been dealt with in Mac OS X with the introduction of Exposé.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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