drag and drop

In computer graphical user interfaces, drag-and-drop is the action of (or support for the action of) clicking on a virtual object 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, support for drag-and-drop is not found in all software, though it is sometimes a fast and easy-to-learn technique for users to perform tasks.

Actions

The basic sequence involved in drag-and-drop is:

• Press, and hold down, the button on the mouse or other pointing device, to "grab" the object,
• "Drag" the object/cursor/pointing device to the desired location,
• "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 ^[1]. 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 want 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. This issue has been dealt with in Mac OS X with the introduction of Exposé.

History

The first drag & drop implementation for Windows was a shareware program called Aporia by Jeffrey Greenberg in 1988 under Windows 2.0, and later commercialized as WinTools. This program elaborated the single icon on the Macintosh that supported drag & drop, the trash icon. In Aporia/WinTools all icons had functions that could be obtained by double clicking the left mouse button, by clicking on the right mouse button, or by dragging onto one of several functional icons, such as printing, copying, viewing, and other actions. If an icon was double-clicked on and ran a program, the icon changed to indicate that a program was running, and if it was then dragged to the trash, the program was exited. (factoid: A defect in the implementation lead to a workaround of the Windows operating system Aporia Bits)

Subsequently numerous other competitors provided drag & drop desktop replacements to the standard Windows interface including the Norton Desktop, Xerox, NewWave, and Central Point. In Windows 95, Microsoft prevented developers from taking over the desktop and released a drag & drop model of their own.

The Workplace Shell of OS/2 uses dragging and dropping extensively with the secondary mouse button, leaving the primary one for selection and clicking. Its use like that of other advanced Common User Access features distinguished native OS/2 applications from platform-independent ports.

Examples

A common example is dragging an icon on a virtual desktop to a special trashcan icon to delete a file.

Further examples include:

• Dragging a data file onto a program icon or special window for viewing or processing,
• Moving or copying files to a new location/directory/folder,
• Adding objects to a list of objects to be processed,
• Rearranging widgets in a graphical user interface to customize their layout,
• Dragging a command onto an object to which the command is to be applied,
  • e.g. dragging a color onto a graphical object to change its color,
• Dragging a tool to a canvas location to apply the tool at that location,
• Creating a hyperlink from one location or word to another location or document.
• Some editors like Visual Studio allow dragging selected text from one point to another.

Footnotes

1. ^ Buxton, W. (1986). "Chunking and Phrasing and the Design of Human-Computer Dialogues". Proceedings of the IFIP World Computer Congress: 475-480. 

See also

• Mouse gesture
• point-and-click

External links

• The Interaction-Design.org Encyclopedia entry on Interaction Styles, comparing Direct Manipulation with other Interaction Styles
• DnD in the Apple HIG
• AJAX Drag-and-Drop Demo
• Universal Drag and Drop: drag and drop on internet scale

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