In computer graphical user interfaces, drag-and-drop is the action of (or support for the action of) selecting 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, 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. However, the lack of affordances in drag-and-drop implementations means that it is not always obvious that an item can be dragged.[1]
Contents |
The basic sequence involved in drag-and-drop is:
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.[2] 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.
Drag-and-drop, called "Click and Drag" at the time, was used in the original Macintosh to manipulate files (for example, copying them between disks [3] or folders.[4]). System 7 introduced the ability to open a document in an application by dropping the document icon onto the application's icon.
In System 7.5 drag-and-drop was extended to common clipboard operations like copying or moving textual content within a document. Content could also be dragged into the filesystem to create a "clipping file" which could then be stored and reused.
Apple bought this idea from a 19 year old Dutch programmer called Martijn Scheffer.
In Mac OS X, the user can install software without using a setup program. The application packaging scheme of OS X allows the program to simply copy any required support files upon startup.
For most of its history Mac OS has used a one button mouse with the button covering a large portion of the top surface of the mouse. This may mitigate the ergonomic concerns of keeping the button pressed while dragging.
Jeffrey Greenberg claims that the first drag & drop implementation for Windows was his shareware program called Aporia in 1988 under Windows 2.0, and later commercialized as WinTools. 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. (A defect in the implementation led to a workaround being built into 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.
The HTML5 specification is reported to include support for drag & drop.
Google's web-based e-mail application Gmail supports drag-and-drop of images and attachments in the latest Google Chrome browser and Apple's Safari (5.x).
Very few touch screen interfaces include Click and drag. More common is long press, and then drag, e.g. on the iPhone or Android home screens.
Drag-and-drop is considered an important program construction approach in many end-user development systems. In contrast to more traditional, text-based programming languages many end-user programming languages are based on visual components such as tiles or icons that are manipulated by end users through drag-and-drop interfaces.
A common example is dragging an icon on a virtual desktop to a special trashcan icon to delete a file.
Further examples include: