C H A P T E R 1 2

Drag and Drop

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 185).

Single-Gesture Selection and Dragging

Because dragging is defined as moving the mouse while the mouse button is held down, a mouse-down event must occur before dragging can take place. A selection may be made as a result of this mouse-down event, just before the user starts dragging. For example, the user can select and drag a folder icon in a single gesture; the user does not have to click the folder icon first, release the mouse button, and then press again to begin dragging the icon. Your application should ensure that implicit selection occurs, when appropriate, when the user starts dragging.

Single-gesture selection and dragging is possible only when the process of selecting an item does not require dragging. Range-selection operations—such as selecting text or dragging a marquee around graphic objects—don’t lend themselves to single-gesture selection and dragging because the range-selection operation itself requires dragging.

Background Selections

When a window containing a highlighted selection becomes inactive, your application should maintain the selection so that users can drag previously selected data from inactive windows to the active window.

Background selections are not required if the dragged item is discrete, such as an icon or graphical object, because implicit selection can occur when an item is dragged. However, items selected only by range-selection operations such as text or a group of icons must have a background selection to allow the user to drag these items out of inactive windows. Whenever an inactive window is made active, the background selection, if any, becomes highlighted as a normal selection.

222Selection Feedback

Apple Computer, Inc. June 2002