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Chapter 45. New Media > Overloading Without Overload

Overloading Without Overload

Operator overloading, so dear to programmers and computational linguists, can be either useful or abusive when carried to the user interface. Some overloadings are quite reasonable and delight users, others drive them to distraction. Giving the label at the top of a display column the appearance of a control button invites the user to click on it. Popular software often interprets this action as a request to sort the data in sequence by the column whose label is clicked. The control is overloaded, in this case serving as both a passive label and as an active command button. In some contexts, such as the Windows Explorer, the overloading is taken a step further, making the label button a toggle that reverses the sort sequence when clicked a second time. Such overloading can be made more usable through further overloading that provides active feedback, although care must be taken to avoid sending conflicting messages to the user. The column sort controls should not look like drop-down selections or spin buttons, which would convey the wrong affordance. A small triangle in the label can unambiguously inform the user of both the direction of the current sort and the column on which the data is sorted. After an initial exploration, the first-time user has no difficulty understanding and using such a feature.

For another example of effective overloading, many applications include visual interface components to which data items can be dragged and dropped to initiate some particular processing. Common examples of such “drop zones” include printers and trash-can icons on the screen. In some cases, there may be sound reasons to have both a drop zone to which documents might be dragged and a related control button to trigger an operation on already selected data. Some users prefer the drag-and-drop idiom, but others find drag-and-drop tedious and difficult, preferring to select data, then click on a control. Though not universal, a convention employed in some applications is to communicate “drop affordance” by making the “drop zone” look like a shallow depression or well. “Push affordance” is, by standard practice, communicated by a protruding, convex appearance. A single “drop kick” control, consisting of a button-like protrusion in the center of a shallow well, tells the user, “Drag something here or press—your choice.”


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