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Common Desktop Environment: Style Guide and Certification Checklist

Scrolling Lists

In the Common Desktop Environment, items in a scrolling list are text objects by default. They can be buffer objects, but they cannot be both text and buffers. For example, the Calendar Appointment Editor has a scrolling list of appointments that the user can select and drag. When the user drags an appointment, they are manipulating a buffer and the drag icon shows an appointment icon as the source indicator, as shown in Figure 3-7. A Mailer container window has a list of mail messages in the upper portion of the window. Users can select and drag one or more messages from this list. These messages are actually buffers and the drag icon shows a mail message as the source indicator. If multiple mail messages are dragged, then the drag icon shows the multiple source indicator.

Figure 3-7 Example of a scrolling list with an item selected for dragging

Graphic

If your application uses a scrolling list to show mail message headers or list other kinds of objects, then you need to integrate dragging with extended selection. this behavior can be seen in the Mailer application.

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In a collection that uses range selection, pressing BSelect on an unselected element sets an anchor on the element, or at the position where BSelect was pressed, and deselects all elements in the collection. If BSelect is released before the drag threshold has been exceeded, then the element under the pointer should be selected. If BSelect Motion exceeds the drag threshold, then a new selection should begin. The anchor and the current position of the pointer determine the current range. As BSelect is dragged through the collection, the current range is highlighted. When BSelect is released, the anchor does not move, and all the elements within the current range are selected. 

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In a collection that uses range selection, pressing BSelect on an currently selected element should not cause all other elements in the selection set to be deselected. If BSelect is released before the drag threshold is exceeded, then, at that point, all other elements should be deselected and the element under the pointer should remain selected. If BSelect Motion exceeds the drag threshold, then no element should be deselected and a drag operation should begin.