Drag Icons

When users select and manipulate icons using drag and drop, they expect the graphic icon that represents the item being dragged to remain consistent from the selection through the drag and drop. If the user selects a message icon in the File Manager and starts to drag it, the source portion of the drag icon is represented by that message icon. Providing this kind of consistency makes drag and drop more predictable to the user. Where the destination application uses icons, the icon shown should, in most cases, be the same one that was selected and then dragged and dropped. This behavior is not, however, always appropriate for all applications. Dragging text is an exception. A text drag icon is used instead of dragging the selected text.

Both the source and destination applications specify the visual appearance of drag icons. You are responsible for ensuring that an application has a consistent and appropriate icon to drag. Although the drag-and-drop library provides default icons, it is a good idea for you to specify your own for each application. Most often, you should use the data-typing database to obtain the icon associated with the type data represented by the icon. See Chapter 9, Accessing the Data-Typing Database.

When users start a drag without selecting an icon, it is appropriate for you to provide a relevant drag icon. For example, in an appointment editor, the user can select an appointment out of a scrolling list--which may or may not show icons. You should use an appointment icon as the source indicator. The destination application (for example, a File Manager) should display the same appointment icon.

Parts of the Drag Icon

The drag icon changes appearance to provide drag-over feedback when the user moves it over potential drop zones.

The drag icon has three parts that combine to provide the drag-over feedback:

• A state indicator

• An operation indicator

• A source indicator

The state indicator is a pointer used for positioning combined with a valid or invalid drop zone indicator. The valid state indicator is an arrow pointer. The pointer has a hot spot so users can position it in a predictable manner. The invalid state indicator--a circle with a diagonal line--is displayed when users have positioned the cursor over an invalid drop zone.

The operation indicator gives users feedback on what operation is occurring during the drag; either move, copy, or link. Because most drags are moves, users are given additional feedback when they perform the less-frequent copy or link operations.

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Note -

The operation feedback is drawn on top of the state and source feedback. This behavior is consistent with Motif drag-and-drop behavior.

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The user can choose the drag operation move, copy, or link by pressing and holding certain keys during a drag, as shown in Table 5-1.

Table 5-1 Keys Used to Modify a Drag Operation

Modifier Key	Operation
Shift	Move
Control	Copy
Control and Shift	Link

The source application can force a copy, as in the case of the read-only File Manager window. When the user chooses an operation, the drop zone must match that operation for the drop to succeed; otherwise, the drop zone is invalid. In other words, if the user chooses a copy by holding down the Control key, and then drags the drag icon over the trash icon, the drag icon should show the trash icon as an invalid drop zone and any drop should fail, because copying to the trash is not allowed.

The source indicator represents the selection (or the item being dragged). The source indicator varies depending on whether the selection represents single or multiple items and what kind of item the selection represents.