Java Swing, 2nd Edition

The Drag API

Once you recognize a drag gesture, you can start an actual drag. The drag source receives many of the same types of events as the drop target. Like a drop target, a drag source has a native peer in the form of a DragSourceContext and receives events as the user drags his object over the source and finally drops it on a drop target. As shown in Figure 24-5, the class diagram for the Drag API is similar to that of the Drop API.

Figure 24-5. Class diagram of DnD’s drag side

The DragSource Class

The DragSource class, the flip side of DropTarget, provides support for creating draggable information. Recall from the beginning of this chapter that unlike the DropTarget class, a regular GUI component is not used as a base. Rather, the base component for starting a drag is encapsulated in the DragGestureRecognizer. The recognizer can in turn start a drag for the DragSource. The DragSource class encompasses the context of the drag and provides a focal point for maintaining the visual state of the drag. For example, several predefined cursors that you can use during the drag operation are built into this class.

Properties

The DragSource class has only three properties, two of which are static and apply to the overall DnD system. These properties are shown in Table 24-14.

Table 24-14. DragSource properties

Property	Data type	get	is	set	Default value
defaultDragSources	DragSource	·
dragImageSupported ...