Java Reference
In-Depth Information
Viewer
SelectionTool
DragTracker
EditPart
1: buttonDown
1.1: getDragTracker
1.2: buttonDown
2: buttonUp
2.1: buttonUp
2.1.1: select part
Figure 9-11
GEF mouse interaction
Closely related to selection is focus. Focus is a single EditPart that the
EditPartViewer maintains. Focus is used when manipulating selection via key-
board. By moving focus, the user can navigate from one EditPart to another
without changing the current selection. The user can add or remove the focused
EditPart from the selection. If focus is not explicitly set, it is the same as the
primary selected part.
Selection Handles
The EditPart is responsible for showing its selected and focused state to the
user. The viewer tells EditPart s when they are selected, when they are focused,
or when they have primary selection. Typically, selection is shown by one or more
EditPolicies adding selection handles. In Figure 9-12, ResizableEditPolicy
added the handles. The black handles on the leftmost connection indicate primary
selection.
Because selection handles are related to how a part can be dragged or sized—
which, in turn, is related to the containing figure's layout manager—usually the
parent part's EditPolicy installs a policy on the children for displaying the
appropriate handles. For example, an XYLayoutEditPolicy would install a
ResizableEditPolicy on each child of its host EditPart .
 
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