Graphical Editing Framework - Eclipse Modeling Project: A Domain-Specific Language Toolkit - page 348

Table 9-5 Moving and Resizing Interactions

Tools Requests Edit Policies and Roles Actions

DragEditPartsTracker ChangeBoundsRequest LayoutEditPolicy AlignmentAction

ResizeTracker AlignmentRequest ResizableEditPolicy MatchSizeAction

REQ_MOVE ContainerEditPolicy

REQ_ADD

REQ_ORPHAN

REQ_CLONE

REQ_ALIGN

REQ_RESIZE

The DragEditPartsTracker extends basic selection behavior so that the
selected parts can be dragged within their graphical viewer. Dragging the selected
parts results in three potential interactions: move, reparent, and clone. All three
use the ChangeBoundsRequest , which extends GroupRequest to include a
size delta, move delta, and mouse location.
While dragging the selection, if the tracker targets the part's original parent,
the request is typed as REQ_MOVE . If the target changes, the interaction becomes
a reparent. For a reparent, a request of type REQ_ORPHAN is sent to the old par-
ent, and the new target is sent a request of type REQ_ADD . Pressing the Ctrl key
(Alt on the Mac) always results in a REQ_CLONE , which is sent only to the target
part.
All these requests are related, in that they require the target to process a rec-
tangle and a mouse location. The LayoutEditPolicy is responsible for han-
dling each of these request types. For layouts that use constraints, each part's
original bounds are taken and modified by the size and move deltas to determine
a new bounds, for which a corresponding constraint is found. For index-based
layouts, the mouse location is used to establish the new index.
A ContainerEditPolicy can optionally contribute additional commands
(not related to the layout) during ADD , ORPHAN , and CLONE requests.

Resizing
Resizing falls under the same category as changing bounds. Note that when resiz-
ing either the top or left sides, the location of the part also changes. Resizing
makes sense only for layouts with constraints, such as XYLayout . The
ResizableEditPolicy adds up to eight resize handles to its host. Clicking the
Selection Tool on one of these resize handles prompts a ResizeTracker to