Graphical Editing Framework - Eclipse Modeling Project: A Domain-Specific Language Toolkit - page 350

and then click on two EditPart s that support connections. Note that GMF's
default behavior is a click-drag-release to create a connection. You can abort the
creation by pressing the Esc key. The ConnectionDragCreationTool is simi-
lar, but the interaction is a single mouse drag. This tool can be returned as the
drag tracker from a handle or even an EditPart , in some cases.
The process is separated into two parts. The first part is defining the source
of the connection. The source is a node, but it also can include a specific “port”
on that node. The tool uses a CreateConnectionRequest identified by
REQ_CONNECTION_START to determine the target EditPart and ask it for a
command. However, this is only the first half of creating the connection, so the
command is not complete yet. The tool does not attempt to execute this com-
mand or even ask if it is executable; it only passes information to the target
EditPart .
The second part of the process is to define the target node for the connection.
The tool uses the same request but retypes it as REQ_CONNECTION_END . The
command that the source node returns is now stored on the request and passed
during the second part of the interaction. The target is asked for the final com-
mand that performs the entire creation of the connection. Any command can be
returned at this point, including the command provided upon the request,
updated with the target node information. At this point, enablement is deter-
mined by asking the command if it can be executed. Creation ends by executing
the command.
During the first and second steps, the EditPart being targeted as the source
or target node is asked to show target feedback. The EditPart might visually
highlight various attachment points or simply indicate that it is the target.
The source node EditPart is also asked to show source feedback during
creation. The provided GraphicalNodeEditPolicy can display creation feed-
back. This policy creates a connection feedback figure and sets its anchors using
the NodeEditPart interface. This mix-in interface for GraphicalEditPart
provides anchor points both during creation feedback and when the connection's
EditPart is created.
The “source” and “target” nodes should not be confused with “source” and
“target” feedback. For feedback, source simply means show the feedback for the
connection, and target means highlight the mouse target element.
Editing Connections
Table 9-7 details the elements involved in connection edit interactions.