Graphical Editing Framework - Eclipse Modeling Project: A Domain-Specific Language Toolkit - page 326

Create and maintain a view

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Create and maintain child EditParts

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Create and maintain connection EditParts

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Support editing of the model

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As the controller, EditPart s are responsible for listening to model change
events and updating the view, and also for taking input from a user and updat-
ing the model. We cover both aspects in the following sections, beginning with a
description of how to create the graphical view.

9.2.2 Creating the Graphical View

Let's say that you have a model created in EMF and figures using Draw2d. Now
it's time to bring them together in a graphical editor. As indicated in the previous
section, you need to create EditPart s for each of the model elements you want
to render in a diagram. But first you need to set up a viewer for the Draw2d
FigureCanvas . Typically, the GEF ScrollingGraphicalViewer is used with
a special root EditPart . This root EditPart does not correspond to a model
element; it provides a context for the remaining EditPart s and sets up the
viewer. The ScalableFreeformRootEditPart is typically used, while GMF
provides its own DiagramRootEditPart class to set up printing support and
discrete zoom levels.

Creating EditParts
With a viewer and the root EditPart established, we can populate the view
with content by passing in an EditPartFactory and our model. The
EditPartFactory takes the base model object and creates the appropriate
EditPart and adds it to the root, as seen in Figure 9-9. This EditPart is
known as the contents EditPart ; do not confuse it with the “root EditPart ,”
which, as stated earlier, has no relationship with the model. The contents
EditPart creates its Figure , which is added to the root Figure .
The contents EditPart creates its children EditPart s by passing the
viewer's factory, which, in turn, is used to create their children, and so on. This
is done by calling getModelChildren() on itself, so the EditPart must know
what model elements require EditPart s to be created, although it is the respon-
sibility of the EditPartFactory to create them. Eventually, every model object
will be represented by an EditPart and corresponding Figure in the graphical
viewer. In summary, you need to implement both a contents EditPart that will
set up a diagram's backdrop figure and an EditPartFactory that is aware of
the model and can create the contents EditPart .