Developing a DSL Graphical Notation - Eclipse Modeling Project: A Domain-Specific Language Toolkit - page 139

Navigator and Outline

The Project Explorer view in the Resource perspective enables us to drill down
into our . requirements file and navigate its contents. However, if we attempt
to do this, we'll get ClassCastException s in the error log because we have a
diagram contents contribution to the navigatorContent extension-point that
doesn't know how to handle domain model elements. To fix this issue, we sim-
ply set the activeByDefault property of this contribution to false , as shown
in Figure 4-25. More is involved in making the navigator truly useful, but this at
least avoids the exceptions.

Figure 4-25 Requirements navigator extension

Our selection trees in the editor and the Outline view both show diagram
content. Later we'll want to fix the Outline view so that it again gives us the
“bird's-eye” view of the diagram when the diagram page is selected, but for now
we just filter diagram content from our tree viewers. The process is the same for
both, so we only show the changes made to SelectionTreeEditorPart.
createPartControl() here. The same change needs to be made to
RequirementsEditor.getContentOutlinePage() . As shown here, it's sim-
ply a matter of adding a ViewerFilter that excludes instances of Diagram
from the view (changes in bold).

@Override
public void createPartControl(Composite parent) {
viewer = new TreeViewer(parent, SWT.MULTI);