How to render Java elements in a tree or table viewer

How to present Java elements in a standard JFace viewer

The JDT-UI API provides several classes to present the Java model or parts of it in a standard JFace viewer. This functionality is provided primarily by:

StandardJavaElementContentProvider which translates the Java element hierarchy into a data structure accessible by a tree, table or list viewer
JavaElementLabelProvider which provides corresponding images and labels for a standard JFace viewer

Putting the pieces together is quite simple:

	...
	IJavaProject jProject= ...;

	TreeViewer viewer= new TreeViewer(parent); 
	// Provide members of a compilation unit or class file, but no working copy elements
	ITreeContentProvider contentProvider= new StandardJavaElementContentProvider(true, false);
	viewer.setContentProvider(contentProvider);
	// There are more flags defined in class JavaElementLabelProvider
	ILabelProvider labelProvider= new JavaElementLabelProvider(
		JavaElementLabelProvider.SHOW_DEFAULT | 
		JavaElementLabelProvider.SHOW_QUALIFIED | 
		JavaElementLabelProvider.SHOW_ROOT);
	viewer.setLabelProvider(labelProvider);
	
	// Using the Java model as the viewers input present Java projects on the first level.
	viewer.setInput(JavaCore.create(ResourcesPlugin.getWorkspace().getRoot()));
	...

In addition to the Java model the StandardJavaElementContentProvider class supports the following input element types: IJavaProject, IPackageFragmentRoot, IPackageFragment and IFolder.

Adding problem and override decorators

When a viewer is supposed to include problem annotations, then a DecoratingLabelProvider together with the ProblemsLabelDecorator is used. Below is a code snippet that outlines the use of a problem label decorator:

	...
	DecoratingLabelProvider decorator= new DecoratingLabelProvider(labelProvider, new ProblemsLabelDecorator());	
	viewer.setLabelProvider(decorator);
	...

In the same way the OverrideIndicatorLabelDecorator can be used to decorate a normal label provider to show the implement and override indicators for methods.

Updating the presentation on model changes

Neither the OverrideIndicatorLabelDecorator nor the

 
ProblemsLabelDecorator

listen to model changes. Hence, the viewer doesn't update its presentation if the Java or resource marker model changes. The reason for pushing the update onto the client for these classes is that there isn't yet a generic implementation that fulfills all performance concerns. Handling Java model delta inspection and viewer refreshing in each label decorator or provider would lead to multiple delta inspections and unnecessary viewer updates.

So what does the client need to do in order to update their viewers ?

OverrideIndicatorLabelDecorator: the client must listen to Java model changes (see JavaCore.addElementChangedListener ) and decide if the change(s) described by the delta invalidates the override indicator of elements presented in the viewer. If so, the class inspecting the delta should trigger a repaint of the corresponding Java elements using the standard JFace viewer API (see update methods on StructuredViewer).
ProblemsLabelDecorator: the client should listen to changes notified by the decorator via a ProblemsLabelChangedEvent (see also ProblemsLabelDecorator.addListener ). Since the marker model is resource based, the listener has to map the resource notifications to its underlying data model. For an example showing how to do this for viewers presenting Java elements see the internal classes ProblemTreeViewer.handleLabelProviderChanged.

For the same reasons enumerated for label decorators the StandardJavaElementContentProvider doesn't listen to model changes. If the viewer needs to update its presentation according to Java model changes, then the client should add a corresponding listener to JavaCore. If the change described by the delta invalidates the structure of the elements presented in the viewer then the client should update the viewer using the standard JFace API (see refresh methods on StructuredViewer, and the add and remove methods on TableViewer and AbstractTreeViewer).