public class CommonAdapterFactory implements IAdapterFactory {

	private final IWorkbenchAdapter listAdapter = new IWorkbenchAdapter() {

		@Override
		public Object[] getChildren(final Object o) {
			return ((List<?>)o).toArray();
		}

		@Override
		public ImageDescriptor getImageDescriptor(final Object object) {
			return null;
		}

		@Override
		public String getLabel(final Object o) {
			return null;
		}

		@Override
		public Object getParent(final Object o) {
			return null;
		}
	};

	@SuppressWarnings("rawtypes")
	@Override
	public Object getAdapter(final Object adaptableObject, final Class adapterType) {

		if (adapterType == IWorkbenchAdapter.class && adaptableObject instanceof List<?>) {
			return listAdapter;
		}

		return null;
	}

	@SuppressWarnings("rawtypes")
	@Override
	public Class[] getAdapterList() {
		return new Class[] { IWorkbenchAdapter.class };
	}

}

public class ViewCategories extends ViewPart implements CategorieListener {

	public static final String ID = "GestionComptes-Plugin.ViewCategories";
	TreeViewer viewer = null;

	@Override
	public void createPartControl(final Composite parent) {
		viewer = new TreeViewer(parent);
		getSite().setSelectionProvider(viewer);
		viewer.setLabelProvider(new WorkbenchLabelProvider());
		viewer.setContentProvider(new BaseWorkbenchContentProvider());
		viewer.setInput(CategorieService.INSTANCE.getCategorie());
		CategorieListenerManager.addListener(this);
	}

//...

}