stackComposite.setLayoutData(gd4);
stack = new StackLayout();
stackComposite.setLayout(stack);
// Create the initial unavailable preview.
unavailablePreview = new UnavailablePreview(stackComposite, SWT.NONE);
// Note: It is unclear why the StackLayout must access the Preview's
// group here rather than just the preview. There may be a bug with
// SWT groups/composites/stacklayouts. Within the Preview class,
// delegating setVisible(boolean) to the Preview's group results