TreeViewer viewer = TreeViewerFactory.getViewer(); if (viewer != null) viewer.activate();
    public void setContext(Registry ctx)    {        registry = ctx;        EventBus bus = registry.getEventBus();        bus.register(this, ShowProperties.class);        //TODO need to review that code.        TreeViewer viewer = TreeViewerFactory.getViewer();        if (viewer != null) viewer.activate();    }