@Override
    public void saveState(IMemento aMemento) {

        final Object[] expanded = getCommonViewer().getVisibleExpandedElements();

        aMemento = aMemento.createChild("expanded");

        for (int i = 0; i < expanded.length; i++) {
            aMemento.createChild("nodes", expanded[i].toString());
        }

        super.saveState(aMemento);
    }