[Qt-interest] Designer: Promote to: my widgets in widget box are not available as base classes

[Giacomo]

Hi to all.
I have my "Label", derived from QLabel and available into the "Widget Box" 
dock widget of my Qt4 designer, because I built a plugin and installed it into 
the designer plugins path.

I can use my Label, but when I want to inherit from it, let's say creating 
class Label2 : public Label
and want to promote Label into Label2 by means of the designer Promote to 
functionality, Label is not available through the list of Base classes.

How can I do it?

Thanks in advance.

Giacomo.