Newbie question: I don't understand Glade...

I created a form with Glade, I've loaded it and It's shown correcly. How can I access values in the widgets inside the gtkWindow? I tried with this code:

        ...
       $frmAnagrafica=$glAnagrafica->get_widget('frmAnagrafica');     //gtkWindow
       $glAnagrafica->signal_autoconnect_instance($this);
       $frmAnagrafica->txt_ragsoc->set_text('Test'); //class: gtkEntry  name: txt_ragsoc <- without this the form it's shown and the signls are correctly attached...
       ...
I receive the error: Call to a member function set_text() on a non-object in...

Why? The objet tree in the window is: frmAnagrafica | +--vBox1

            |
            +--hBox1
                     |
                     +--txt_ragsoc

Thanks Massimiliano