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