[glade--]Newbie question : how to access a contained object ?

Hello,

I am trying to learn the basics of GTKmm and Glade.

I have designed a very simple Window with 1 button and a text
field (Gtk::Entry). I have setup call-backs for the button.

I would like to display some text in the text field
when I click on the button. The problem I have is that Glademm
generates the pointer to the text field as a local variable of the
constructor of my window; hence, I don't know how to get a pointer
of the text area when my call-back is triggered.

If I use Glade C code generator, I can manage to get a pointer on
the text area using lookup_widget() passing it the name of my text
area; but, with the C++ code generator, I am stuck.

Any idea ?

TIA.