signal emitted when CLICKING on a combo box

["Carmen Alfaro" <perritos_con_frio bluewin ch>]

Hello everyone,

  I am writting my first application using gtkmm2.2 ( restricted to this
version because is a school project ).

  I would like to know if someone out there could tell me which is the signal
emitted when I click on the arrow ( the button to the right of the text entry
with the arrow icon ) of a combo box. I need to catch this signal so that
I can query for some data, populate the popdown strings and show the user
the up-to-date data.

  While searching throw this forum I learned how to catch a signal when the
text entry value has changed, but this is not what I need. I need to catch
the signal before the dropdown list is shown, namely because I need to update
that list before showing it.

  Can anyone help me? Thanks in advance.

JC