dialog box : if no correct input don't close dialog (override run())

["Carmen Alfaro" <perritos_con_frio bluewin ch>]

Hello all,

  I continue writting my first application using gtkmm2.2 (limited to this
version as it's for my school project).

  I'm using an object derive from the FileSelection to specify the name of
a XML file where to store some values.

  What I would like to know is how to prevent the dialog box to exit when
I hit on the OK button.
  
  More precisely when users click the OK button, I need to check that the
name of the file they've entered is valid ( non-empty and with the extension
.xml ). If the values specified aren't correct, I will inform them so with
a MessageDialog and I need the FileSelection box to stay open AFTER they've
responded to the MessageDialog, so they can correct the input. If the input
is right I will call some other method to write this file and hide the dialog.

  I made some extensive reseach on google and this list and found one similar
case, but the solution given isn't very detailed and as a newbie I couldn't
figure out the rest by myself.

http://mail.gnome.org/archives/gtkmm-list/2003-September/msg00246.html
http://mail.gnome.org/archives/gtkmm-list/2003-September/msg00254.html

  Can someone give me a hand with this, please? Thanks in advance.

JC