Gtk::ComboBox filtering

hi ,
i’m using Gtk::ComboBox, becouse it’s model-view pattern based,
but i couldn’t find it’s facility when the user types a text into the
combo, that filters it’s entries.
so i begun to write it for my class using Gtk::TreeModelFilter, it works
well, except that it accepts keys only when it’s popup is closed.
i use signal_connect(‘key-press-event’) on the combobox to update my
string for data filtering.
my question is: how can i cach the keys typed into the combobox’s popup