Questions on Combo inside TreeView

[Leandro Fanzone <leandro hasar com>]

Hello. I'm using Gtk::CellRendererCombo to provide a combobox inside a 
TreeView. I have two questions:

1) The Combo is built from a TreeModel. The field selected with 
property_text_column() is the one to be shown in the combo. How to 
access the other columns for the selected item in the TreeModel? I mean, 
if one item is selected, how to access the values entered in the other 
fields for that item, without having to go through all the children 
comparing strings?
2) If I use property_has_entry() = true, it appears an entry I can edit, 
and a list I can choose from. If that property is false, then there's no 
entry, and the list is visible only while I'm pressing the mouse button. 
Now, how can I have a drop down list (that stays on while browsing it 
without having to hold the mouse button), but without letting the user 
edit a value that is not in the list?

Thank you very much,

Leandro.