Cross-coupling comboboxes

[Rob Pearce <list gtkmm flitspace org uk>]

Hello experts,

I have a GTKmm (2.24) application in which two different windows each 
have a ComboBoxText controlling the same item, so that whenever the user 
makes a selection on one of them, the other one needs to be updated 
accordingly. This is implemented by calling the set_active with the 
result of get_active_row_number.

Because the content of those combo boxes has got rather voluminous, I 
now want to convert them to hierarchical. So the ...Text version is no 
good and I'm using a ComboBox with a TreeStore behind it. The row number 
obviously no longer works, so...

What's the best way to do this?

Thanks,

Rob