changing properties in a Treemodel in a Combobox

[Carlos Pereira <jose carlos pereira ist utl pt>]

Hullo,

Is there a way to easily change a property in a GtkTreeModel,
when something else changes in the interface?

I need to disable/enable specific rows (change the sensitivity) in a 
GtkComboBox, depending on users actions.

gtk-demo shows how to set the sensitivity of a specific row, when the 
tree model is created. To change this sensitivity, the only way I know 
is to create a new renderer, with code as this:

gtk_cell_layout_clear (GTK_CELL_LAYOUT (combo));
renderer = gtk_cell_renderer_text_new ();
gtk_cell_layout_pack_start (GTK_CELL_LAYOUT (combo), renderer, FALSE);
gtk_cell_layout_set_attributes (GTK_CELL_LAYOUT (combo), renderer, 
"text", 0, NULL);
gtk_cell_layout_set_cell_data_func (GTK_CELL_LAYOUT (combo), renderer, 
set_sensitivity, NULL, NULL);

Different functions set_sensitivity, can then be used
to set different sensitivity states for the whole treemodel.

Is this the right way to change properties in a treemodel,
at least in a combobox, or is there a simpler way to achieve
the same thing?

something like this?
gtk_combo_box_set_sensitive (combo, row, state);

Thanks for all your help!
Carlos