DataGridView as Pick List

I'm trying to quickly use a DataGridView as a pick list for recipients.  I
include an IsSelected flag in my Contact struct, and use a List<Contact> as
the data source for my grid.  Now, when I click the CheckBox column bound to
IsSelected, I raise an event and the parent form re-builds the actual text
of the To field based on which contacts have IsSelected set.



There seems to be some kind of mismatch in updating, because when I first
show my pick list and select a contact, the event fires but no contacts are
displayed (I suspect because the data source is not yet updated.)  Then,
when I show the pick list again, and DESELECT the same contact, the event
fires and the name is now displayed.



Any quick advice?  I'm not trying to do a major work here, it's just for a
test UI but selecting multiple contacts is essential.