DataGrid: Update data source when closing form

Hi,

The situation is the following: A user is editing a cell in a DataGrid, and
hasn't pressed <return> or <enter>, so the value is being edited. The user
then closes the form. I would like to update the value to the data source if
it is valid, or prevent closing the form if the edited value is invalid.

Actually, all I need for this to accomplish are the following two functions:
(1) A function that tells me whether or not the user is actually editing a
cell's contents.
(2) A function that tries to end the edit operation, and returns whether
ending the operation succeeded. Ending the edit operation should fail if the
value being edited is invalid (not valid).

I haven't found these yet.
About (1): I've checked DataRowView's IsEdit member, but I tested it and it
seems to return true even if a user isn't editing a cell in that row.
About (2) DataGrid has an EndEdit method. Sadly it returns false when no
cell is being edited, so I can't make the distinction between an invalid
entry or the fact that the cell isn't being edited. So using (2) alone
doesn't work.

Thanks for any help
--
Tom Tempelaere.