exclamation-mark in ROW-header doesn't disappear

Oct 7, 2010 at 12:23 PM


I use my datagrid to show some telephonenumbers. It is also possible to add e new number and I use the event InitializingNewItem to initialize my number-field (is actually a string):  

             CT_TELNUMBERS rec = e.NewItem as CT_TELNMBERS;
            if (rec != null)
                rec.ID = rec.GetSequence();
                rec.NUMBER = string.Empty;

The datagrid shows this error with:
- an exclamation-mark in the row-header
- a red border around the cell.
O.k. so far.
When I enter the number and leave the field, the red border around the cell disappears, but the exclamation-mark in the row header stays there. 

This error only occurs when I initialize my number-field in case of a new item. I do this, because I want the user to see that this is a mandatory field.
If I change an existing telephone-number to NULL. leave the field (red border and exclamation-mark in header), return to the field and enter an number the red border AND the exclamation-mark disappear.

How can I get the exclamation mark to disappear?