This event fires in bound mode when the grid contains unbound columns. Unbound columns are columns that have the Name property set to values that do not map to columns in the data source. The information in unbound columns must be provided by the application using the GetUnboundValue event.

In most cases, unbound columns are read-only, and you don't need to handle this event. However, if a value is assigned to an unbound cell, either through editing or programmatically, the grid fires this event to allow the application to store the value using whatever mechanism is appropriate.