validating data in a gridview

Hi!
Is there a way to validate data in a dataview when a user clicks the "update" link?
Is there a way to use custom-validators?
Best Regards,
manfred
I am not sure but try this link for a book like tutorial for gridview control. Hope this helps.
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnaspp/html/GridViewEx.asp