The rowupdating event
The hashtable contains former values of the row's cells.
If the grid contains templated columns or is bound to some of the fields from the data source, the Values and Old Values must be updated to add those missing values.
If they are not equal, values cannot be assigned to the update command. What happens with this is that the source is being created every time the user submits the page.This means that when the user does an update, the data from that update is lost.event is raised when a row's Update button is clicked, but before the Grid View control updates the row.This enables you to provide an event-handling method that performs a custom routine, such as canceling the update operation, whenever this event occurs.