A Form View Update Event Args object is passed to the event-handling method, which allows you to determine the value of an optional command argument sent to the Form View control and to indicate that the update operation should be canceled.The command argument value corresponds to the Command Argument property of the Update button.To cancel the update operation, set the collections, if necessary, before the values are passed to the data source.A common way to use these collections is to HTML-encode the values supplied by the user before they are stored in the data source. For more information about handling events, see NIB: Consuming Events. If it's bound via Linq Data Source, Sql Data Source or Object Data Source I suggest you have a look at the Updating Event.
Because Item Updated is asynchronous, the user may not see their new values when they see the list after submitting the edit.
You can also use event receivers to validate the data that the user wants to change.
This walkthrough is based on the first one where I have a custom list with planets of our solar system.
This allows you to provide an event handler that performs a custom routine, such as canceling the update operation, whenever this event occurs.
A Details View Update Event Args object is passed to the event handler, which allows you to determine the index of the record being updated and to indicate that the update operation should be canceled.
event when an Update button (a button with its Command Name property set to "Update") within the control is clicked, but before the Form View control updates the record.