Occurs when a row's Select button is clicked, but before the System.Web.UI.WebControls.GridView control handles the select operation.
The GridView.SelectedIndexChanging event is raised when a row's Select button is clicked, but before the System.Web.UI.WebControls.GridView control handles the select operation. This enables you to provide an event-handling method that performs a custom routine, such as canceling the selection operation, whenever this event occurs.
This event is not raised when you programmatically set the GridView.SelectedIndex property.
A System.Web.UI.WebControls.GridViewSelectEventArgs object is passed to the event-handling method, which enables you to determine the index of the row selected by the user and to indicate that the selection operation should be canceled. To cancel the selection operation, set the System.ComponentModel.CancelEventArgs.Cancel property of the System.Web.UI.WebControls.GridViewSelectEventArgs object to true.
For more information about handling events, see Consuming Events.