Because the GridView.SelectedIndexChanging event occurs before the System.Web.UI.WebControls.GridView control performs the select operation, the GridView.SelectedIndex property of the control cannot be used to determine the index of the new row selected by the user. The GridView.SelectedIndex property still contains the index of the previously selected row. To determine the index of the new row selected by the user, use the GridViewSelectEventArgs.NewSelectedIndex property. You can also use this property to programmatically override the row index selected by the user by setting it to another value.