创建一个全局变量  

Public double Sumdb;

private void DataGrid1_ItemCreated(object sender, System.Web.UI.WebControls.DataGridItemEventArgs e)

         {            

              ListItemType lit=e.Item.ItemType;

              if(lit==ListItemType.Footer)

              {

                   TableCell tc1=e.Item.Cells[3];

                   TableCell tc2=e.Item.Cells[4];

                   TableCell tc3=e.Item.Cells[5];

                   TableCell tc4=e.Item.Cells[6];

                   Label L_xj=new Label();

                   L_xj.ID="lb_xj";

                   L_xj.Width=30;

       &