<asp:DropDownList ID="lstCategoriesNews" runat="server" SelectMethod="GetCategoriesNews" DataTextField="Name" DataValueField="Id"></asp:DropDownList>

 protected void ListViewMain_ItemUpdating(object sender, ListViewUpdateEventArgs e)
        {
            Int32 idx = e.ItemIndex;
            System.Web.UI.WebControls.DropDownList idC = (DropDownList)ListViewMain.Items[idx].FindControl("lstCategoriesNews");
            //idC.SelectedIndex - это значение выбора в списке категорий
            ListItem str = idC.Items[idC.SelectedIndex];
            idCategoryNews = Int32.Parse(str.Value);
        }

  protected void ListViewMain_ItemEditing(object sender, ListViewEditEventArgs e)
        {
            Int32 idx = e.NewEditIndex;
            System.Web.UI.WebControls.DropDownList idC = (DropDownList)ListViewMain.Items[idx].FindControl("lstCategoriesNews");
   
        }