<asp:DropDownList ID="DropDownListCatelog" runat="server" 
DataSourceID="DSCatelogItems" DataTextField="ITEMNAME" 
 DataValueField="ITEMNAME">

------解决方案--------------------
winform or wpf?

------解决方案--------------------
C# code

//取选定项值
          DataRowView dr = comboBox1.SelectedItem as DataRowView;
          int mid =(int)dr.Row["id"];
          string str = dr.Row["name"].ToString();

//取ID=1000用
DataTable drw= comboBox1.DataSource as DataTable;
           DataRow[] str = drw.Select("id=1000");
           foreach (var sd in str)
           {
               string str1 = sd["name"].ToString();
           }