在vs2005环境下，三层架构
 数据层
public static DataSet  getValidityByBarcod  （string barcode)
       {            
           SqlConnection conn = new SqlConnection(connstr);
           string sql = string.Format("select Validity from YpNum where BarCode='{0}'", barcode);
           SqlCommand comm = new SqlCommand(sql,conn);     
           SqlDataAdapter ada = new SqlDataAdapter( );            
           ada.SelectCommand = comm ;
           DataSet ds = new DataSet();   
           ada.Fill(ds, "Validity");   
            return ds;  
       }
业务层
   public static DataSet GetValidityByBarcode(string barcode)        
   {            
        return SalesService.getValidityByBarcode(barcode);
    }
表示层
    cmbValidity.DataSource = SalesManager.GetValidityByBarcode(BarCode);
绑定后combobox却显示System.Data.DataRowView