.net WebService 自定义类型序列化

[Serializable]
public class ItemInfo

{
    public Int64 ItemID;
    public string ItemName;
}

    [WebMethod(Description = "查询物品信息")]
    [SoapHeader("Credentails", Direction = SoapHeaderDirection.InOut)]
    [XmlInclude(typeof(ItemInfo))]
    public ArrayList  QueryItemInfo (string ItemName)
    {
        ArrayList ItemList = new ArrayList();
        try
        {
            Test = new MySqlConnection("");
            Test.Open();
            TestCmd = new MySqlCommand("select * from `item` where name like ?ItemName", Test);

            MySqlParameter PaName = new MySqlParameter("?ItemName", MySqlDbType.VarChar, 255);
            PaName.Value = "%" + ItemName + "%";
            TestCmd.Parameters.Add(PaName);
            TestReader = TestCmd.ExecuteReader();
        }
        catch (MySqlException ex)
        {
            EventLog.WriteEntry("QueryItemInfo", "QueryItemInfo:\n\t" + ex.Message);
        }
        finally
        {
            if (Test.State == ConnectionState.Open)
            {
                if (TestReader.HasRows)
                {
                    while (TestReader.Read())
                    {
                        ItemInfo item = new ItemInfo();
                        item.ItemID = (Int64)TestReader.GetValue(0);
                        item.ItemName = (string)TestReader.GetValue(3);
                        ItemList.Add(item);
                    }
                }
                TestReader.Close();
                Test.Close();
            }
        }
        return ItemList;
    }    
}