DataSet 转xml

T_GZUNIT u = new T_GZUNIT();
            u.UNITID = 33333;
            u.CANTONID = 4444;
            u.PHASE = "2011-11";

            T_GZUNIT u1 = new T_GZUNIT();
            u.UNITID = 33333;
            u.CANTONID = 4444;
            u.PHASE = "2011-11";
            T_GZUNIT u2 = new T_GZUNIT();
            u.UNITID = 33333;
            u.CANTONID = 4444;
            u.PHASE = "2011-11";
            T_GZUNIT u3 = new T_GZUNIT();
            u.UNITID = 33333;
            u.CANTONID = 4444;
            u.PHASE = "2011-11";

            List<T_GZUNIT> lst = new List<T_GZUNIT>() { u, u1, u2, u3 };

            DataTable dt = DataConvert.ListToDataTable(lst);
            DataSet ds = new DataSet("UNITINFO");
            dt.TableName = "UNIT";
            ds.Tables.Add(dt);
            StringBuilder sb = new StringBuilder();
            string filename = "myXmlDoc.xml ";
            //   Create   the   FileStream   to   write   with.
            System.IO.FileStream myFileStream = new System.IO.FileStream
                  (filename, System.IO.FileMode.Create);
            System.Xml.XmlTextWriter myXmlWriter =
              new System.Xml.XmlTextWriter(myFileStream, System.Text.Encoding.GetEncoding("UTF-8"));
            myXmlWriter.WriteStartDocument();
            ds.WriteXml(myXmlWriter, XmlWriteMode.IgnoreSchema);

 

  public static DataTable ZeroNullValues(this DataTable dataTable)
        {
            foreach (DataRow row in dataTable.Rows)
            {
                for (int i = 0; i < dataTable.Columns.Count; i++)
                {
                    if (row[i]==System.DBNull.Value)
                    {
                        Type columnType = dataTable.Columns[i].DataType;
                        if (columnType == typeof(string))
                        {
                            row[i] = string.Empty;
                        }
                        else if (columnType == typeof(int) || columnType == typeof(long))
                        {
                            row[i] = 0;
                        }
                        else if (columnType == typeof(float) || columnType == typeof(double))
                        {
                            row[i] = 0.00F;
                        }
                    }
                }
            }
            return dataTable;
        }