C# 按照DataSet格式 写入 XML 文件

    string fileName = "xml" + System.DateTime.Now.ToString().Replace(":","") + ".xml";
    System.IO.FileStream fs = new System.IO.FileStream(fileName, System.IO.FileMode.Create);
    System.Xml.XmlTextWriter xtw = new System.Xml.XmlTextWriter(fs, System.Text.Encoding.Unicode);
    xtw.WriteProcessingInstruction("xml", "version='1.0'");

    xtw.WriteStartElement("DEC_DATAS");
    xtw.WriteEndElement();   
    //添加root，否则报错
    xtw.Close();

    //先建立一个XML DOM
    XmlDocument doc = new XmlDocument();

    //读入XML文件
    doc.Load(fileName);
    XmlElement decDataElement = doc.CreateElement("DEC_DATA");      //-----------------------------------------------------------------1

    foreach(DataTable dt in objDataset.Tables)
    { 
     foreach(DataRow dr in dt.Rows)
     {    
      XmlElement tableElement = doc.CreateElement(dt.TableName);      //-------------------------------------------------------------------2
      foreach(DataColumn dc in dt.Columns)
      {
       XmlElement colElement = doc.CreateElement(dc.ColumnName);   //---------------------------------------------------------------------3
       colElement.InnerText = dr[dc].ToString();
       tableElement.AppendChild(colElement);
      }
      decDataElement.AppendChild(tableElement);
     }
    }

    doc.DocumentElement.AppendChild(decDataElement);
    doc.Save(fileName);