XML 遍历更新重复数据

string filename = AppDomain.CurrentDomain.BaseDirectory + "DefaultStart.xml";
                XmlDocument xmlDoc = new XmlDocument();
                xmlDoc.Load(filename);
                XmlNode xmlNode = xmlDoc.SelectSingleNode("DocumentElement");

                int i = 0;
                if (xmlNode.HasChildNodes)
                {
                    XmlNodeList nodeList = xmlNode.ChildNodes;
                    foreach (XmlNode nd in nodeList)
                    {
                        foreach (XmlNode nd1 in nd)
                        {
                            if (nd1.Name == "Node")
                            {
                                nd1.ChildNodes.Item(1).InnerText = dataGridView1.Rows[i].Cells[1].Value.ToString() ;
                                nd1.ChildNodes.Item(2).InnerText = dataGridView1.Rows[i].Cells[2].Value.ToString();
                                i++;
                            }
                        }
                    }
                }
                xmlDoc.Save("DefaultStart.xml");//保存