读取XML，添加节点

private void btnReadXml_Click(object sender, EventArgs e)
        {
            OpenFileDialog openDia = new OpenFileDialog();
            if (openDia.ShowDialog() == DialogResult.OK)
            {
                string strPath = openDia.FileName;
                
                XmlDocument xmlDoc = new XmlDocument();
                xmlDoc.Load(strPath);
                XmlNodeList nodeList = xmlDoc.DocumentElement.ChildNodes;
                XmlElement newNode = null;
                foreach (XmlNode node in nodeList)
                {
                    if (node.Name == "MBProperty")
                    {
                        foreach (XmlNode li in node.ChildNodes)
                        {
                            if (li.Name == "IIsWebServer")
                            {
                                string s = li.Attributes["ServerComment"].Value;
                                if (s.Equals(txtValue.Text))
                                {
                                    newNode = xmlDoc.CreateElement(txtNode.Text);
                                    newNode.SetAttribute(txtMsg1.Text, txtValue1.Text);
                                    li.AppendChild(newNode);//想把这个newNode添加在当前li节点之后 
                                }
                            }
                        }
                    }
                }
                string fileName = DateTime.Now.ToString("yyyyMMddhhmmss") + ".xml";
                XmlTextWriter writer = new XmlTextWriter(fileName, null);
                writer.Formatting = Formatting.Indented;
                xmlDoc.WriteTo(writer);
                writer.Close();

            }
        }