How i can write xml node in C#

Question

i want to write text in xml file under tag "Engine" but right now it can write under tag "Service" here is my code

        XmlDocument doc = new XmlDocument();
        doc.Load(filename);
        XmlElement root = doc.DocumentElement;
        XmlNodeList elemList = root.GetElementsByTagName("Engine");
            for (int i = 0; i < elemList.Count; i++)

            {
                XmlNode head = doc.CreateNode(XmlNodeType.Element, "Host", null);
                XmlAttribute na = doc.CreateAttribute("name");
                na.Value = "url";

                XmlNode nodeTitle = doc.CreateElement("Valve");
                XmlAttribute className = doc.CreateAttribute("className");
                className.Value = "org.apache.catalina.valves.AccessLogValve";

                doc.DocumentElement.LastChild.AppendChild(head);
                doc.Save(filename); 
            }

here is xml file

 <Server>
      <Service name="Catalina">
          <Engine name="Catalina" >
            <Host name="localhost">
              <Valve  />
            </Host>
          </Engine>
      </Service>
 </Server>

Answer 1

You are not using Engine elements in your code. You just adding Host elements to the last child of xml root ( Service ). Also keep in mind that if you have several Engine elements, you will append several Host elements with exactly same values.

First of all, I suggest you to use LINQ to XML . Eg adding Host element to first (if any) Engine element looks like:

var xdoc = XDocument.Load(filename);

var engine = xdoc.Root.Descendants("Engine").FirstOrDefault();

if (engine != null)
{
    engine.Add(new XElement("Host", 
        new XAttribute("name", "url"),
        new XElement("Valve",
            new XAttribute("className", "org.apache.catalina.valves.AccessLogValve"))));

    xdoc.Save(filename);
}

For your sample xml result will be

<Server>
  <Service name="Catalina">
    <Engine name="Catalina">
      <Host name="localhost">
        <Valve />
      </Host>
      <Host name="url">
        <Valve className="org.apache.catalina.valves.AccessLogValve" />
      </Host>
    </Engine>
  </Service>
</Server>

If you want to modify each Engine element, then just use loop:

foreach(var engine in xdoc.Root.Descendants("Engine"))
  // add host to engine here

Answer 2

    XmlDocument doc = new XmlDocument();
    doc.Load(filename);
    XmlElement root = doc.DocumentElement;
    XmlNodeList elemList = root.GetElementsByTagName("Engine");
        for (int i = 0; i < elemList.Count; i++)

        {
            XmlNode head = doc.CreateNode(XmlNodeType.Element, "Host", null);
            XmlAttribute na = doc.CreateAttribute("name");
            na.Value = "url";

            // nodeTitle is not appended the document:
            //XmlNode nodeTitle = doc.CreateElement("Valve");
            // className is not appended to any node either:
            //XmlAttribute className = doc.CreateAttribute("className");
            //className.Value = "org.apache.catalina.valves.AccessLogValve";

            // this line will add your node to the last node of your document:  
            //doc.DocumentElement.LastChild.AppendChild(head);
            // if you want to add it to every "Engine" node:
            elemList[i].AppendChild(head);
            //doc.Save(filename); 
        }
        // save at the end, when you're done with the document:
        doc.Save(filename); 

Answer 3

I like XML Linq

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Xml;
using System.Xml.Linq;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            string xml = "<?xml version=\"1.0\" encoding=\"utf-8\" ?><Server><Service name=\"Catalina\">" +
                "<Engine name=\"Catalina\"></Engine>" +
                "<Engine name=\"Catalina\"></Engine>" +
                "<Engine name=\"Catalina\"></Engine>" +
                "</Service></Server>";

            XDocument doc = XDocument.Parse(xml);

            foreach(XElement engine in doc.Descendants("Engine"))
            {
                object[] newNode =  { new XElement("Host", new XAttribute("name", "localhost")), new XElement("Value")};
                engine.Add(newNode);
            }

        }
    }
}