How to insert XML child node programmatically

Question

I have what seems to be a simple problem for which I can't find a simple answer.

I have an XML file something like this:

<root>
<firstLevel>
  <parent>
   <child>first child</child>
   <child>second child</child>
   <child>third child</child>
   <child>fourth child</child>
  </parent>
</firstLevel>
</root>

I would like to write a small C# snippet that will allow me to insert a new child node as the first node in the parent (or maybe insert it at any point within the parent) so that I now have

<root>
<firstLevel>
  <parent>
   <child>new child</child>
   <child>first child</child>
   <child>second child</child>
   <child>third child</child>
   <child>fourth child</child>
  </parent>
</firstLevel>
</root>

I've tried using the .InsertBefore method of a node, but I keep getting an error with the second parameter (XmlNode refChild) that my reference is not a child of this node.

Thanks in advance.

Mirko Meier · Answer

Hi Andrew I have modified my example as follows: XmlDocument document = new XmlDocument(); document.Load( filename ); XmlElement childElement = document.CreateElement( NewChild ); XmlNode parentNode = document.SelectSingleNode( root/firstLevel/parent ); parentNode.InsertBefore(childElement parentNode.FirstChild); In your App you added the node to the document and not to the ParentNode. Every XMLDocument allow only ONE Document Element.

trilok nandan sharma · Answer

XmlDocument document = new XmlDocument(); document.Load(Server.MapPath(~/xml/WriteBlogs.xml)); int Row_ID = 1; XmlNode xmlnode = document.SelectSingleNode(//blogfield//entry[@Blog_ID= + Row_ID + ]); XmlElement childElement = document.CreateElement(Comments); childElement.InnerText = New Comment; XmlNode newChild = (XmlNode)childElement; var X=document.GetElementsByTagName(entry)[0]; childElement.SetAttribute(Comment_ID Server.HtmlEncode(1)); childElement.SetAttribute(BlogComment Server.HtmlEncode(txtPostComment.Text.Trim())); childElement.SetAttribute(DateComment Server.HtmlEncode(System.DateTime.Now.ToString())); var p= X.AppendChild(childElement); xmlnode.InsertAfter(childElementp); document.Save(Server.MapPath(~/xml/WriteBlogs.xml)); lblError.Text = Comment Posted Successfully;

Andrew · Answer

Mirko - Thanks. That worked with a few minor modifications (in red ) - otherwise it inserts an empty child node: XmlDocument document = new XmlDocument(); document.Load( filename ); XmlElement childElement = document.CreateElement(  child  ); childElement.InnerText = new child; XmlNode parentNode = document.SelectSingleNode (root/firstLevel/parent); parentNode.InsertBefore(childElement parentNode.FirstChild); --Andrew

Andrew · Answer

Vimal - Not really sure what you are referencing. What is newchild? Do I add it to the code from above? So far I have XmlDocument document = new XmlDocument (); document.Load(filename); XmlElement childElement = document.CreateElement( child ); childElement.InnerText = new child ; XmlNode newChild = ( XmlNode )childElement; XmlNode parentNode = document.SelectSingleNode( root/firstLevel/parent ); //parentNode.AppendChild(childElement); XmlElement ch = ( XmlElement )document.GetElementsByTagName( Child )[0]; document.InsertBefore(newChild ch); but I get an InvalidOperationException on the InsertBefore statement because  This document already has a 'DocumentElement' node.

Vimal Kandasamy · Answer

Hi do you want to insert the child before first element?...then XmlDocument tdoc = new XmlDocument(); tdoc.Load(filename); XmlElement ch = (XmlElement)tdoc.GetElementsByTagName(Child)[0]; after that use tdoc.InsertBefore(newchildch); it will insert new child before 1st element. try this...

Andrew · Answer

Thanks. I had to add a statement childElement.InnerText = new child; But unfortunately this does not give me what I need. It puts the new child as the last child in parent; I need it as the FIRST item in parent as shown in my original example. How do I get it to the first child?

Mirko Meier · Answer

To add a nodethe following code is a solution. The 'filename' ist the path to your xmlFile. XmlDocument document = new XmlDocument(); document.Load(filename); XmlElement childElement = document.CreateElement(child); XmlNode parentNode = document.SelectSingleNode(root/firstLevel/parent); parentNode.AppendChild(childElement);