How to get xpath from an XmlNode instance

Okay, I couldn’t resist having a go at it. It’ll only work for attributes and elements, but hey… what can you expect in 15 minutes 🙂 Likewise there may very well be a cleaner way of doing it.

It is superfluous to include the index on every element (particularly the root one!) but it’s easier than trying to work out whether there’s any ambiguity otherwise.

using System;
using System.Text;
using System.Xml;

class Test
{
    static void Main()
    {
        string xml = @"
<root>
  <foo />
  <foo>
     <bar attr="value"/>
     <bar other="va" />
  </foo>
  <foo><bar /></foo>
</root>";
        XmlDocument doc = new XmlDocument();
        doc.LoadXml(xml);
        XmlNode node = doc.SelectSingleNode("//@attr");
        Console.WriteLine(FindXPath(node));
        Console.WriteLine(doc.SelectSingleNode(FindXPath(node)) == node);
    }

    static string FindXPath(XmlNode node)
    {
        StringBuilder builder = new StringBuilder();
        while (node != null)
        {
            switch (node.NodeType)
            {
                case XmlNodeType.Attribute:
                    builder.Insert(0, "/@" + node.Name);
                    node = ((XmlAttribute) node).OwnerElement;
                    break;
                case XmlNodeType.Element:
                    int index = FindElementIndex((XmlElement) node);
                    builder.Insert(0, "https://stackoverflow.com/" + node.Name + "[" + index + "]");
                    node = node.ParentNode;
                    break;
                case XmlNodeType.Document:
                    return builder.ToString();
                default:
                    throw new ArgumentException("Only elements and attributes are supported");
            }
        }
        throw new ArgumentException("Node was not in a document");
    }

    static int FindElementIndex(XmlElement element)
    {
        XmlNode parentNode = element.ParentNode;
        if (parentNode is XmlDocument)
        {
            return 1;
        }
        XmlElement parent = (XmlElement) parentNode;
        int index = 1;
        foreach (XmlNode candidate in parent.ChildNodes)
        {
            if (candidate is XmlElement && candidate.Name == element.Name)
            {
                if (candidate == element)
                {
                    return index;
                }
                index++;
            }
        }
        throw new ArgumentException("Couldn't find element within parent");
    }
}