Get attribute values from matching XML nodes using XPath query

Question

This doesn't seem like it should be difficult, but I'm stuck currently. I'm trying to get the attribute values for a particular attribute from nodes that match a given XPath query string. Here's what I have so far:

    public static IEnumerable<string> GetAttributes(this XmlDocument xml,
        string xpathQuery, string attributeName)
    {
        var doc = new XPathDocument(new XmlNodeReader(xml));
        XPathNavigator nav = doc.CreateNavigator();
        XPathExpression expr = nav.Compile(xpathQuery);
        XPathNodeIterator iterator = nav.Select(expr);
        while (iterator.MoveNext())
        {
            XPathNavigator curNav = iterator.Current;
            if (curNav.HasAttributes)
            {
                XmlNode curNode = ((IHasXmlNode)curNav).GetNode();
                if (null != curNode)
                {
                    XmlAttribute attrib = curNode.Attributes[attributeName];
                    if (null != attrib)
                    {
                        yield return attrib.Value;
                    }
                }
            }
        }
    }

This currently throws an exception:

System.InvalidCastException: Unable to cast object of type 'MS.Internal.Xml.Cache.XPathDocumentNavigator' to type 'System.Xml.IHasXmlNode'.

Am I going about this wrong? Is there a simpler way to get attribute values from matching nodes?

Answer 1

For the following xml:

<root>
  <elem att='the value' />
</root>

You can get the "the value" text with this C# code

    XmlDocument xdoc = new XmlDocument();
    xdoc.LoadXml(text);
    Console.WriteLine(xdoc.SelectSingleNode("/root/elem/@att").Value);