Efficient way to construct an XML document from a string containing well formed XML for navigation?

Question

I have a string that contains well formed xml in it. I want to navigate the XML in that string to extract the text in certain nodes. How do I efficiently accomplish this using a built-in .NET class. Which .NET XML class would you use and why?

Many thanks for your help.

Note 1: Linq is not available to me. Note 2: Editing the XML is not important. Read-only access is what I need.

Answer 1

For speed, use an XmlReader:

using (StringReader sr = new StringReader(myString))
using (XmlReader xr = XmlReader.Create(sr))
{
    while (xr.Read())
    {
        if (xr.NodeType == XmlNodeType.Element && xr.Name == "foo")
        {
            Console.WriteLine(xr.ReadString());
        }
    }
}

The above prints out the text content of every element named "foo" in the XML document. (Well, sort of. ReadString doesn't handle nested elements very gracefully.)

Using an XPathDocument is slower, because the entire document gets parsed before you can start searching it, but it has the merit of simplicity:

using (StringReader sr = new StringReader(myString))
{
    XPathDocument d = new XPathDocument(sr);
    foreach (XPathNavigator n in d.CreateNavigator().Select("//foo/text()"))
    {
        Console.WriteLine(n.Value);
    }
}

If you're not concerned with performance or memory utilization, it's simplest to use an XmlDocument:

XmlDocument d = new XmlDocument();
d.LoadXml(myString);
foreach (XmlNode n in d.SelectNodes("//foo/text()"))
{
   Console.WriteLine(n.Value);
}

Answer 2

For navigation? Probably XPathDocument:

string s = @"<xml/>";
XPathDocument doc = new XPathDocument(new StringReader(s));

From MSDN,

Provides a fast, read-only, in-memory representation of an XML document by using the XPath data model.

Unlike XmlDocument etc, it is optimised for readonly usage; more efficient but less powerful (i.e. you can't edit it). For notes on how to query it, see here.