34 C# XmlDocument class

Reading XML with the XmlDocument class

As described in the previous chapter, the XmlDocument is more memory consuming and possibly a bit slower than the XmlReader approach. However, for many purposes, the XmlDocument can be easier to work with and often require less code. Once the XML content has been read, you can read the data in a hierarchical way, just like the XML structure, with a root element which can have child elements, which can have child elements, and so on. In the previous chapter, we parsed XML data from the European Central Bank which could tell us about the current currency exchange rates, and we will do the same now, but using the XmlDocument class instead. 

The XML can be found at the current URL (http://www.ecb.int/stats/eurofxref/eurofxref-daily.xml) and the data we need is in the <Cube> elements. In a tree structure, it looks something like this:

<gesmes:Envelope>
    [other child nodes]
    <Cube>
        <Cube time="2011-04-12">
            <Cube currency="USD" rate="1.4470"/>
            <Cube currency="JPY" rate="121.87"/>
            …

The gesmes:Envelope is our root element, which we can access using the DocumentElement property. We will then be able to access children of this node by using the ChildNodes collection property. In our example, we want the child nodes three levels below the root/document element. We can do that using the following code, which essentially does the same as the XmlReader based code in the previous chapter:

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

namespace ParsingXml
{
    class Program
    {
        static void Main(string[] args)
        {
            XmlDocument xmlDoc = new XmlDocument();
            xmlDoc.Load("http://www.ecb.int/stats/eurofxref/eurofxref-daily.xml");
            foreach(XmlNode xmlNode in xmlDoc.DocumentElement.ChildNodes[2].ChildNodes[0].ChildNodes)
                Console.WriteLine(xmlNode.Attributes["currency"].Value + ": " + xmlNode.Attributes["rate"].Value);
            Console.ReadKey();
        }
    }
}

As you can see, we access the Cube nodes by going down the ChildNodes hierarchy. From the DocumentElement (the root element), we ask for the third child node (zero-index based), then we ask for the first child node of that, and then we ask for the entire collection of child nodes. Obviously this is only possible because we know the structure of the XML document, and it's definitely not very flexible, pretty or easy to change later on. However, the way you navigate an XML document very much depends on the XML source and the data you need. For this example, the above will work just fine and even with a very limited amount of code, but for other purposes, you may want to use a bit more code to increase the readability. 

Once we have a node with a currency rate, we access the two properties we're intersted in and then output them to the console, just like the example in the previous chapter.