C# 4 and .NET 4

Using XPathnavigators ❘ 919
If the XPathNavigator was created from an XPathDocument, it is read-only. If it is created from an
XmlDocument, the XPathNavigator can be used to edit the document. This can be verified by checking the
CanEdit property. If it is true, you can use one of the Insert methods. InsertBefore and InsertAfter
will create a new node either before or after the current node. The source of the new node can be from an
XmlReader or a string. Optionally, an XmlWriter can be returned and used to write the new node information.
Strongly typed values can be read from the nodes by using the ValueAs properties. Notice that this is
different from XmlReader, which used ReadValue methods.
XPathnodeiterator
XPathNodeIterator can be thought of as the equivalent of a NodeList or a NodeSet in XPath. This object
has two properties and three methods:
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Clone() — Creates a new copy of itself
Count — Number of nodes in the XPathNodeIterator object
Current — Returns an XPathNavigator pointing to the current node
CurrentPosition() — Returns an integer with the current position
MoveNext() — Moves to the next node that matches the XPath expression that created the
XPathNodeIterator
The XPathNodeIterator is returned by the XPathNavigator Select methods. You use it to iterate
over the set of nodes returned by a Select method of the XPathNavigator. Using the MoveNext method
of the XPathNodeIterator does not change the location of the XPathNavigator that created it.
Using Classes from the XPath namespace
The best way to see how these classes are used is to look at some code that iterates through the books.xml
document. This will allow you to see how the navigation works. In order to use the examples, you first add
a reference to the System.Xml.Xsl and System.Xml.XPath namespaces:
using System.Xml.XPath;
using System.Xml.Xsl;
For this example, you use the file booksxpath.xml. It is similar to the books.xml file that you have been
using, except that there are a couple of extra books added. Here’s the form code, which is part of the
XmlSample project:
private void button1_Click(object sender, EventArgs e)
{
//modify to match your path structure
XPathDocument doc = new XPathDocument("books.xml");
//create the XPath navigator
XPathNavigator nav = ((IXPathNavigable)doc).CreateNavigator();
//create the XPathNodeIterator of book nodes
// that have genre attribute value of novel
XPathNodeIterator iter = nav.Select("/bookstore/book[@genre='novel']");
textBox1.Text = "";
while (iter.MoveNext())
{
XPathNodeIterator newIter =
iter.Current.SelectDescendants(XPathNodeType.Element, false);
while (newIter.MoveNext())
{
textBox1.Text += newIter.Current.Name + ": " +
newIter.Current.Value + "\r\n";
}
}
}
code snippet frmNavigator.cs
www.it-ebooks.info