using System;

using System.IO;

using System.Xml;

using System.Xml.XPath;

public class EvaluateSample

{

public static void Main()

{

EvaluateSample myEvaluateSample = new EvaluateSample();

myEvaluateSample.test("books.xml");

}

public void test(String args)

{

try

{

//test Evaluate(String);

XPathDocument myXPathDocument = new XPathDocument(args);

XPathNavigator myXPathNavigator = myXPathDocument.CreateNavigator();

Console.WriteLine(myXPathNavigator.Evaluate("sum(descendant::book/price)"));

//testEvaluate(XPathExpression);

XmlDocument doc = new XmlDocument();

doc.Load("order.xml");

XPathNavigator nav = doc.CreateNavigator();

XPathExpression expr = nav.Compile("sum(//price/text())");

Console.WriteLine(nav.Evaluate(expr));

//testEvaluate(XPathExpression);

XPathNodeIterator myXPathNodeIterator = nav.Select("descendant::book/title");

expr = nav.Compile("sum(//price/text())");

Console.WriteLine(nav.Evaluate(expr,myXPathNodeIterator));

}

catch (Exception e)

{

Console.WriteLine ("Exception: {0}", e.ToString());

}

}

}

运行这个程序，结果如下：

30.97

36.9

36.9

我们可以看到，30.97是books.xml中所有price值的总和，而36.9则是order.xml中所有price值的总和。通过XPAH不仅可以快速查找信息，而且还可以对信息进行一些基本的处理。