使用XPathNavigator和XPathExpression求出XPath的值，[源代码]

假设有如下ＸＭＬ文件：

<?xml version="1.0" encoding="utf-8" ?>
<bookstore>
  <book genre="autobiography" publicationdate="1981-03-22" ISBN="1-861003-11-0">
    <title>The Autobiography of Benjamin Franklin</title>
    <author>
      <first-name>Benjamin</first-name>
      <last-name>Franklin</last-name>
    </author>
    <price>8.99</price>
  </book>
  <book genre="novel" publicationdate="1967-11-17" ISBN="0-201-63361-2">
    <title>The Confidence Man</title>
    <author>
      <first-name>Herman</first-name>
      <last-name>Melville</last-name>
    </author>
    <price>11.99</price>
  </book>
  <book genre="philosophy" publicationdate="1991-02-15" ISBN="1-861001-57-6">
    <title>The Gorgias</title>
    <author>
      <name>Plato</name>
    </author>
    <price>9.99</price>
  </book>
</bookstore>

   需要求出：
1: 所有书的总价，即sum(price)
2:ＩＳＢＮ＝"0-201-63361-2"的书的价格，使用ＸＰａｔｈ可以表达： /bookstore/book[@ISBN="0-201-63361-2"]/price

　简单分析：
XPathNavigator／XPathExpression　是２个很重要的类，顾名思义，XPathNavigator是用来定位的Ｎｏｄｅ上下文的，定位之后，才能求出相对的Ｘｐａｔｈ值。XPathExpression是表达式
　大家看看代码就清楚了：

using System;
using System.Collections.Generic;
using System.Text;
using System.Xml.XPath;
using System.Xml;

namespace XPathNavigatorSample
{
    class Program
    {
        static void Main(string[] args)
        {
            XmlDocument xdoc = new XmlDocument();
            xdoc.Load("books.xml");

            XmlNode xnode = xdoc.SelectSingleNode("/bookstore/book");
            XPathNavigator navigator = xnode.CreateNavigator();

            //XPathExpression query = navigator.Compile("string(sum(price))");
            //Evaluate(query, navigator);

            query = navigator.Compile("string(sum(//price))");
            Evaluate(query, navigator);

            XPathExpression query2 = navigator.Compile("string(//book[@ISBN='0-201-63361-2']/price)");        
            Evaluate(query2, navigator);
        }


        public static void Evaluate(XPathExpression expression, XPathNavigator navigator)
        {
            switch (expression.ReturnType)
            {
                case XPathResultType.Number:
                    Console.WriteLine(navigator.Evaluate(expression));
                    break;

                case XPathResultType.NodeSet:
                    XPathNodeIterator nodes = navigator.Select(expression);
                    while (nodes.MoveNext())
                    {
                        Console.WriteLine(nodes.Current.ToString());
                    }
                    break;

                case XPathResultType.Boolean:
                    if ((bool)navigator.Evaluate(expression))
                        Console.WriteLine("True!");
                    break;

                case XPathResultType.String:
                    Console.WriteLine(navigator.Evaluate(expression));
                    break;
            }
        }

    }
}

源代码：/Files/cleo/XPathNavigator.rar