<?xml version="1.0" encoding="ISO-8859-1"?>
<bookstore>

  <book category="COOKING">
    <title lang="en">Everyday Italian</title>
    <author>Giada De Laurentiis</author>
    <year>2005</year>
    <price>30.00</price>
  </book>

  <book category="CHILDREN">
    <title lang="en">Harry Potter</title>
    <author>J K. Rowling</author>
    <year>2005</year>
    <price>29.99</price>
  </book>

  <book category="WEB">
    <title lang="en">XQuery Kick Start</title>
    <author>James McGovern</author>
    <author>Per Bothner</author>
    <author>Kurt Cagle</author>
    <author>James Linn</author>
    <author>Vaidyanathan Nagarajan</author>
    <year>2003</year>
    <price>49.99</price>
  </book>

  <book category="WEB">
    <title lang="en">Learning XML</title>
    <author>Erik T. Ray</author>
    <year>2003</year>
    <price>39.95</price>
  </book>

</bookstore>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Xml;

namespace XmlProcessTest
{
    public class Program
    {
        /// <summary>
        /// 加載XML文件
        /// </summary>
        /// <param name="xmlFilePath">XML文件路徑</param>
        /// <returns></returns>
        public static XmlDocument LoadXmlDoc(string xmlFilePath)
        {
            var xmlDoc = new XmlDocument();
            xmlDoc.Load(xmlFilePath);

            return xmlDoc;
        }

        /// <summary>
        /// 根據指定的XPath表達式獲取XML結點列表
        /// </summary>
        /// <param name="xmlDoc"></param>
        /// <param name="xpathExpr"></param>
        /// <returns></returns>
        public static XmlNodeList GetXmlNodes(XmlDocument xmlDoc, string xpathExpr)
        {
            if (xmlDoc == null)
                return null;

            return xmlDoc.SelectNodes(xpathExpr);
        }

        public static string GetXmlNodeInfo(XmlNode node, string type="xml")
        {
            if (node == null)
                return "Empty node or error node";

            string xmlNodeInfo = null;
            switch (type)
            {
                case "text":
                    xmlNodeInfo = node.InnerText;
                    break;
                default:
                    xmlNodeInfo = node.InnerXml;
                    break;
            }

            return xmlNodeInfo;
        }

        public static void Main(string[] args)
        {
            var xmlDoc = LoadXmlDoc(@"你的books.xml文件路徑");

            var rootExpr = "/bookstore";   //  根節點對應的XPath表達式
            var rootNode = GetXmlNodes(xmlDoc, rootExpr);   //
            Console.WriteLine("XPath表達式為 /bookstore，根節點bookstore的所有子節點XML內容如下：");
            Console.WriteLine(GetXmlNodeInfo(rootNode[0]));

            Console.WriteLine();

            var allBooksExpr = "/bookstore/book"; // 根節點bookstore的子元素的所有子節點
            var bookNodes = GetXmlNodes(xmlDoc, allBooksExpr);
            Console.WriteLine("XPath表達式為 bookstore/book，book節點共有：" + bookNodes.Count);

            Console.WriteLine();

            var anyBookExpr = "http://book"; // 選取所有book子元素，而不管它們在文檔中的位置
            var anyBookNodes = GetXmlNodes(xmlDoc, anyBookExpr);
            Console.WriteLine("XPath表達式為 //book，book節點共有：" + anyBookNodes.Count);
            Console.WriteLine(anyBookNodes[0].InnerXml);
            Console.WriteLine(anyBookNodes[0].OuterXml);

            Console.WriteLine();

            var categoryExpr = "http://@category";   // 選取名為category的所有屬性
            var allCategoryNodes = GetXmlNodes(xmlDoc, categoryExpr);
            Console.WriteLine("XPath表達式為 //@category，category節點共有：" + allCategoryNodes.Count);
            Console.WriteLine(allCategoryNodes[0].InnerText);
            Console.WriteLine(allCategoryNodes[0].InnerXml);

            Console.WriteLine();

            var titleWithLangExpr = "http://title[@lang]";   // 選取所有帶有lang屬性的title節點
            var titleWithLangNodes = GetXmlNodes(xmlDoc, titleWithLangExpr);
            Console.WriteLine("XPath表達式為 //title[@lang]，帶lang屬性的title節點共有：" + titleWithLangNodes.Count);
            Console.WriteLine(GetXmlNodeInfo(titleWithLangNodes[0]));

            var englishTitleExpr = "http://title[@lang='en']";   // 選取所有lang屬性值為en的title節點
            var englishTitleNodes = GetXmlNodes(xmlDoc, englishTitleExpr);
            Console.WriteLine("XPath表達式為 //title[@lang='en']，lang屬性值為en的title節點共有：" + englishTitleNodes.Count);
            Console.WriteLine(GetXmlNodeInfo(englishTitleNodes[0]));

            Console.WriteLine();

            // 使用索引的XPath查詢
            var indexExpr = "/bookstore/book[1]";   // 取bookstore子元素的第一個book元素
            var firstBookNode = GetXmlNodes(xmlDoc, indexExpr);
            Console.WriteLine("XPath表達式為 /bookstore/book[1]，節點數為：" + firstBookNode.Count);
            Console.WriteLine(GetXmlNodeInfo(firstBookNode[0]));

            Console.WriteLine();

            var indexExpr2 = "/bookstore/book[last()]"; // 取bookstore子元素的最后一個book元素
            var lastBookNode = GetXmlNodes(xmlDoc, indexExpr2);
            Console.WriteLine("XPath表達式為 /bookstore/book[last()]，節點數為：" + lastBookNode.Count);
            Console.WriteLine(GetXmlNodeInfo(lastBookNode[0]));

            Console.WriteLine();

            var indexExpr3 = "/bookstore/book[last()-1]"; // 取bookstore子元素的倒數第二個book元素
            var nextByLastBookNode = GetXmlNodes(xmlDoc, indexExpr3);
            Console.WriteLine("XPath表達式為 /bookstore/book[last()-1]，節點數為：" + lastBookNode.Count);
            Console.WriteLine(GetXmlNodeInfo(nextByLastBookNode[0]));

            Console.WriteLine();

            var indexExpr4 = "/bookstore/book[position()<3]"; // 取bookstore的前兩個book子元素
            var firstTwoBookNodes = GetXmlNodes(xmlDoc, indexExpr4);
            Console.WriteLine("XPath表達式為 /bookstore/book[position()<3]，節點數為：" + firstTwoBookNodes.Count);
            Console.WriteLine(GetXmlNodeInfo(firstTwoBookNodes[0]));

            Console.WriteLine();

            // 帶屬性值過濾條件的XPath表達式
            var fileterExpr = "/bookstore/book[price>35.00]";   // 選取bookstore的所有price屬性值大于35.00的book元素
            var bookGt35Nodes = GetXmlNodes(xmlDoc, fileterExpr);
            Console.WriteLine("XPath表達式為 /bookstore/book[price>35.00]，節點數為：" + bookGt35Nodes.Count);
            Console.WriteLine(GetXmlNodeInfo(bookGt35Nodes[0]));

            // 通配符
            // @*                匹配任何屬性節點
            // node()             匹配任何類型的節點
            // /bookstore/*   選取 bookstore 元素的所有子元素
            // //*                   選取文檔的所有元素
            // //title[@*]        選取所有帶有屬性的 title 元素
            var allTitleWithAttrExpr = "http://title[@*]";
            var allTitleWithAttrNodes = GetXmlNodes(xmlDoc, allTitleWithAttrExpr);
            Console.WriteLine("XPath表達式為 title[@*]，節點數為：" + allTitleWithAttrNodes.Count);
            Console.WriteLine(GetXmlNodeInfo(allTitleWithAttrNodes[0]));

            Console.WriteLine();

            // |        或
            var titleAndPriceExpr = "http://book/title | //book/price";
            var titleAndPriceNodes = GetXmlNodes(xmlDoc, titleAndPriceExpr);
            Console.WriteLine("XPath表達式為 //book/title | //book/price，節點數為：" + titleAndPriceNodes.Count);
            Console.WriteLine(GetXmlNodeInfo(titleAndPriceNodes[0]));

            // text()  選取文本
            var titleTextExpr = "http://title/text()";
            var titleTextNodes = GetXmlNodes(xmlDoc, titleTextExpr);
            Console.WriteLine("XPath表達式為 //title/text()，節點數為：" + titleTextNodes.Count);
            Console.WriteLine(titleTextNodes[0].Value); // 文本節點的值

            Console.ReadKey();
        }
    }
}