如何使用 C# xmlreader 类获取 XML 中特定元素的值答案

【问题标题】：How to grab the value of particular element in XML using C# xmlreader class如何使用 C# xmlreader 类获取 XML 中特定元素的值
【发布时间】：2017-05-19 11:14:53
【问题描述】：

我有这个 XML 文件，我想在其中使用 C# xmlreader 类读取书籍 ID“bk101”的作者和标题的值。我无法获取该特定 ID 的作者和标题的值。

<?xml version="1.0"?>
<catalog>
   <book id="bk101">
      <author>Gambardella, Matthew</author>
      <title>XML Developer's Guide</title>
      <genre>Computer</genre>
      <price>44.95</price>
      <publish_date>2000-10-01</publish_date>
      <description>An in-depth look at creating applications 
      with XML.</description>
   </book>
   <book id="bk102">
      <author>Ralls, Kim</author>
      <title>Midnight Rain</title>
      <genre>Fantasy</genre>
      <price>5.95</price>
      <publish_date>2000-12-16</publish_date>
      <description>A former architect battles corporate zombies, 
      an evil sorceress, and her own childhood to become queen 
      of the world.</description>
   </book>
   <book id="bk103">
      <author>Corets, Eva</author>
      <title>Maeve Ascendant</title>
      <genre>Fantasy</genre>
      <price>5.95</price>
      <publish_date>2000-11-17</publish_date>
      <description>After the collapse of a nanotechnology 
      society in England, the young survivors lay the 
      foundation for a new society.</description>
   </book>
   <book id="bk104">
      <author>Corets, Eva</author>
      <title>Oberon's Legacy</title>
      <genre>Fantasy</genre>
      <price>5.95</price>
      <publish_date>2001-03-10</publish_date>
      <description>In post-apocalypse England, the mysterious 
      agent known only as Oberon helps to create a new life 
      for the inhabitants of London. Sequel to Maeve 
      Ascendant.</description>
   </book>
   <book id="bk105">
      <author>Corets, Eva</author>
      <title>The Sundered Grail</title>
      <genre>Fantasy</genre>
      <price>5.95</price>
      <publish_date>2001-09-10</publish_date>
      <description>The two daughters of Maeve, half-sisters, 
      battle one another for control of England. Sequel to 
      Oberon's Legacy.</description>
   </book>
   <book id="bk106">
      <author>Randall, Cynthia</author>
      <title>Lover Birds</title>
      <genre>Romance</genre>
      <price>4.95</price>
      <publish_date>2000-09-02</publish_date>
      <description>When Carla meets Paul at an ornithology 
      conference, tempers fly as feathers get ruffled.</description>
   </book>
   <book id="bk107">
      <author>Thurman, Paula</author>
      <title>Splish Splash</title>
      <genre>Romance</genre>
      <price>4.95</price>
      <publish_date>2000-11-02</publish_date>
      <description>A deep sea diver finds true love twenty 
      thousand leagues beneath the sea.</description>
   </book>
   <book id="bk108">
      <author>Knorr, Stefan</author>
      <title>Creepy Crawlies</title>
      <genre>Horror</genre>
      <price>4.95</price>
      <publish_date>2000-12-06</publish_date>
      <description>An anthology of horror stories about roaches,
      centipedes, scorpions  and other insects.</description>
   </book>
   <book id="bk109">
      <author>Kress, Peter</author>
      <title>Paradox Lost</title>
      <genre>Science Fiction</genre>
      <price>6.95</price>
      <publish_date>2000-11-02</publish_date>
      <description>After an inadvertant trip through a Heisenberg
      Uncertainty Device, James Salway discovers the problems 
      of being quantum.</description>
   </book>
   <book id="bk110">
      <author>O'Brien, Tim</author>
      <title>Microsoft .NET: The Programming Bible</title>
      <genre>Computer</genre>
      <price>36.95</price>
      <publish_date>2000-12-09</publish_date>
      <description>Microsoft's .NET initiative is explored in 
      detail in this deep programmer's reference.</description>
   </book>
   <book id="bk111">
      <author>O'Brien, Tim</author>
      <title>MSXML3: A Comprehensive Guide</title>
      <genre>Computer</genre>
      <price>36.95</price>
      <publish_date>2000-12-01</publish_date>
      <description>The Microsoft MSXML3 parser is covered in 
      detail, with attention to XML DOM interfaces, XSLT processing, 
      SAX and more.</description>
   </book>
   <book id="bk112">
      <author>Galos, Mike</author>
      <title>Visual Studio 7: A Comprehensive Guide</title>
      <genre>Computer</genre>
      <price>49.95</price>
      <publish_date>2001-04-16</publish_date>
      <description>Microsoft Visual Studio 7 is explored in depth,
      looking at how Visual Basic, Visual C++, C#, and ASP+ are 
      integrated into a comprehensive development 
      environment.</description>
   </book>
</catalog>

【问题讨论】：

我知道您说过“使用 XmlReader 类”。你真的必须使用这个类，或者你只是不知道其他人（例如XElement）。
作为@ThomasD。问，为什么要使用XmlReader？根据文档，XmlReader '表示提供对 XML 数据的快速、非缓存、只进访问的阅读器'。如果你真的想从根向内访问每个节点，你应该只使用这样的东西。对于您在问题中提出的问题，带有 XDocument 之类的 XPath 更有意义。
实际上我已经开始使用 XmlReader 类解决这个问题，因为我不知道任何其他方法。如果其他方法很简单，请告诉我。

标签： c# xml visual-studio ssis xmlreader

【解决方案1】：

我认为您可以将 LINQ 用于 xml 技术。但是，如果您想使用 XMLReader 类，您可以使用以下代码 sn-p

using (var inFile = new FileStream(path, FileMode.Open))
    {
        using (var reader = new XmlTextReader(inFile))
        {
            while (reader.Read())
            {

                        if ( reader.NodeType == XmlNodeType.Element && reader.Name == "book" && reader.GetAttribute(0) == "bk103")
                        {


                        }

                }
            }
        }
    }

【讨论】：

之后如何读取该书ID的作者和书名的值？

【解决方案2】：

这是一个简单的实现（当然可以改进）：

        bool isFoundId = false;
        string title = string.Empty;
        string author = string.Empty;

        using (var str = File.OpenRead("data.xml"))
        {
            using (XmlReader reader = new XmlTextReader(str))
            {
                while (reader.Read())
                {
                    if (reader.Name == "book")
                    {
                        var v = reader.GetAttribute("id");
                        if (v == "bk101")
                        {
                            isFoundId = true;
                        }
                        else if (isFoundId)
                        {
                            break;
                        }
                    }
                    if (isFoundId && reader.Name == "title")
                    {
                        title = reader.ReadElementContentAsString();
                    }
                    if (isFoundId && reader.Name == "author")
                    {
                        author = reader.ReadElementContentAsString();
                    }
                }
            }
        }

【讨论】：

【解决方案3】：

这就是您使用 XPath 执行此操作的方式。我假设您的 xml 在文件中，但您可以将任何有效的 XML 字符串传递给 XDocument.Parse 方法。

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

namespace StackOverflow
{
    class Program
    {
        static void Main(string[] args)
        {
            string catalog = System.IO.File.ReadAllText("catalog.xml");

            System.Xml.Linq.XDocument xdoc = System.Xml.Linq.XDocument.Parse(catalog);

            var targetBook = xdoc.XPathSelectElement("//catalog/book[@id='bk101']");
            var targetBookTitle = targetBook.XPathSelectElement("title").Value;
            var targetBookAuthor = targetBook.XPathSelectElement("author").Value;

            Console.Write($"{ targetBookTitle} - { targetBookAuthor}");
            Console.Read();

        }
    }
}

【讨论】：

【解决方案4】：

对于大型 xml 文件，xmlreader 是最好的方法。这是我认为最好的解决方案。它结合使用 xmlreader 和 xml linq。

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

namespace ConsoleApplication3
{
    class Program
    {
        const string FILENAME = @"c:\temp\test.xml";
        public static void Main(string[] args)
        {
            new Book(FILENAME);
        }
    }
    public class Book
    {
        public static List<Book> books = new List<Book>();

        string id { get; set; }
        string title { get; set; }
        string author { get; set; }

        public Book() { }
        public Book(string filename)
        {
            XmlReader reader = XmlReader.Create(filename);

            while (!reader.EOF)
            {
                if (reader.Name != "book")
                {
                    reader.ReadToFollowing("book");
                }
                if (!reader.EOF)
                {
                    Book newBook = new Book();
                    books.Add(newBook);

                    XElement xmlBook = (XElement)XElement.ReadFrom(reader);
                    newBook.id = (string)xmlBook.Attribute("id");
                    newBook.author = (string)xmlBook.Element("author");
                    newBook.title = (string)xmlBook.Element("title");
                }
            }
        }
    }
}

【讨论】：

【解决方案5】：

正如所暗示的，解决此问题的最简单方法是使用 LINQ to XML，除非您有一个非常大的 XML 文档。简洁明了：

var query =
    from book in doc.Descendants("book")
    where (string) book.Attribute("id") == "bk101"
    select new
    {
        Author = (string) book.Element("author"),
        Title = (string) book.Element("title")
    };

var result = query.Single();

请参阅this fiddle 以获取演示。

【讨论】：