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c# - 如何从 XmlNode 对象寻址子节点？

问题描述

这是我的测试 XML 文档：

<?xml version="1.0" encoding="utf-8" ?>
<foos>
  <foo>
    <bar>
      <bazs>
        <baz>baz1</baz>
        <baz>baz2</baz>
        <baz>baz3</baz>
      </bazs>
    </bar>
  </foo>
  <!--there will be other foo nodes with same structure but different number of baz nodes-->
</foos>

在本文档中，每个<foo>节点都有一个<bar>节点，每个<bar>节点都有一个节点列表<baz>。我想<baz>从每个<bar>. 这是我的代码：

using System;
using System.Xml;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            XmlDocument xmlDocument = new XmlDocument();
            xmlDocument.Load("test.xml");
            XmlNodeList fooNodes = xmlDocument.SelectNodes("/foos/foo");
            foreach(XmlNode fooNode in fooNodes)
            {
                XmlNode barNode = fooNode.SelectSingleNode("bar");

                var bazNodes1 = fooNode.SelectNodes("/bar/bazs/baz");

                var bazNodes2 = fooNode.SelectNodes("bar/bazs/baz");

                var bazNodes3 = barNode.SelectNodes("/bazs/baz");

                Console.WriteLine($"Method 1 returned {bazNodes1.Count} nodes.");
                Console.WriteLine($"Method 2 returned {bazNodes2.Count} nodes.");
                Console.WriteLine($"Method 3 returned {bazNodes3.Count} nodes.");
            }
            Console.Read();
        }
    }
}

，产生：

Method 1 returned 0 nodes.
Method 2 returned 3 nodes.
Method 3 returned 0 nodes.

在这里，我对/while 寻址节点的用法有点困惑。虽然fooNodes从文档的根目录获取正在使用/foos/fooas xpath，但我无法从节点bazNodes使用，这对我来说很奇怪。而且我还坚持从节点获取，我认为这是因为我不知道正确的语法。所以我的问题是：/bar/bazs/baz<foo>bazNodes<bar>

  1. /在寻址节点时，我什么时候应该包括前导？
  2. 在此示例中，如何<baz>从节点获取节点？<bar>

标签： c#xmlxml-parsing

解决方案

第一个问题的答案是，如果要启动从根节点选择的绝对路径，则需要包含前导“/”。第二个问题的答案请参考下面的示例代码。另外，我推荐这篇文章供参考。

using System;
using System.Xml;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            var xmlDoc = new XmlDocument();
            xmlDoc.Load("test.xml");

            XmlNodeList fooNodes1 = xmlDoc.SelectNodes("/foos/foo/bar/bazs/*"); // starts an absolute path that selects from the root
                                                                            // foos element.
            Console.WriteLine($"Method 1 returned {fooNodes1.Count} nodes."); 

            XmlNodeList fooNodes2 = xmlDoc.SelectNodes("/foos/foo");    // "/foo" the document element(<foo>) of this document.

            foreach (XmlNode fooNode in fooNodes2)
            { 
                var bazNodes2 = fooNode.SelectNodes("./bar/bazs/baz");  // "." indicates the current node.
                var bazNodes3 = fooNode.SelectNodes("bar/bazs/baz"); // selects all baz elements that are children of an bazs element, 
                                                                 // which is itself a child of the root bar element.
                var bazNodes4 = fooNode.SelectNodes("bar/bazs/*");   // "*" selects any element in the path.
                var bazNodes5 = fooNode.SelectNodes("bar/*/baz");   
                var bazNodes6 = fooNode.SelectNodes("//bazs/*");     // selects any elements that are children of an bazs element, 
                                                                 // regardless of where bazs appear in the current context.
                var bazNodes7 = fooNode.SelectNodes("bar//baz");     // selects all the baz elements that are under an bar element, 
                                                                 // regardless of where they appear in the current context.
                var bazNodes8 = fooNode.SelectNodes("//bazs/baz");   // selects all the bazs elements that are children of an baz element, 
                                                                 // regardless of where they appear in the document.
                var bazNodes9 = fooNode.SelectNodes("//baz");        // starts a relative path that selects baz element anywhere.

                XmlNode barNode = fooNode.SelectSingleNode("bar");

                var bazNodes10 = barNode.SelectNodes("bazs/*");     // selects all nodes which are contained by a root bazs element.

                Console.WriteLine($"Method 2 returned {bazNodes2.Count} nodes.");
                Console.WriteLine($"Method 3 returned {bazNodes3.Count} nodes.");
                Console.WriteLine($"Method 4 returned {bazNodes4.Count} nodes.");
                Console.WriteLine($"Method 5 returned {bazNodes5.Count} nodes.");
                Console.WriteLine($"Method 6 returned {bazNodes6.Count} nodes.");
                Console.WriteLine($"Method 7 returned {bazNodes7.Count} nodes.");
                Console.WriteLine($"Method 8 returned {bazNodes8.Count} nodes.");
                Console.WriteLine($"Method 9 returned {bazNodes9.Count} nodes.");
                Console.WriteLine($"Method 10 returned {bazNodes10.Count} nodes.");
            }

            Console.Read();
        }
    }
}

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