XmlDocument 并使用 xPath 获取特定属性
我在这里看到了几个示例，其中 Xpath 与 XmlDocument 结合使用以从 XmlDocument 节点获取特定属性......示例
Console.WriteLine(xmlDocument.SelectSingleNode("//dataTemplateSpecification/templates/template/elements/element/@name").Value.ToString());
出于某种原因，我收到“对象引用未设置为对象的实例。 ”例外。每当我遇到那行特定的代码时。我有一个小测试应用程序，在将不同的东西放入我的主项目之前，我已经设置了它来测试它们...
这是代码...
namespace ReadXml
{
class Program
{
static void Main(string[] args)
{
//string fulXmlPath = System.Web.Hosting.HostingEnvironment.MapPath("~/App_Data/templateExample.xml");
XDocument xDocument = XDocument.Load("C:\\Users\\derekww\\Documents\\XML Documents\\templateExample.xml");
XElement elem = xDocument.Element("dataTemplateSpecification"); ;
XmlDocument xmlDocument = new XmlDocument();
StreamReader file = new StreamReader("C:\\Users\\derekww\\Documents\\XML Documents\\templateExample.xml");
xmlDocument.Load(file);
//XmlDocument theDoc = new XmlDocument();
//using (var xmlReader = xDocument.CreateReader())
//{
// xmlDocument.Load(xmlReader);
//}
//Console.WriteLine(elem.ToString());
XmlNode xNode = xmlDocument.SelectSingleNode("//dataTemplateSpecification/templates/template/elements/element");
Console.WriteLine("WORK PLEASE!!!! {0}", xNode.Value.ToString());
//Console.WriteLine(xmlDocument.SelectSingleNode("//dataTemplateSpecification/templates/template/elements/element/@name").Value.ToString());
//Console.WriteLine("This better Work>>>> {0}", xmlDocument.Attributes["/dataTemplateSpecification/templates/template/elements/element/@name"].Value);
Console.ReadLine();
//Console.WriteLine("This better Work>>>> {0}", xmlDocument.SelectSingleNode("//dataTemplateSpecification/templates/template/elements/element/@name").Value);
//foreach (String AttVal in xmlDocument.SelectSingleNode("//dataTemplateSpecification/templates/template/elements/element/@name").Value)
{
//Console.WriteLine("This better Work>>>> {0}", AttVal);
}
}
}
}
这是我使用的 XML 的一部分...
<?xml version="1.0" encoding="utf-8"?>
<dataTemplateSpecification id="id1" name="name1" xmlns="http://EADIS.upmc.com /DataTemplateSpecification.xsd">
<description xmlns="">
<html>text</html>
</description>
<templates xmlns="">
<template>
<elements>
<element id="element0" name="PatientId" display="Patient ID" dataType="String" value="0101010111111" visable="false" readOnly="true">
<validation>
<rules>
<rule id="0" test="#element0.value == ''">
<fail>
<html><b>Patient ID is null, value must be present</b></html>
</fail>
</rule>
</rules>
</validation>
</element>
</elements>
</template>
<templates>
我只是向您展示了需要了解 xml 结构的部分。我向你保证它的结构良好。我想我之前问过这个问题，但不知何故它没有被发布（也许我忘了，谁知道）。任何对此的帮助将不胜感激。如果我找到它不起作用的原因，我一定会让你们知道。
谢谢。
I have seen a couple of examples on here where Xpath is used in conjunction with XmlDocument to get a specific attribute from an XmlDocument Node.... Example
Console.WriteLine(xmlDocument.SelectSingleNode("//dataTemplateSpecification/templates/template/elements/element/@name").Value.ToString());
For some reason I am getting a "Object reference not set to an instance of an object." exception. Whenever I run across that particular line of code. I have a little test app that I have set up to test out different things before I put them into my main project...
Here is the code for that...
namespace ReadXml
{
class Program
{
static void Main(string[] args)
{
//string fulXmlPath = System.Web.Hosting.HostingEnvironment.MapPath("~/App_Data/templateExample.xml");
XDocument xDocument = XDocument.Load("C:\\Users\\derekww\\Documents\\XML Documents\\templateExample.xml");
XElement elem = xDocument.Element("dataTemplateSpecification"); ;
XmlDocument xmlDocument = new XmlDocument();
StreamReader file = new StreamReader("C:\\Users\\derekww\\Documents\\XML Documents\\templateExample.xml");
xmlDocument.Load(file);
//XmlDocument theDoc = new XmlDocument();
//using (var xmlReader = xDocument.CreateReader())
//{
// xmlDocument.Load(xmlReader);
//}
//Console.WriteLine(elem.ToString());
XmlNode xNode = xmlDocument.SelectSingleNode("//dataTemplateSpecification/templates/template/elements/element");
Console.WriteLine("WORK PLEASE!!!! {0}", xNode.Value.ToString());
//Console.WriteLine(xmlDocument.SelectSingleNode("//dataTemplateSpecification/templates/template/elements/element/@name").Value.ToString());
//Console.WriteLine("This better Work>>>> {0}", xmlDocument.Attributes["/dataTemplateSpecification/templates/template/elements/element/@name"].Value);
Console.ReadLine();
//Console.WriteLine("This better Work>>>> {0}", xmlDocument.SelectSingleNode("//dataTemplateSpecification/templates/template/elements/element/@name").Value);
//foreach (String AttVal in xmlDocument.SelectSingleNode("//dataTemplateSpecification/templates/template/elements/element/@name").Value)
{
//Console.WriteLine("This better Work>>>> {0}", AttVal);
}
}
}
}
Here is part of the XML that I used...
<?xml version="1.0" encoding="utf-8"?>
<dataTemplateSpecification id="id1" name="name1" xmlns="http://EADIS.upmc.com /DataTemplateSpecification.xsd">
<description xmlns="">
<html>text</html>
</description>
<templates xmlns="">
<template>
<elements>
<element id="element0" name="PatientId" display="Patient ID" dataType="String" value="0101010111111" visable="false" readOnly="true">
<validation>
<rules>
<rule id="0" test="#element0.value == ''">
<fail>
<html><b>Patient ID is null, value must be present</b></html>
</fail>
</rule>
</rules>
</validation>
</element>
</elements>
</template>
<templates>
I just showed you the part that you need to understand the xml structure. I assure you that it is well formed. I think I asked this question before but somehow or the other it didn't get posted (maybe I forgot, who knows). Any help with this would be greatly appreciated. If I come up with a reason for why it isn't working I will be sure to let you guys know.
Thank You.
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评论（2）
为什么不能使用这个
XPath：Why can't you use this
XPath:您需要在代码中指定 XML 文件的命名空间。
请参阅此处了解更多信息：当根节点有属性时如何选择xml根节点？
You need to specify the namespace of the XML file in your code.
See here for more info: How to select xml root node when root node has attribute?