XML：未将对象引用设置为对象的实例

发布于 2024-10-29 18:12:03 字数 1324 浏览 2 评论 0原文

<?xml version="1.0" encoding="utf-8" ?>
<siteMap xmlns="http://schemas.microsoft.com/AspNet/SiteMap-File-1.0" >
    <siteMapNode url="~/" title="Úvodní stránka">
        <siteMapNode url="Pocitace" title="Počítače" />
        <siteMapNode url="Elektronika" title="Elektronika" />
    </siteMapNode>
</siteMap>

我向该文件写入新数据：

XmlDocument originalXml = new XmlDocument();
originalXml.Load(Server.MapPath("../../Web.sitemap"));
XmlAttribute title = originalXml.CreateAttribute("title");
title.Value = newCategory;
XmlAttribute url = originalXml.CreateAttribute("url");
url.Value = seoCategory;
XmlNode newSub = originalXml.CreateNode(XmlNodeType.Element, "siteMapNode", null);
newSub.Attributes.Append(title);
newSub.Attributes.Append(url);
originalXml.SelectSingleNode("siteMapNode").AppendChild(newSub);

但我得到：

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.
Source Error: 
Line 49: newSub.Attributes.Append(title);
Line 50: newSub.Attributes.Append(url);
Line 51: originalXml.SelectSingleNode("siteMapNode").AppendChild(newSub);

第 51 行 si 红色。你能帮我吗？

（Web.sitemap 我在根文件中，代码在 Someting/Someting/Someting.aspx 中，所以我认为地址是正确的。）

原文

<?xml version="1.0" encoding="utf-8" ?>
<siteMap xmlns="http://schemas.microsoft.com/AspNet/SiteMap-File-1.0" >
    <siteMapNode url="~/" title="Úvodní stránka">
        <siteMapNode url="Pocitace" title="Počítače" />
        <siteMapNode url="Elektronika" title="Elektronika" />
    </siteMapNode>
</siteMap>

And I write to this file new data:

XmlDocument originalXml = new XmlDocument();
originalXml.Load(Server.MapPath("../../Web.sitemap"));
XmlAttribute title = originalXml.CreateAttribute("title");
title.Value = newCategory;
XmlAttribute url = originalXml.CreateAttribute("url");
url.Value = seoCategory;
XmlNode newSub = originalXml.CreateNode(XmlNodeType.Element, "siteMapNode", null);
newSub.Attributes.Append(title);
newSub.Attributes.Append(url);
originalXml.SelectSingleNode("siteMapNode").AppendChild(newSub);

But I get:

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.
Source Error: 
Line 49: newSub.Attributes.Append(title);
Line 50: newSub.Attributes.Append(url);
Line 51: originalXml.SelectSingleNode("siteMapNode").AppendChild(newSub);

Line 51 si red. Can u help me?

(Web.sitemap i have in root file and code I have in Someting/Someting/Someting.aspx, so adrress is correct i think.)

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蓝梦月影 2024-11-05 18:12:03

对 originalXml.SelectSingleNode("siteMapNode") 的调用返回 null。您需要指定名称空间。

更新：
使用此代码而不是引发异常的行（第 51 行）：

XmlNamespaceManager nsmanager = new XmlNamespaceManager(originalXml.NameTable);
nsmanager.AddNamespace("x", "http://schemas.microsoft.com/AspNet/SiteMap-File-1.0");
originalXml.SelectSingleNode("x:siteMap/x:siteMapNode", nsmanager).AppendChild(newSub);

说明：
您犯了两个错误：

用于查找 siteMapNode 的 XPath 查询不正确。按照您编写的方式，它仅查看名为“siteMapNode”的标签的根标签
。根标签“siteMap”指定一个名称空间。您需要在调用 SelectSingleNode 时使用该命名空间

The call to originalXml.SelectSingleNode("siteMapNode") returns null. You need to specify the namespace.

Update:
Use this code instead of the line that throws the exception (Line 51):

XmlNamespaceManager nsmanager = new XmlNamespaceManager(originalXml.NameTable);
nsmanager.AddNamespace("x", "http://schemas.microsoft.com/AspNet/SiteMap-File-1.0");
originalXml.SelectSingleNode("x:siteMap/x:siteMapNode", nsmanager).AppendChild(newSub);

Explanation:
You made two mistakes:

Your XPath query to find the siteMapNode was not correct. The way you wrote it, it looked only at the root tag for the tag with the name "siteMapNode"
The root tag "siteMap" specifies a namespace. You need to use that namespace in your call to SelectSingleNode

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