使用 XPath 和 VB.NET 解析包含命名空间的 XML

Using XPath and VB.NET to parse XML containing namespsaces

提问by DWRoelands

There are several related questions, but none which provide the guidance I need.

有几个相关的问题，但没有一个可以提供我需要的指导。

Assuming the following XML:

假设以下 XML：

<?xml-stylesheet href="http://www.blogger.com/styles/atom.css" type="text/css"?>
<feed xmlns="http://www.w3.org/2005/Atom"  xmlns:openSearch="http://a9.com/-/spec/opensearchrss/1.0/"  xmlns:blogger="http://schemas.google.com/blogger/2008"  xmlns:georss="http://www.georss.org/georss"  xmlns:gd="http://schemas.google.com/g/2005"  xmlns:thr="http://purl.org/syndication/thread/1.0" >
<entry>
<title type="text">This is the title</title>
<content>lorem ipsum</content>
</entry>
<entry>
<title type="text">This is the second title</title>
<content>lorem ipsum 2</content>
</entry>
</feed>

If this document had no namespaces, I could write code like this:

如果这个文档没有命名空间，我可以写这样的代码：

Public Sub ShowXML(XmlText As String)
    Dim doc As New XmlDocument
    doc.LoadXml(XmlText)
    For Each Entry As XmlNode In doc.SelectNodes("//entry")
        Console.WriteLine(Entry.SelectSingleNode("title").InnerText)
    Next
End Sub

Because of namespaces, this is not possible. This is my latest attempt:

由于命名空间，这是不可能的。这是我最近的尝试：

Public Sub ShowXML(XmlText As String)
    Dim doc As New XmlDocument
    doc.LoadXml(XmlText)
    Dim nsmgr As New XmlNamespaceManager(doc.NameTable)
    nsmgr.AddNamespace("rss", "http://www.w3.org/2005/Atom")
    For Each Entry As XmlNode In doc.SelectNodes("//rss:entry")
        Console.WriteLine(Entry.SelectSingleNode("/rss:title").InnerText)
    Next
End Sub

What is the correct XPath syntax to get the "title"?

获取“标题”的正确 XPath 语法是什么？

Reasons why this is a separate question from other ones on similar topics:

这是一个与类似主题的其他问题不同的问题的原因：

1. Most of the other examples are C#, and I am looking for a VB.NET solution.
2. The other examples do not address the scenario of navigating to a node from a previously-selected node.

1. 大多数其他示例都是 C#，我正在寻找 VB.NET 解决方案。
2. 其他示例没有解决从先前选择的节点导航到节点的情况。

I am not looking for a solution that strips namespaces; I want to understand them. Thank you.

我不是在寻找去除命名空间的解决方案；我想了解他们。谢谢你。

回答by Dave Michener

Your inner XPath, /rss:title, has a leading /which indicates that this search should begin from the top of the document regardless of the fact that you are currently on a child node.

您的内部 XPath/rss:title有一个前导/，它表明无论您当前是否在子节点上，此搜索都应从文档顶部开始。

Instead just use rss:titleand you'll get the node you are after.

而只是使用rss:title，你会得到你所追求的节点。