没有使用XPath从Atom XML文档中选择节点？ [英] No Nodes Selected from Atom XML document using XPath?

问题描述

我正在尝试以编程方式解析Atom供稿。我将原子XML下载为字符串。我可以将XML加载到 XmlDocument 中。但是，我无法使用XPath遍历文档。每当我尝试时，都会得到 null 。

I'm trying to parse an Atom feed programmatically. I have the atom XML downloaded as a string. I can load the XML into an XmlDocument. However, I can't traverse the document using XPath. Whenever I try, I get null.

我一直在使用此Atom提要作为测试： http://steve-yegge.blogspot.com/feeds/posts/default

I've been using this Atom feed as a test: http://steve-yegge.blogspot.com/feeds/posts/default

调用 SelectSingleNode（）始终返回 null ，当我使用 / 时。这是我现在正在尝试的方法：

Calling SelectSingleNode() always returns null, except for when I use "/". Here is what I'm trying right now:

using (WebClient wc = new WebClient())
{
    string xml = wc.DownloadString("http://steve-yegge.blogspot.com/feeds/posts/default");
    XmlNamespaceManager nsMngr = new XmlNamespaceManager(new NameTable());
    nsMngr.AddNamespace(string.Empty, "http://www.w3.org/2005/Atom");
    nsMngr.AddNamespace("app", "http://purl.org/atom/app#");
    XmlDocument atom = new XmlDocument();
    atom.LoadXml(xml);
    XmlNode node = atom.SelectSingleNode("//entry/link/app:edited", nsMngr);
}

我认为可能是因为我的XPath，所以我也因为我知道根节点应该工作，所以尝试了一个简单的根节点查询：

I thought it might have been because of my XPath, so I've also tried a simple query of the root node since I knew the root should work:

// I've tried both with & without the nsMngr declared above
XmlNode node = atom.SelectSingleNode("/feed");

无论我做什么，似乎都无法选择。显然我遗漏了一些东西，只是无法弄清楚是什么。为了使XPath可以在此Atom订阅源上工作，我需要做什么？

No matter what I do, it seems like it can't select anything. Obviously I'm missing something, I just can't figure out what. What is it that I need to do in order to make XPath work on this Atom feed?

尽管这个问题有答案，但我发现这个问题几乎是重复的： SelectNodes无法使用stackoverflow feed

推荐答案

C＃实现可能允许使用默认名称空间（我不知道），而XPath 1.0规范则不允许。因此，给 Atom加上自己的前缀：

While the C# implementation may allow default namespaces (I don't know), the XPath 1.0 spec doesn't. So, give "Atom" its own prefix:

nsMngr.AddNamespace("atom", "http://www.w3.org/2005/Atom");

然后适当地更改XPath：

And change your XPath appropriately:

XmlNode node = atom.SelectSingleNode("//atom:entry/atom:link/app:edited", nsMngr);

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