这个XPath查询有什么问题?

I'm trying to select nodes from an rss feed. It works fine for Twitter, but I can't do it on Youtube.

我正在尝试从rss提要中选择节点。它在Twitter上运行得很好，但在Youtube上我做不到。

        string youtube = "http://gdata.youtube.com/feeds/api/users/CTVOlympics/uploads";
        string twitter = "http://twitter.com/statuses/user_timeline/ctvolympics.rss";

        //this populates the XmlNodeList object
        XmlTextReader readerTwitter = new XmlTextReader(twitter);
        XmlDocument docTwitter = new XmlDocument();
        docTwitter.Load(readerTwitter);
        XmlNodeList nodesTwitter = docTwitter.SelectNodes("/rss/channel/item");

        //this doesn't populate the object
        XmlTextReader readerYoutube = new XmlTextReader(youtube);
        XmlDocument docYoutube = new XmlDocument();
        docYoutube.Load(readerYoutube);
        XmlNodeList nodesYoutube = docYoutube.SelectNodes("/feed/entry");

any ideas?

什么好主意吗?

7 个解决方案

#1

You're attempting to select the node 'entry' in an empty namespace, whereas you should be trying to select the node 'entry' in the namespace 'http://www.w3.org/2005/Atom'.

您正在尝试在一个空的名称空间中选择节点“entry”，而您应该尝试在名称空间“http://www.w3.org/2005/Atom”中选择节点“entry”。

You can use XMLNamespaceManager to specify a default namespace:

可以使用XMLNamespaceManager指定一个默认名称空间:

XmlNamespaceManager nsmanager = new XmlNamespaceManager(docYoutube.NameTable);
nsmanager.AddNamespace(String.Empty, "http://www.w3.org/2005/Atom");

or you could use "/*[local-name()='feed']/*[local-name()='entry']"

或者你可以使用“/ *[本地名称()= '喂']/ *[本地名称()=“条目”)”

#2

Specify the namespace.

指定名称空间。

#3

If you want to visualize the result of XPath queries, you can use the XpathVisualizer. It's a WinForms tool. Load the XML document you want to query, key in the query, view the results.

如果希望可视化XPath查询的结果，可以使用XpathVisualizer。这是一个WinForms的工具。加载要查询的XML文档，在查询中键入，查看结果。

alt text http://i45.tinypic.com/2jb409.jpg

alt文本http://i45.tinypic.com/2jb409.jpg

Free. Open source.

免费的。开源的。

#4

If it does not generate an error, it must be because the xml-document doesn't contain a <feed>-element, or <entry> elements with a <feed>-parent.

如果它没有生成错误，那一定是因为xml文档不包含 -element，或者 element with -parent。

#5

Try getting at the base of the problem by using the // instead of /. So something like //entry my work better as it will plumb the depths looking for your request.

试着用/而不是/来解决问题的根本。因此，我的工作做得更好，因为它会使你的要求更加深入。

But my question is whether that XPath query is actually retrieving anything.

但我的问题是，这个XPath查询是否正在检索任何内容。

#6

string youtube = "http://gdata.youtube.com/feeds/api/users/CTVOlympics/uploads";
string twitter = "http://twitter.com/statuses/user_timeline/ctvolympics.rss";

//this populates the XmlNodeList object
XmlDocument docTwitter;
using (var readerTwitter = XmlReader.Create(twitter))
{
    docTwitter = new XmlDocument();
    docTwitter.Load(readerTwitter);
}
XmlNodeList nodesTwitter = docTwitter.SelectNodes("/rss/channel/item");

//this doesn't populate the object
XmlDocument docYoutube;
using (var readerYoutube = XmlReader.Create(youtube))
{
    docYoutube = new XmlDocument();
    docYoutube.Load(readerYoutube);
}
XmlNamespaceManager ns = new XmlNamespaceManager(docYoutube.NameTable);
ns.AddNamespace("atom", "http://www.w3.org/2005/Atom");
XmlNodeList nodesYoutube = docYoutube.SelectNodes("/atom:feed/atom:entry", ns);

#7

Give this a try: "/*[local-name()='feed']/*[local-name()='entry']"

给这一个尝试:“/ *(本地名称()= '喂']/ *[本地名称()=“条目”)”

#1