如何在SyndicationFeed中使用非标准名称空间？

Question

Good day. First, let me warn you: My knowledge of XML is basic, so I may have found the correct answer in my research and just not understood how to apply it.

I currently have some C# code that reads a National Weather Service XML file and looks for text in an element to decide whether or not there is a weather alert. That works, but I'd much rather test for the existence of another element and then use its text to write the alert out to a web page. An example of an XML file with a warning is here: http://www.co.frederick.va.us/dev/scrapewarning.xml . I want to test for the existence of <cap:event> and then use its text to fill a literal on a web page.

Here's what I'm doing now:

// Create an instance of XmlReader with the warning feed and then load it into a SyndicationFeed.
XmlReader reader = XmlReader.Create(strWarningFeed);
SyndicationFeed feed = SyndicationFeed.Load(reader);

// Read through the XML, pull out the items we need depending on whether or not there is a warning.
foreach (var str in feed.Items)
{
    if (str.Title.Text.Contains("no active"))
    {
        weatherWarning.Visible = false;
    }
    else
    {
        string strTitle = str.Title.Text;
        string strId = str.Id.ToString();
        strTitle = strTitle.Substring(0, strTitle.LastIndexOf("issued"));
        litOut.Text += String.Format("<p class=\"warningText\">{0}</p><p class=\"warningText\"><a href=\"{1}\">Read more.</a></p>", strTitle, strId);
    }
}

So, instead of seeing it the title contains "no active", I'd rather ask if the document has an element called <cap:event> and then use its text. Pseduocode:

foreach (var str in feed.Items)
{
    if (<cap:event> doesn't exist)
    {
        weatherWarning.Visible = false;
    }
    else
    {
        string strTitle = <cap:event>.Text;
    }
}

Let me know if you need more info. Thanks in advance for help.

Answer 1

Something like checking for the existence of (and therefore any existing values) is a lot easier with linq to xml. If you load the xml into an XDocument you can then use the goodness of linq to query elements and descendants. Without being in front of an IDE or able to have a very close look at that sample xml, something like doc.Descendants("weather").Where(e => e.Element("event") == "whatever").

Answer 2

I believe you are missing a namespace manager. Here is how the code would work with XmlDocument:

        var xmlDoc = new XmlDocument();
        xmlDoc.Load(@"http://www.co.frederick.va.us/dev/scrapewarning.xml");
        var nsm = new XmlNamespaceManager(xmlDoc.NameTable);
        nsm.AddNamespace("s", "http://www.w3.org/2005/Atom");
        nsm.AddNamespace("cap", "urn:oasis:names:tc:emergency:cap:1.1");
        var nodes = xmlDoc.SelectNodes("//s:entry[cap:event]", nsm);