How Do I Read Child Nodes Using Xelement?

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I have this piece of code that I am trying to implement.The objective is to get value from one of the nodes.

C#

string str1 = obj.GetStatusSettingsFromCamera("http://10.40.160.73/cgi/status.php?item=mfm&format=xml", "", "");
            XElement xml = XElement.Parse(str1);
            XElement findTag = xml.Elements("Firmware_CRC").FirstOrDefault();

            if (findTag != null) \\ showing null 
            {
                string firmwareTitle =Convert.ToString(findTag.Attribute("title"));
                string currentFirmware = findTag.Value;
            }

XML from URL;

HTML

<Status>
<Summary>
<Uptime>09:56:12</Uptime>
<FastWD>00:01:58</FastWD>
<SlowWD>14:03:48</SlowWD>
<Configuration_Download>Success</Configuration_Download>
<Firmware_CRC title="Compatible versions: a29d.fe3e" class="critical hastooltip">a29d.3db8</Firmware_CRC>
<Core_Version>19.6</Core_Version>
<App_Version>23.4</App_Version>
<CPLD_Version>4BF44D51</CPLD_Version>
</Summary>
<Detectors>
<state>Operating</state>
<detector>8 channel - Lane agile radar: Operating</detector>
<detector>1 channel - Wired light phase detector: Operating</detector>
<detector>Optical Light Phase Detector: Absent</detector>
<self_test>pass[00]</self_test>
<radar_error_counter>0</radar_error_counter>
</Detectors>
</Status>

If I try to find Firmware_CRC the findtag is showing null. It's a child node under Summary.
I know I am going wrong somewhere but can't figure it out.
P.S. : I am new to .NET entirely

Posted 14-Aug-14 7:53am

Anshumaan Chaturvedi

Updated 14-Aug-14 8:15am

PIEBALDconsult

v2

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2 solutions

Solution 1

~~XElement findTag = xml.Elements("//Firmware_CRC").FirstOrDefault();~~ (Thanks, Richard)

I'd use a method that supports XPath -- for more flexibility when needed:

XElement findTag = xml.XPathSelectElements("//Firmware_CRC").FirstOrDefault();

"
// Selects nodes in the document from the current node that match the selection no matter where they are
"

http://www.w3schools.com/xpath/xpath_intro.asp[^]

Posted 14-Aug-14 8:17am

PIEBALDconsult

Updated 14-Aug-14 9:07am

v5

Comments

Anshumaan Chaturvedi 14-Aug-14 14:40pm

IT's throwing :XMLException
Message:
Name cannot begin with the '/' character, hexadecimal value 0x5C.

PIEBALDconsult 14-Aug-14 14:53pm

Alas, it doesn't support XPath; more reason not to use XElement.
I'm sure this came up here recently.

Richard Deeming 14-Aug-14 14:48pm

The Elements method doesn't accept XPath queries. You would need to use the XPathSelectElements method[^] instead.

PIEBALDconsult 14-Aug-14 15:02pm

That is such a basic function of XML, why would it not be built-in? The mind boggles. I always use XmlDocument.

Richard Deeming 14-Aug-14 15:06pm

It is built-in. It's just not what the Elements method was intended to do.

If I pass a string containing an IP address to DateTime.Parse, it doesn't ping that IP address. That doesn't mean the DateTime.Parse is broken. :)

PIEBALDconsult 14-Aug-14 15:18pm

The point is that XPath support requires an extension when they went to all the trouble of implementing the others in the class.
<rhetorical>
It seems to me that all or most of {DescendantNodes, Descendants(), Descendants(XName), Element, Elements(), Elements(XName), ElementsAfterSelf(), ElementsAfterSelf(XName), ElementsBeforeSelf(), ElementsBeforeSelf(XName), Nodes, NodesAfterSelf, NodesBeforeSelf } can be implemented with XPath (and probably are) -- why not put the XPath method in the class and implement the others as Extensions?

I don't expect you to have the answer, of course, unless the answer is tequila.
PIEBALD goes off to look at the privates of an XContainer...

Richard Deeming 14-Aug-14 15:26pm

I suspect the Elements / Descendants / etc. are more LINQ-friendly than the XPath equivalents. This is LINQ to XML, after all!

There's still no built-in support for XPath 2.0 or XSL 2.0 in the latest version of .NET; they were initially talking about implementing XQuery[^], but I guess that got replaced by LINQ to XML, because I don't think it ever appeared.

PIEBALDconsult 14-Aug-14 15:40pm

I think they're more newbie-friendly, of the type that stunts their growth (like BASIC does :D ), but that's how I view all of Linq anyway.
When using an XmlNode, and its ilk, SelectNodes(String) does the heavy lifting, you don't really need anything else.
I suppose there may be people out there who take the same view of XPath as some do of Regular Expressions -- "now you have two problems".

Anshumaan Chaturvedi 14-Aug-14 15:46pm

Guys...chill... we solved it. :D Thanks for your support... I am learning something fruitful at last

PIEBALDconsult 14-Aug-14 16:16pm

"chill"

I'm in Phoenix; I never chill. :D

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Richard Deeming · Accepted Answer · 2014-08-14T08:46:00

Solution 2

The Element method[^] only looks for elements which are direct children of the specified node. It would find the <Summary> and <Detectors> elements, but won't work for the children of those elements.

Try using the Descendants method[^] instead:

C#

XElement findTag = xml.Descendants("Firmware_CRC").FirstOrDefault();

Posted 14-Aug-14 8:46am

Richard Deeming

Comments

Anshumaan Chaturvedi 14-Aug-14 14:50pm

thanks, it worked. So irrespective of what the root node is, it will eventually find the descendant node. Am i correct?

Richard Deeming 14-Aug-14 14:51pm

Yes - if the node you're looking for is anywhere underneath the root element, Descendants will find it.

If the node you're looking for might be the root node, then you'd use DescendantsAndSelf instead.