Question

I need to read an xml element which has attribute xmlns=”http://www.w3.org/2000/09/xmldsig#”.
XPathSelectElement is giving error “Object reference not set to an instance of an object.”

Here is the sample code.

var xml = "<root><tagA>Tag A</tagA><tagB>Tag B</tagB></root>";
XDocument xd = XDocument.Parse(xml);
var str = xd.XPathSelectElement("/root/tagB").ToString(SaveOptions.DisableFormatting);
Console.WriteLine(str);

The result of the above code is:

<tagB>Tag B</tagB>

If I put attribute,

var xml = "<root><tagA>Tag A</tagA><tagB xmlns=\"http://www.w3.org/2000/09/xmldsig#\">Tag B</tagB></root>";

I got error.

Object reference not set to an instance of an object.

Am I missing something here? Can anyone please help me out. (I know I can get by using other methods. I just want to know what I am missing here)

Thank you very much.

Answer 1

You can register the element’s namespace in an XmlNamespaceManager:

XmlNamespaceManager nsmgr = new XmlNamespaceManager(new NameTable());
nsmgr.AddNamespace("ns", "http://www.w3.org/2000/09/xmldsig#");

var str = xd.XPathSelectElement("/root/ns:tagB", nsmgr)
            .ToString(SaveOptions.DisableFormatting);
Console.WriteLine(str);