Get element using XName in XML

Question

I have an XML file which looks like this, the call out is that namespace uses prefix, xmlns:opf.

<?xml version="1.0" encoding="utf-8"?>  
<package version="2.0" unique-identifier="uuid_id" xmlns:opf="http://www.idpf.org/2007/opf">  
    <metadata xmlns:dcterms="http://purl.org/dc/terms/">  
    </metadata>  
</package>  

Following is my code trying to get the 'package' element using the XName

static void Main(string[] args)  
{  
    using (MemoryStream stream = new MemoryStream(File.ReadAllBytes(@"C:\Users\xyz\Downloads\XMLs\X2.xml")))  
    {  
        XDocument xDoc = XDocument.Load(stream);  
        XNamespace opfNamespace = "http://www.idpf.org/2007/opf";  

        XElement packageElement = xDoc.Element(opfNamespace + "package");  

        Console.WriteLine($"packageElement is null - {packageElement == null}");  
        Console.WriteLine($"Prefix - [{xDoc.Root.GetPrefixOfNamespace(opfNamespace)}] Namespace - [{xDoc.Root.GetNamespaceOfPrefix("opf")}]");  
  
        foreach (var element in xDoc.Elements())  
        {  
            Console.WriteLine($"Element: Namespace - [{element.Name.NamespaceName}] Name - [{element.Name.LocalName}]");  
        }  
    }  
}  

The output of the program is -

packageElement is null - True  
Prefix - [opf] Namespace - [http://www.idpf.org/2007/opf]  
Element: Namespace - [] Name - [package]  

So, it's not able to find the element using opfNamespace + "package", for further debugging I logged the elements, and it shows that the element.Name does not contain the namespace, which explains why it's not able to find element using opfNamespace + "package".

Question - How do I find the 'package' element from the above XML, I don't want to iterate through all the elements manually?

Is the XML parsing happening correctly, and the 'package' element not having namespace is expected?

For further testing, I removed the prefix from the namespace and ran the code, this time it's able to find the 'package' element.

XML -

<?xml version="1.0" encoding="utf-8"?>  
<package version="2.0" unique-identifier="uuid_id" xmlns="http://www.idpf.org/2007/opf">  
    <metadata xmlns:dcterms="http://purl.org/dc/terms/">  
    </metadata>  
</package>  

Output -

packageElement is null - False  
Prefix - [] Namespace - []  
Element: Namespace - [http://www.idpf.org/2007/opf] Name - [package]  

Answer 1

The reason you'd want to prefix the value you pass to .Element() with a namespace is if that element actually had a namespace. i.e. here you're defining the namespace (via the xmlns attribute) that you can use to prefix package and it's descendants:

   <package version="2.0" unique-identifier="uuid_id" xmlns:opf="http://www.idpf.org/2007/opf">  

Although this statement won't find if because it'll be looking for <opf:package> instead of <package>:

   XElement packageElement = xDoc.Element(opfNamespace + "package");  

Remove the opfNamespace + from the line above (or add the opf: prefix to <package> in your XML) and it should find it.

If you defined the xmlns attribute like this: xmlns="http://www.idpf.org/2007/opf" then the default namespace would become the opf namespace, meaning all your references to elements in or under that declaration in the XML file would automatically have an opf namespace, so you'd always have to prefix that to your element names.