How to Use XPath with Default Namespaces in C#?

Working with XPath and Default Namespaces in C#

XML documents often utilize default namespaces. When querying such documents using XPath, correctly handling these namespaces is crucial for accurate node selection. Failure to specify the namespace will likely result in empty query results.

The XmlNamespaceManager class provides the solution. It allows you to define namespaces and associate them with prefixes, enabling proper XPath queries. Here's a C# implementation:

XmlElement el = ...; // Your root XML element
XmlNamespaceManager nsmgr = new XmlNamespaceManager(el.OwnerDocument.NameTable);
nsmgr.AddNamespace("x", el.OwnerDocument.DocumentElement.NamespaceURI);
XmlNodeList nodes = el.SelectNodes("/x:outerelement/x:innerelement", nsmgr);

Explanation:

• el: Represents the root element of your XML document.
• XmlNamespaceManager: Created using the document's NameTable.
• nsmgr.AddNamespace("x", ...): Adds a namespace with the prefix "x," mapping it to the namespace URI of the root element. This prefix will be used in the XPath expression.
• el.SelectNodes(...): Executes the XPath query using the nsmgr to resolve namespace prefixes. The XPath expression /x:outerelement/x:innerelement now correctly identifies elements within the default namespace.

This approach ensures that your XPath expressions accurately target nodes within the default namespace, providing the correct results. Remember to replace /x:outerelement/x:innerelement with your specific XPath expression.

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