Error message in XSLT with C# extension function

Question

I am received the following error while trying to implement a C# extension function in XSLT.

Extension function parameters or return values which have

Answer 1

XSLT extension methods must return a type that is supported within XSL transformations. The following table shows the W3C XPath types and their corresponging .NET type:

W3C XPath Type        | Equivalent .NET Class (Type)
------------------------------------------------------
String                | System.String
Boolean               | System.Boolean
Number                | System.Double
Result Tree Fragment  | System.Xml.XPath.XPathNavigator
Node Set              | System.Xml.XPath.XPathNodeIterator

The table is taken from the section Mapping Types between XSLT and .NET in this MSDN Magazine article.

Instead of returning a string[] array you would have to return an XPathNodeIterator like it is done in the following example:

In your XSL transform you can then iterate over the elements in the returned node set using xsl:for-each: