.net 4 xslt transformation Extension Function broken

Question

I\'m in the process of upgrading an asp.net v3.5 web app. to v4 and I\'m facing some problems with XSLT transformations I use on XmlDataSource objects.

Part of a XSLT fi

Answer 1

The problem seems to be that .NET 4.0 introduces an additional overload for HttpUtility.HtmlEncode. Up to .NET 3.5 there were the following overloads:

public static string HtmlEncode(string s);
public static void HtmlEncode(string s, TextWriter output);

.NET 4.0 also has the following method:

public static string HtmlEncode(object value);

This results in an XslTransformException:

(Ambiguous method call. Extension object 'ds:HttpUtility' contains multiple 'HtmlEncode' methods that have 1 parameter(s).

You probably don't see the exception because it is caught somewhere and not immediately reported.

Using .NET Framework classes as extension objects is a fragile thing as a new Framework version might break your transformation.

A fix would be to create a custom wrapper class and use that as extension object. This wrapper class may not have overloads with the same number of parameters:

class ExtensionObject
{
    public string HtmlEncode(string input)
    {
        return System.Web.HttpUtility.HtmlEncode(input);
    }
}

//...
XsltArgumentList arguments = new XsltArgumentList();
arguments.AddExtensionObject("my:HttpUtility", new ExtensionObject());