Question

I have the following in my xslt file:

<xsl:param name="predicate" select="//Event" />
<xsl:apply-templates select="$predicate" />

And this works fine, but now I’d like to change the param from my .net code.

var args = new XsltArgumentList();
args.AddParam("predicate", "", "//Event[@valid]");
xmlviewer.TransformArgumentList = args;

but no matter what i pass in for predicate, I get the error “Expression must evaluate to a node set.”

Is there a way to pass the xpath selector into the transform?

Answer 1

args.AddParam("predicate", "", "//Event[@valid]");

You are passing just a string to the stylesheet, but the stylesheet is using the predicate parameter as a node-set — it performs an <xsl:apply-templates> on it.

The solution

Evaluate the XPath expression you are now passing as a string. For example, use the Select() method of XPathNavigator. Then pass as parameter to the transformation the resulting XPathNodeIterator.