Question

What is the more efficient way to check an XmlDocument for an XmlDeclaration node?

Answer 1

What sort of “efficiency” are you after? Efficiency of expression, or efficiency at execution time? Here’s a LINQ query which finds the declaration pretty quickly:

XmlDeclaration declaration = doc.ChildNodes
                                .OfType<XmlDeclaration>()
                                .FirstOrDefault();

I strongly suspect that will be efficient enough. It’s possible that you could just test whether the first child node was an XmlDeclaration… I don’t think anything else can come before it.

If there’s any possibility of using LINQ to XML instead, then it becomes even easier – you just use the XDocument.Declaration property.