Easiest way to check if an arbitrary String is a valid filename

Question

In my application the user can enter a filename. Before processing I'd like to check if the input String is a valid filename on Windows Vista.

Whats the easiest way to do that?

By valid I'm reffering to legal and non-existing

Answer 1

Check whether filename.IndexOfAny(Path.GetInvalidFileNameChars()) < 0 and !File.Exists(Path.Combine(someFolder, filename))

Answer 2

Check against GetInvalidFileNameChars():

var isValid = !string.IsNullOrEmpty(fileName) &&               fileName.IndexOfAny(Path.GetInvalidFileNameChars()) < 0 &&               !File.Exists(Path.Combine(sourceFolder, fileName));