I understand where the decision to use "NS" as a class prefix came from, but you should really reconsider that choice. Yeah, yeah, I understand that Swift mangles your class name, but it's still a pretty bad idea.
It is not just a poor choice but actually wrong - when overriding Objc classes and doing namespace prefixing like this, two-letter codes (like NS and UI and CI) are reserved by Apple. Third party code should use three-letter prefixes.