I want to sort an array of NSStrings by length, but then have all strings that are the same length be sub-sorted alphabetically. For example, "cat, hat, zen, nine, rate, tale, access, vanish."

How can I do this? I've been trying to figure out NSSortDescriptors for like an hour and gotten nowhere. I do not know what keys to use in order to sort NSStrings alphabetically or by length. I have sorted them alphabetically using `sortedArrayUsingSelector`, but over KevinTTrimm's comment's link, I need to use NSSortDescriptor in order to sort by two metrics, so I need to know the keys.