I posted about my question before in a different forum, but it bears repeating here. Xcode's code sense will sometimes not list what I want to type in. I think when it does, it's because such wording is already written in the file. I saw this behavior before while editing a different plaintext file, so I think Xcode is treating my Objective-C file as just another plaintext file.
I'll link to a screenshot later, but it's in the Apple Support Communities (look for a question with the same title as this thread's title.)