Xcode code sense seems to think an Objective-C file is a plain-text file

I'm having a bit of a problem. You know how when you type in the first few letters of a method you want to use in your code and Xcode helpfully autocompletes the code and lets you enter your parameters simply by hitting "tab", or clicking blue rounded rectangles, and typing them in? Well, that's not happening. I type in a method and Xcode will sometimes autocomplete the first part of the the method's name, but nothing more. Xcode seems to be acting as if I am editing a plaintext file and not an Objective-C file, even though the file ends in .m and looks like an Objective-C file.

Here's a picture of what I see:

 

OK, the problem seems to have gone away on its own.