If you are using Objective-C++ (i.e. mix Objective-C with C++ code) then refactoring is disabled in xcode since it does not support refactoring of C++ code.
For me I realized Refactor was disabled because the Xcode project I had opened was referencing a Base SDK that was missing. Edit Project Settings and in the Build tab set the Base SDK to one that you have (like for me this was iOS 4.2). This enabled Refactor for me.
Also, it could happen that you renamed the filename for the class, either outside xcode or by ctrl-clicking the filename and then renaming it.
xcode refuses to refactor if filename does not match with the class name.
Had this problem as well. I ran through trying to find missing SDKs, saving files, and looking for Objective-C++ code as mentioned above, and all it took to fix my machine was rebooting XCode.
I've been using Xcode for 5 years now, and refactoring has never worked correctly (even xcode 4.6 has major bugs where it WILL corrupt your source code!).
The workaround has always been (still works 100%, even in cases where Apple's code fails)
use shift-command-f to find all uses of the file
select "replace" in the search settings
"replace-all"
do the following for the .h file, and REPEAT IT FOR THE .m FILE (if you have one):
right click the original file, and select "show in finder"
delete the file from xcode (select "delete references only" when asked)
rename the .h (and .m if you have one) in Finder
in Xcode, select "Product -> (hold down Alt) -> Clean Build Folder"
quit xcode (you can usually get away with not doing this - but NOTE: there are some other MAJOR bugs in Xcode where it crashes itself if you don't do this)
re-open xcode
drag/drop the .h and .m back into Xcode
wait a few seconds (some of Xcode's core methods are asynchronous - allowing it to corrupt your project)
finally, when it seems to be doing nothing (and your hard disk isn't making any noise any more): cmd-b to re-build
I have a 100% success rate with this method. I just tried refactoring with Apple's "Refactor -> Rename" in latest xcode and it failed - again!
(this time with the incorrect error: "Unable to determine the language of", one of those error messages where Apple put the wrong text in place)
This may be a bit late, but I stumbled across this post because I was unable to refactor my "ViewController.swift" file to "WhateverViewController.swift". I tried selecting the file in the Project Navigator and then selecting "Editor -> Refactor" from the top menu, but 'rename' is always greyed out.
Instead, what worked was selecting the ViewController name from the editor. So if you have:
class ViewController: UIViewController {
// Code here...
}
Highlight the "ViewController" word and then select Refactor from the menu or right-click and select Refactor -> rename.