'Use of Unresolved Identifier' in Swift

Sometimes the compiler gets confused about the syntax in your class. This happens a lot if you paste in source from somewhere else.

Try reducing the "unresolved" source file down to the bare minimum, cleaning and building. Once it builds successfully add all the complexity back to your class.

This has made it go away for me when re-starting Xcode did not work.

One possible issue is that your new class has a different Target or different Targets from the other one.

For example, it might have a testing target while the other one doesn't. For this specific case, you have to include all of your classes in the testing target or none of them.

'Use of Unresolved Identifier' in Swift my also happen when you forgot to import a library. For example I have the error:

In which I forgot the UIKit

import UIKit

Once I had this problem after renaming a file. I renamed the file from within Xcode, but afterwards Xcode couldn't find the function in the file. Even a clean rebuild didn't fix the problem, but closing and then re-opening the project got the build to work.