在AppDelegate.o中引用object -class-ref的_OBJC_CLASS

I am trying to set up a toolbar which opens various windows according to the toolbar item the user selects. Each window has its own xib file and its own subclass of NSWindowController. I have not made any changes to the window controllers' h and m files. A switch in the AppDelegate implementation file reads the selected toolbar item's tag and allocs the appropriate window controller, then passes it the initWithWindowNibName message. The problem is that some of the windows work and others produce an "undefined symbol" error regarding their window controller's class name. I have double checked all imports and looked for typos. The only difference I've spotted is that in the window controller implementation files that do work, the line "@interface WindowControllerName ()" recognizes WindowControllerName as a class name and colors it blue, but in the files that do not work, it remains black. I have no idea what causes this difference.I am trying to set up a toolbar which opens var