cocoa - _OBJC_CLASS referenced from objc-class-ref in AppDelegate.o -

i trying set toolbar opens various windows according toolbar item user selects. each window has own xib file , own subclass of nswindowcontroller. have not made changes window controllers' h , m files. switch in appdelegate implementation file reads selected toolbar item's tag , allocs appropriate window controller, passes initwithwindownibname message. problem of windows work , others produce "undefined symbol" error regarding window controller's class name. have double checked imports , looked typos. difference i've spotted in window controller implementation files work, line "@interface windowcontrollername ()" recognizes windowcontrollername class name , colors blue, in files not work, remains black. have no idea causes difference.

i have solved problem , posting answer, should else. did not have target's "target membership" checkbox checked in window controllers' implementation files. rookie error, guess.