I was recently updating an app cerated a long time ago and I opened it in Xcode 6 hit run. Once the app launched I got an error that said “Unknown class <ClassDelegate> in Interface Builder file.”

After reading through a number of suggestions of what to try, most of which were fixes for if you are using a storyboard (which I wasn’t), I found that in the didFinishLaunchingWithOption if you put [<ClassDelegate> class] then this removed the error.