xcode - open - Unknown Window class(null) in Interface Builder file, creating generic Window instead
swift open window (3)
My app uses storyboards and the windows have to use a custom class,
MyWindow for example, or at runtime/launching the app, there is an error message saying:
Unknown Window class (null) in Interface Builder file, creating generic Window instead
I just noticed this after upgrading to Xcode 9.1, but I'm not sure if it was there before.
A similar question is here: Xcode 6 Strange Bug: Unknown class in Interface Builder file
My other project doesn't have this issue. I will investigate it later.
In both projects, a window is owned by a custom window controller. I checked the storyboard xml but didn't find anything odd.
This is solved in the newest XCode update 9.3 (9E145)
Fixed an issue compiling macOS storyboards that resulted in incorrectly logging: "Unknown Window class (null) in Interface Builder file, creating generic Window instead." (34994636)
I had the same issue after upgrading to Xcode 9.1. To resolve the error you need to replace all instances of NSWindow in storyboards with custom subclasses of NSWindow.
This warning also occurs when I build and run a brand new empty project in Xcode 9.1.
Replacing the default NSWindow with an empty custom class of NSWindow with no changes does remove the error, but that behaviour makes no sense.
Therefore, I'm filing it as a bug.