XCode - Classes folder set aside

I have lost my classes folder in Xcode and have disco开发者_C百科vered it has been 'Set Aside' and called Classes-1. How on earth did this happen and how do I undo it. There is no Classes folder in my project at all now and Classes-1 doesn't show up in XCode, only Finder. I can do nothing with the project at all except restore to a previous snapshot.

Help me please.

Create a group in Xcode - call it Classes. Add all files back again.