It appears that you're running Xcode on Mojave (which at this point is beta software), so I guess this could be a bug (seems like the labels are cut off). Have you tried to manually type your subclass name instead of choosing one?
– AlladinianSep 20 '18 at 10:16
yes,it is no problem to type subclass name,but it is troublesome without choosing one
– HH ZhengSep 20 '18 at 10:21
I agree. The best thing you can do is to report the bug (_Help > Report an Issue_) so it gets fixed before Mojave gets released.
– AlladinianSep 20 '18 at 10:22