ios - Admob Reward Video GADRewardBasedVideoAdDelegate Undefined symbols -

i implemented admob (ver 7.9.1) reward video based on tutorial: https://firebase.google.com/docs/admob/ios/rewarded-video

but can not compile app feature. i'm getting error:

undefined symbols architecture x86_64:   "l_objc_protocol_$_gadrewardbasedvideoaddelegate", referenced from:       l_objc_class_protocols_$_viewcontroller in libframework.a(viewcontroller.o) ld: symbol(s) not found architecture x86_64 clang: error: linker command failed exit code 1 (use -v see     invocation) 

i implemented banner , interstitial ads , worked fine.

any suggestions?

importing googlemobileads/gadrewardbasedvideoaddelegate.h , working.

#import <googlemobileads/gadrewardbasedvideoaddelegate.h>