Undefined symbols for architecture arm64:
  "_OBJC_CLASS_$_YYCache", referenced from:
      objc-class-ref in LFNetworking.o
  "_OBJC_CLASS_$_AFHTTPRequestSerializer", referenced from:
      objc-class-ref in LFNetworking.o
  "_OBJC_CLASS_$_AFJSONResponseSerializer", referenced from:
      objc-class-ref in LFNetworking.o
  "_OBJC_CLASS_$_AFHTTPSessionManager", referenced from:
      objc-class-ref in LFNetworking.o
ld: symbol(s) not found for architecture arm64

如果用CocoaPods匯入的庫，Build Setting->Linking->Other Linker Flags，新增$(inherited)