iOS 这是什么问题

Undefined symbols for architecture x86_64:
  "_OBJC_CLASS_$_EMMessage", referenced from:
      objc-class-ref in ChatSendHelper.o
      objc-class-ref in InitDataViewController.o
  "_OBJC_CLASS_$_EMTextMessageBody", referenced from:
      objc-class-ref in ChatSendHelper.o
      objc-class-ref in InitDataViewController.o
  "_OBJC_CLASS_$_EMConversation", referenced from:
      objc-class-ref in ContactsViewController.o
  "_OBJC_CLASS_$_EMImageMessageBody", referenced from:
      objc-class-ref in ChatSendHelper.o
  "_OBJC_CLASS_$_EMVideoMessageBody", referenced from:
      objc-class-ref in ChatViewController.o
  "_OBJC_CLASS_$_EMVoiceMessageBody", referenced from:
      objc-class-ref in ChatViewController.o
  "_OBJC_CLASS_$_EMOptions", referenced from:
      objc-class-ref in AppDelegate+EaseMob.o
  "_OBJC_CLASS_$_EMClient", referenced from:
      objc-class-ref in ChangyongfangDetailController.o
      objc-class-ref in AppDelegate.o
      objc-class-ref in HasIssuedViewController.o
 
      ...
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)