iOS [__nscfnumber isequaltostring:]: Unrecognized selector sent to instance 0x7a97d4c0 ' error

Today the interface from get to post, I went to change the login but there is a mistake, first of all to see if you can interact with the server, can get data, and secondly, the data obtained is not what you want, remember, the first mistake to think of their own problems, there is a program to learn to solve their own, break point to find the reason , step by step, and see where the problem is.

My question is to take the Nscfnumber type and nsstring type to make a comparison, because will not respond to the Isequaltostring method and error, so as long as the conversion can be

NSString *factory_id = [NSString stringwithformat:@ "%@", [Response objectforkey:@ "factory_id"]];

iOS [__nscfnumber isequaltostring:]: Unrecognized selector sent to instance 0x7a97d4c0 ' error