Cause of the abnormality unrecognized selector of the newspaper?
objc When sending a message to an object, Runtime Library finds actually belongs to the object class in accordance with isa object pointer, and then to find a method in the process of running the class list and a list of its parent class, method, if, at the top level of when the parent class still can not find the appropriate way, will enter the stage of message forwarding, three times if the message forwarding process remains unfulfilled, the program will hang at run time and throws an exception unrecognized selector sent to XXX.