Описание тега unrecognized-selector

"Unrecognized selector" is an exception in Cocoa and Cocoa Touch, thrown when an object receives a message to which it cannot respond.

This most often means that the object is not of the expected class. For example,

NSDictionary * d = @{@"item_code" : @45};
NSString * code = d[@"item_code"];
NSLog(@"%@", [code uppercaseString]);

will raise this exception, saying

-[__NSCFNumber uppercaseString:]: unrecognized selector sent to instance 0x9028390

because the object is an NSNumber, not an NSString despite the type of the pointer.

For useful debugging procedures, see /questions/45638039/kak-ya-mogu-otladit-oshibku-neraspoznannyij-selektor-otpravlen-v-ekzemplyar