What does the error “unrecognized selector sent to instance” mean in Xcode

Question

What does it mean \"unrecognized selector sent to instance\" in Xcode?

Answer 1

I think this error is due to calling a function in class which is not declared in the class.

Answer 2

There are several reasons why this can occur:

ONE:The method is declared in the .h, but does not exist in the .m. The compiler does not complain, but during execution you face that crash.Please,Check this out:

1. The method is implemented in the m.
2. The method signature is exactly the same.
3. There is not a semi-colon at the end of the method signature.

TWO:If you are calling a delegated method, check if this method is really implemented.

I use to have this error when I modify the signature, but I forgot to update the signature method on the implementation file .m

Answer 3

I had a similar problem and the issue was my ".m" class containing the unknown selector wasn't in the "Build Phases / Compile Sources" list. I added it and everything was fixed.

Answer 4

It means that you have called a method on an object which does not support that method.

The reason it says 'unrecognised selector' is that method invocation is implemented by a message sending mechanism. The part of the message that contains the method name is called the selector.