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

For me it was just Xcode not bothering to compile the code. Apple obviously doesn't think iOS development is complicated enough, so they have to build extra flakiness into the IDE.

I am told that SHIFT+COMMAND+K to clean the build can be a great help.