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

It means, method is not defined or on the other-way, calling a method on the wrong object.

classic example of this error is missing of ':' in selector call.

UIBarButtonItem *doneBtn = [[UIBarButtonItem alloc]
initWithBarButtonSystemItem:UIBarButtonSystemItemDone target:self
                action:@selector(DatePickerDoneClick)];

Here,

action:@selector(DatePickerDoneClick:)

is expected rather than

action:@selector(DatePickerDoneClick)