iOS - keyboardWillShow: unrecognized selector sent to instance

Question

In my application I am adding following observer in init method of class A.


 [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(keyboardWillShow:)
                                                 name:UIKeyboardWillShowNotification
                                               object:nil];
 [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(keyboardWillHide:)
                                                 name:UIKeyboardWillHideNotification
                                               object:nil];

Then I am extending a class B from class A. keyboardWillShow and keyboardWillHide methods are written in super class i.e. class A. However application throws following exception when I click on some textview to enter text.

terminating app due to uncaught exception 'NSInvalidArgumentException',
reason: '-[B   keyboardWillShow:]: unrecognized selector sent to instance xyz'

It is confuses as methods are already written in the supper class of B. If it is due to invalid arguments, then how can it be as arguments are passing by iOS itself.

Answer 1

It's hard to tell from just that bit of code, but it looks like you have an error in your method names. In the code you provided, you are registering for the notifications with a method named "keyboardWillToggle:". The error is indicating that you are trying to call a "keyboardWillShow:" method, though.

It would probably be best to declare and implement "keyboardWillShow:" and "keyboardWillHide:" on your class A, and then register for the notifications like this:

 [[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(keyboardWillShow:)
                                             name:UIKeyboardWillShowNotification
                                           object:nil];
 [[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(keyboardWillHide:)
                                             name:UIKeyboardWillHideNotification
                                           object:nil];

Answer 2

It appears you need to declare/define the method named keyboardWillShow: in your class.

Answer 3

This just happened to me, and the methods do exist, but they are not declared in my .h file. Meaning, the method should be public that is accessible by the NSNotificationCenter.

Answer 4

The reason why is failing is because you do not have implemented those methods in the new controller where you find yourself. Once you leave that controller you have to remove those observers. Otherwise in whatever other controller when you will need to use the keyboard those observes will be triggered and they will search for those methods in your class but if you do not have them defined it will throw that error you describe.