iOS swift facebook login button is not showing up if i don't use classForCoder

Question

I am trying to integrate Facebook single sign on to one of my iOS application. I have followed the instructions from Facebook and when i try to run the application i am getting the following error

Unknown class FBSDKLoginButton in Interface Builder file.

After searching on web, i found that adding the following code will resolve the issue.

FBSDKLoginButton.classForCoder()

My question is, what is the significant of this code? What does this perform behind the scene?

Answer 1

From Apple's Foundation Framework Reference :

classForCoder is a property Overridden by subclasses to substitute a class other than its own during coding. (read-only) Overridden by subclasses to substitute a class other than its own during coding. (read-only)

This method is invoked by NSCoder. NSObject's implementation returns the receiver's class. The private subclasses of a class cluster substitute the name of their public superclass when being archived.

Declaration :

var classForCoder: AnyClass { get }