Swift - ABAddressBookRegisterExternalChangeCallback
<p>I am trying to register an address book change callback in swift but can't seem to find how to do it. I know how do get a notification on address book change for iOS 9 but I need for iOS 8 as well.</p>

<pre><code>    if #available(iOS 9.0, *)
    {
        NSNotificationCenter.defaultCenter().addObserver(self, selector: "addressBookDidChange:", name: CNContactStoreDidChangeNotification, object: nil)
    }
    else
    {
        // What goes here?
    }
</code></pre>

<p>I do understand I need to use <code>ABAddressBookRegisterExternalChangeCallback</code> but I can't find a way how to call a function from it.</p>

<p>Thank You for any help</p>