A small extension to demonstrate how to use selectorCallback

SelectorDemoViewController.swift

class SelectorDemoViewController: UIViewController {
    
    override func viewDidLoad() {
        NotificationCenter.default.addObserver(self,
                                               selector: selector,
                                               name: kUnwindNotification,
                                               object: nil)
    }
}

extension SelectorDemoViewController {

    override func selectorCallback(_ sender: Any) {
        if let button = (sender as? UIButton) {
            unwindWebView(button)            
        }
    }
    
}