Check when back button has been pressed

Back button tapped

public override func viewWillDisappear(animated: Bool) {
    if let navigationStackViewControllers = self.navigationController?.viewControllers {
        if navigationStackViewControllers.contains(self) == false {
            // View controller has been popped as it is not in navigation stack any more
        }
    }
    
    super.viewWillDisappear(animated)
}