Changing navigation bar (menue) back button title in run time.

Hello there, I'm as of now dealing with changing route bar back button in run time. Anyway it doesn't work. The following is the code where I need to change my back button title. What I maintain that should do is to make my backButton title to be "back", else " ". The strategy for changing back button title appears to work in the initial time when the view loads up, however doesn't change all things considered. Is it to change back Fasten title in run time? supersede func scrollViewDidScroll(_ scrollView: UIScrollView) { let a = tableView.tableHeaderView?.subviews[1]

let heightCheck = tableView.bounds.origin.y + a!.frame.height + navigationController!.navigationBar.frame.height
var backButtonTitle = " "

if heightCheck > a!.frame.origin.y{
  backButtonTitle = "back"
}else{
  backButtonTitle = " "
}

navigationController?.navigationBar.topItem?.backButtonTitle = backButtonTitle

}