extension allows to handle UINavigationViewController's 'Back' button action, migrate from https://github.com/onegray/UIViewController-BackButtonHandler

UINavigationBarBackButtonHandler.swift

//
//  UINavigationBarBackButtonHandler.swift
//  Demo
//
//  Created by HamGuy on 20/04/2017.
//  Copyright © 2017 hamguy.net. All rights reserved.
//

import Foundation


/// Handle UINavigationBar's 'Back' button action
protocol  UINavigationBarBackButtonHandler {
    
    /// Should block the 'Back' button action
    ///
    /// - Returns: true - dot block，false - block
    func  shouldPopOnBackButton() -> Bool
}

extension UIViewController: UINavigationBarBackButtonHandler {
    //Do not block the "Back" button action by default, otherwise, override this function in the specified viewcontroller
    func  shouldPopOnBackButton() -> Bool {
        return true
    }
}

extension UINavigationController: UINavigationBarDelegate {
    public func navigationBar(_ navigationBar: UINavigationBar, shouldPop item: UINavigationItem) -> Bool{
        guard let items = navigationBar.items else {
            return false
        }
        
        if viewControllers.count < items.count {
            return true
        }
        
        var shouldPop = true
        if let vc = topViewController, vc.responds(to: #selector(UIViewController.shouldPopOnBackButton)){
            shouldPop = vc.shouldPopOnBackButton()
        }
        
        if shouldPop{
            DispatchQueue.main.async {
                self.popViewController(animated: true)
            }
        }else{
            for aView in navigationBar.subviews{
                if aView.alpha > 0 && aView.alpha < 1{
                    aView.alpha = 1.0
                }
            }
        }
        return false
    }
}


/// Use age 

class SomeController: UIViewController{
  /**
  ......
  do something
  */
  
  override func shouldPopOnBackButton() -> Bool {
        /**
          do something
          return false/true
        */
    }

    
    // Handle the pop gesture
    override func willMove(toParentViewController parent: UIViewController?) {
        if parent == nil { // When the user swipe to back, the parent is nil
            do something
            return
        }
        super.willMove(toParentViewController: parent)
    }
}

I used objective c code it's working fine....

not working