UINavigationController extension to fix back swipe when having custom back button

UINavigation+Extension.swift

extension UINavigationController: UINavigationControllerDelegate, UIGestureRecognizerDelegate {
    
    public override static func initialize() {
        struct Static {
            static var token: dispatch_once_t = 0
        }
        
        if self !== UINavigationController.self {
            return
        }
        
        dispatch_once(&Static.token) {
            
            // Swizzle viewDidLoad
            
            self.swizzleViewDidLoad()
            
            // Swizzle pushViewController
            
            self.swizzlePushController()
        }
    }
    
    // MARK: - Helpers
    
    static func swizzleViewDidLoad() {
        let originalViewDidLoadSelector = #selector(UINavigationController.viewDidLoad)
        let swizzledViewDidLoadSelector = #selector(UINavigationController.newViewDidLoad)
        
        let originalViewDidLoadMethod = class_getInstanceMethod(self, originalViewDidLoadSelector)
        let swizzledViewDidLoadMethod = class_getInstanceMethod(self, swizzledViewDidLoadSelector)
        
        let didAddViewDidLoadMethod = class_addMethod(self, originalViewDidLoadSelector, method_getImplementation(swizzledViewDidLoadMethod), method_getTypeEncoding(swizzledViewDidLoadMethod))
        
        if didAddViewDidLoadMethod {
            class_replaceMethod(self, swizzledViewDidLoadSelector, method_getImplementation(originalViewDidLoadMethod), method_getTypeEncoding(swizzledViewDidLoadMethod))
        } else {
            method_exchangeImplementations(originalViewDidLoadMethod, swizzledViewDidLoadMethod);
        }
    }
    
    static func swizzlePushController() {
        let originalPushControllerSelector = #selector(UINavigationController.pushViewController(_:animated:))
        let swizzledPushControllerSelector = #selector(UINavigationController.newPushViewController(_:animated:))
        
        let originalPushControllerMethod = class_getInstanceMethod(self, originalPushControllerSelector)
        let swizzledPushControllerMethod = class_getInstanceMethod(self, swizzledPushControllerSelector)
        
        let didAddPushControllerMethod = class_addMethod(self, originalPushControllerSelector, method_getImplementation(swizzledPushControllerMethod), method_getTypeEncoding(swizzledPushControllerMethod))
        
        if didAddPushControllerMethod {
            class_replaceMethod(self, swizzledPushControllerSelector, method_getImplementation(originalPushControllerMethod), method_getTypeEncoding(swizzledPushControllerMethod))
        } else {
            method_exchangeImplementations(originalPushControllerMethod, swizzledPushControllerMethod);
        }
    }
    
    // MARK: - Method Swizzling
    
    func newViewDidLoad() {
        self.newViewDidLoad()
        
        self.interactivePopGestureRecognizer?.delegate = self
        self.delegate = self
    }
    
    func newPushViewController(viewController: UIViewController, animated: Bool) {
        self.interactivePopGestureRecognizer?.enabled = false
        
        self.newPushViewController(viewController, animated: animated)
    }
    
    // MARK: - UINavigationControllerDelegate
    
    public func navigationController(navigationController: UINavigationController, didShowViewController viewController: UIViewController, animated: Bool) {
        self.interactivePopGestureRecognizer?.enabled = true
    }
}