UINavigationControllerDelegate method call crash

[marcin-zbijowski]

I'm working on an app that incorporates WYPopoverController and it works great in place where it should. I want to add custom animations between two controllers, instead of built in push / pop.

In navigation controller containing FROM and TO controllers I don't do anything related to the WYPopoverController, neither in controllers FROM and TO.

I've implemented navigation controller delegate, really simple and animator class that handles actual animation.

public class NavigationControllerDelegate: NSObject, UINavigationControllerDelegate {

    let animator = Animator()

    public func navigationController(navigationController: UINavigationController, animationControllerForOperation operation: UINavigationControllerOperation, fromViewController fromVC: UIViewController, toViewController toVC: UIViewController) -> UIViewControllerAnimatedTransitioning? {

        if operation == UINavigationControllerOperation.Pop {
            return self.animator
        }

        return nil
    }
}

class Animator: NSObject, UIViewControllerAnimatedTransitioning {

    public func transitionDuration(transitionContext: UIViewControllerContextTransitioning) -> NSTimeInterval {
        return 0.33
    }

    public func animateTransition(transitionContext: UIViewControllerContextTransitioning) {
        let toVC = transitionContext.viewControllerForKey(UITransitionContextToViewControllerKey)!
        let fromVC = transitionContext.viewControllerForKey(UITransitionContextFromViewControllerKey)!

        transitionContext.containerView().addSubview(toVC.view)
        toVC.view.alpha = 0

        UIView.animateWithDuration(self.transitionDuration(transitionContext), animations: { () -> Void in
            fromVC.view.transform = CGAffineTransformMakeScale(0.1, 0.1)
            toVC.view.alpha = 1
        }) { (finished) -> Void in
            fromVC.view.transform = CGAffineTransformIdentity
            transitionContext.completeTransition(!transitionContext.transitionWasCancelled())
        }
    }

}

In the FROM controller I initialize navigation delegate

override public func viewDidLoad() {
    super.viewDidLoad()
    // ... some other code here
    self.navigationController?.delegate = NavigationControllerDelegate()
}

Everything compiles and runs up until the point when I tap the (collection) cell and want to move to TO controller. At that point app crashes with error:

-[CALayer navigationController:animationControllerForOperation:fromViewController:toViewController:]: unrecognized selector sent to instance 0x7fc72e53e970

I've added a breakpoint and I end up inside sizzled_pushViewController:animated: method of UINavigationController. To be honest I have no idea how to approach the issue.