Delegate methods are not called (transitioningDelegate)

Question

I'm trying to implement a custom transition between two viewControllers. (Swift 3.0)

Between my two viewControllers I have a UISegue with the kind show (animated = true).

So I set the delegate methods of UIViewControllerTransitioningDelegate in the extension of my first view controller :

extension DocumentsViewController : UIViewControllerTransitioningDelegate { ... }

And I also have implemented the required methods by the protocol :

animationController(forPresented presented: UIViewController, presenting: UIViewController, source: UIViewController) -> UIViewControllerAnimatedTransitioning? {
     ...
}

public func animationController(forDismissed dismissed: UIViewController) -> UIViewControllerAnimatedTransitioning? {
     ...
}

Now when the segue is perform, in the firstViewController I'm using the delegate method prepareForSegue to finally set the transitioningDelegate to my `secondViewController, see below :

public override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    super.prepare(for: segue, sender: sender)
    if let destination = segue.destination as? DocumentDetailViewController {
        destination.transitioningDelegate = self
    }
}

I check with breakpoints, the delegate is well setted to my firstViewController. But the delegate methods of transitioningDelegate in my firstViewController are never fired, I don't know why.

Any ideas ?

PS : In my storyboard, my segue have Animated to true, so this should work, but it doesn't.

Thanks.

SOLVED : A mix of MadreDeDios, Matt and Tushar answers.

1 : As I want to keep the navigation in my app, I have to make conform my first viewController to UINavigationControllerDelegate instead of UIViewControllerTransitioningDelegate. (see MadreDeDios answer's).

2 : According to this protocol, I have implemented the following delegate method :

public func navigationController(_ navigationController: UINavigationController, animationControllerFor operation: UINavigationControllerOperation, from fromVC: UIViewController, to toVC: UIViewController) -> UIViewControllerAnimatedTransitioning? {

...

}

3 : I set the delegate earlier at the viewDidLoad() of my firstViewController (see Matt's answer) :

override public func viewDidLoad() {
    super.viewDidLoad()
    //...
    self.navigationController?.delegate = self
}

4 : I'm using a manual push instead of a segue to display my secondViewController (see Tushar's answer).

Now this works, thank you.

Answer 1

The problem is that you are setting the transitioningDelegate too late. Way too late. It needs to be set very early in the lifetime of the view controller. I advise setting this property in the view controller's initializer.