Delegate methods are not called (transitioningDelegate) - ios

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.

Answer 2

Because you are using a push segue, I assume you are using a navigation controller as well.
When you are using an UINavigationController, it becomes the reference for every transition, animation, and even your app's orientation.
My advice would be to use your navigation controller as the manager for all your animations. All you need to do is to add these few things:
extension MyNavigationController: UINavigationControllerDelegate {
func navigationController(_ navigationController: UINavigationController, animationControllerFor operation: UINavigationControllerOperation, from fromVC: UIViewController, to toVC: UIViewController) -> UIViewControllerAnimatedTransitioning? {
//Check for the good animation
return MyAnimation()
}
}
And inside your MyNavigationController class
override func viewDidLoad() {
super.viewDidLoad()
//This is the key
self.delegate = self
//Only if you want to animate the presentation of your navigation controller itself, the first time it appears:
self.transitioningDelegate = self
}

Answer 3

Try removing the transition of storyboard and execute the view presentation code manually and explicitly mention 'true' for the animated parameter :
presentViewController(documentVC, animated: true, completion: nil)