Custom Segue in Swift 2.0 : destinationViewController's navigationController property returning nil

Question

I have a segue from ViewController A to ViewController B. It uses a custom segue class RightSegue. This is the code for the RightSegue class:

class RightSegue: UIStoryboardSegue {

override func perform() {

    // Assign source and destination view controllers to local variables.
    let vc1: UIViewController = self.sourceViewController
    let vc2: UIViewController = self.destinationViewController

    // Get screen width and height.
    let screenWidth = UIScreen.mainScreen().bounds.size.width
    let screenHeight = UIScreen.mainScreen().bounds.size.height

    // get the source view controller's frame.
    let vc1Frame = vc1.view.frame

    let vc2NavController = vc2.navigationController
    let vc2NavFrameHeight = vc2NavController!.navigationBar.frame.size.height

    // Specify the initial position of the destination view. (x, y, width, height)
    vc2.view.frame = CGRectMake(screenWidth, vc2NavFrameHeight, screenWidth, screenHeight)

    // Push the destinationViewController onto sourceViewController.
    vc1.navigationController!.pushViewController(vc2, animated: false)

    // Specify the initial position of the source view. Add destination view as a subview of the source view.
    vc1.view.frame = CGRectMake(vc1.view.frame.origin.x, vc1.view.frame.origin.y, screenWidth, vc1Frame.size.height)
    vc2.navigationController?.view!.addSubview(vc1.view!)

    // Animate!
    UIView.animateWithDuration(0.25, animations: {() -> Void in

        vc1.view.frame = CGRectMake(-screenWidth, vc1.view.frame.origin.y, vc1.view.frame.size.width, vc1.view.frame.size.height)
        vc2.view.frame = CGRectMake(0.0, 0.0, vc2.view.frame.size.width, vc2.view.frame.size.height)

        }, completion: {(finished: Bool) -> Void in

            vc1.view!.removeFromSuperview()

    })

}

The view controllers are set up as shown in the image.

As can be seen, the FirstViewController contains a button which when clicked shows the SecondViewController.

The next image shows the segue's properties:

When I execute the app and press the button in FirstViewController, the app crashes with the error message:

fatal error: unexpectedly found nil while unwrapping an Optional value

I checked vc2NavController in the RightSegue class. It has a return type of UINavigationController?. Force unwrapping it returns nil.

As indicated in this answer (Custom Segue in Swift), I added the @objc() and ran the app. It still didn't work. The app crashes, this time giving the error:

Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Could not create a segue of class '(null)''

I don't know what to do. Please help.

Answer 1

Edit: You need to push your second viewController for it to have a navigationController. The custom segue is what causing your problem. You need to return the navigationController, or better - read this:

http://netsplit.com/custom-ios-segues-transitions-and-animations-the-right-way

If you want to stay with the custom, this may help - Custom Push Segue removes navigation bar and tab bar in story board