show Admob interstitial when with nav back button press iOS Swift

Question

i have two view controllers imageViewController and InfoViewController. i want my ad to show when the user click on back button from InfoViewController

class imageViewController: UIViewController , GADInterstitialDelegate {
    var interstitial: GADInterstitial!
 override func viewDidLoad() {

         self.interstitial = self.createAndLoadInterstitial()
         super.viewDidLoad()
}
func createAndLoadInterstitial() -> GADInterstitial {
        let interstitial: GADInterstitial = GADInterstitial(adUnitID: "ca-app-pub-3940256099942544/4411468910")
        interstitial.delegate = self
        let request = GADRequest()
        interstitial.loadRequest(request)
        print("req sent")
        return interstitial
    }
    func interstitialDidReceiveAd(ad: GADInterstitial!) {
        if (interstitial.isReady) {
            print("ad ready")
            interstitial.presentFromRootViewController(self)
        }}
     func interstitialDidDismissScreen(interstitial: GADInterstitial) {
    } 

How should i call it with back button click from infoViewController to ImageViewCroller. i also failed to solve this problem with global variable since i am new to iOS

Answer 1

I would recommend to call it in one of the UIViewController's methods. For example:

isMovingFromParentViewController()

See documentation.

EDIT:

Actually, if you want to have a VC as a delegate, you should call it from the parent VC, otherwise you will lose the delegate by popping it with the back button.

You can do it in a few ways. One would be to use a closure. Here, you would put your callback methods in the first VC and have a property in your second VC like so:

var onBack:()->()?

And you would need to set it's value when showing the second VC (for example in prepareForSegue method):

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    if let destination = segue.destinationViewController as? InfoViewController {
        destination.onBack = { ()->() in
            self.createAndLoadInterstitial()
        }
    }
}

Then, in the second view controller do this:

override func isMovingFromParentViewController() -> Bool {
    onBack?()
}

That is not tested btw:)