interstitialWillDismissScreen only being called once

Question

I am using Admob interstitials in my swift project and I am having trouble reloading the ads. The first interstitial displays fine, and when interstitialWillDismissScreen is called, it exits back to the game and reloads a new interstitial as it's supposed to. However, neither interstitialDidReceiveAd nor interstitialWillDismissScreen are called again, so after the second ad is displayed, no other ads come through. What am I missing?

import GoogleMobileAds

let appDelegate = (UIApplication.sharedApplication().delegate as! AppDelegate)

class GameScene: SKScene, GKGameCenterControllerDelegate, GADInterstitialDelegate {

    var interstitial: GADInterstitial!

    override func didMoveToView(view: SKView) {

        //preload interstitial ad
        if NSUserDefaults.standardUserDefaults().boolForKey("paidToRemoveAds") == false {
            interstitial = loadAd()
        }

        interstitial.delegate = self
    }

    func gameOver() {
        runGoogleAd()
    }

    func loadAd() -> GADInterstitial {
        let ad = GADInterstitial(adUnitID: "ca-app-pub-2963481692578498/7292484569")
        let request = GADRequest()
        request.testDevices = [kGADSimulatorID]
        ad.loadRequest(request)
        return ad
    }

    func runGoogleAd() {
        if interstitial.isReady {
            interstitial.presentFromRootViewController((appDelegate.window?.rootViewController)!)
        }
    }

    func interstitialDidReceiveAd(ad: GADInterstitial!) {
        print("ad loaded")
    }

    func interstitialWillDismissScreen(ad: GADInterstitial!) {
        interstitial = loadAd()
        print("loading new ad")
    }
}

Answer 1

I assume loadAd() creates a new instance? You need to set the delegate on the new instance:

func interstitialWillDismissScreen(ad: GADInterstitial!) {
    interstitial = loadAd()

    interstitial.delegate = self  // <-- You forgot this.

    print("loading new ad")
}

Actually you should probably set the delegate in loadAd() since it is an instance member of this class.