Show Game Centre Leaderboard not working in swift - ios

Question

I am coding in swift and I am getting the following error message from my submit button. The leaderboard does not show up in the simulator, just gives me the error message below
<GKGameCenterViewController: 0x7a8d0800> on <Chinese_Quiz.OpeningViewController: 0x78688aa0> whose view is not in the window hierarchy!
Below is all the game centre code from my app.
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
Randomize()
Hide()
authenticateLocalPlayer()
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
#IBAction func Submit(sender: AnyObject) {
saveHighscore(Score)
showLeaderboard()
}
func authenticateLocalPlayer(){
var localPlayer = GKLocalPlayer.localPlayer()
localPlayer.authenticateHandler = {(viewController, error) -> Void in
if (viewController != nil) {
self.presentViewController(viewController, animated: true, completion: nil)
}
else {
println((GKLocalPlayer.localPlayer().authenticated))
}
}
}
func gameCenterViewControllerDidFinish(gameCenterViewController: GKGameCenterViewController!)
{
gameCenterViewController.dismissViewControllerAnimated(true, completion: nil)
}
func showLeaderboard() {
var vc = self.view?.window?.rootViewController
var gc = GKGameCenterViewController()
gc.gameCenterDelegate = self
vc?.presentViewController(gc, animated: true, completion: nil)
}
func saveHighscore(score:Int) {
//check if user is signed in
if GKLocalPlayer.localPlayer().authenticated {
var scoreReporter = GKScore(leaderboardIdentifier: "ChineseWeather") //leaderboard id here
scoreReporter.value = Int64(Score) //score variable here (same as above)
var scoreArray: [GKScore] = [scoreReporter]
GKScore.reportScores(scoreArray, withCompletionHandler: {(error : NSError!) -> Void in
if error != nil {
println("error")
}
})
}
}

Answer 1

Solved by turning this:
func showLeaderboard() {
var vc = self.view?.window?.rootViewController
var gc = GKGameCenterViewController()
gc.gameCenterDelegate = self
vc?.presentViewController(gc, animated: true, completion: nil)
}
Into this:
func showLeaderboard() {
var vc = self
var gc = GKGameCenterViewController()
var gameCenterDelegate: GKGameCenterControllerDelegate!
// Above text was replaced from gc.gameCenterDelegate = self
vc.presentViewController(gc, animated: true, completion: nil)
}
I don't know why, but it worked.