App crashing when not logged into Game Center

Question

Currently, my app prompts a user to log into Game Center as soon as they open the app. Once logged in, they can view their achievements and leaderboards. However; if the user declines to log into game center and then presses the leaderboard or achievement button, the entire app crashes. What the app should do in this situation is re-prompt the user to log in. Any suggestions would be greatly appreciated.

class viewController: UIViewController, GKGameCenterControllerDelegate {

    var highscore = NSUserDefaults.standardUserDefaults().integerForKey("highscore")
    var loggedin = 1

    override func viewDidLoad() {
        super.viewDidLoad()
        login()
    }

    func login() {
        println("Game Center Login Called")
        let localPlayer = GKLocalPlayer.localPlayer()
        loggedin = 2

        // Handle the authentication
        localPlayer.authenticateHandler = {(Home: UIViewController!, error: NSError!) -> Void in
            if Home != nil {
                println("Authentication is being processed.")
                self.presentViewController(Home, animated: true, completion: nil)

            } else {
                println("Player has been successfully authenticated.")
            }
        }
    }

    func showLeaderboard() {
        let gkScore = GKScore(leaderboardIdentifier: "high_Score_Leader_Board")
        gkScore.value = Int64(highscore)
        GKScore.reportScores([gkScore], withCompletionHandler: ( { (error: NSError!) -> Void in
            if (error != nil) {
                // handle error
                println("Error: " + error.localizedDescription);
            } else {
                println("Score reported: \(gkScore.value)")
            }
        }))

        var gcViewController: GKGameCenterViewController = GKGameCenterViewController()
        gcViewController.gameCenterDelegate = self

        gcViewController.viewState = GKGameCenterViewControllerState.Leaderboards

        gcViewController.leaderboardIdentifier = "high_Score_Leader_Board"
        self.showViewController(gcViewController, sender: self)
        self.presentViewController(gcViewController, animated: true, completion: nil)
    }

    @IBAction func gameCenterButtoPressed(sender: AnyObject) {
        if loggedin == 2 {
            showLeaderboard()

        }

        else {
            login()
        }
    }

    @IBAction func pointButtonScored(sender: AnyObject) {
       ReportAchievment("testbutton", percentComplete: 100)
    }

    func gameCenterViewControllerDidFinish(gcViewController: GKGameCenterViewController!)
    {
        self.dismissViewControllerAnimated(true, completion: nil)
    }

    func showAchievements() {
        var gcViewController: GKGameCenterViewController = GKGameCenterViewController()
        gcViewController.gameCenterDelegate = self

        gcViewController.viewState = GKGameCenterViewControllerState.Achievements

        self.showViewController(gcViewController, sender: self)
        self.presentViewController(gcViewController, animated: true, completion: nil)
    }

    func ReportAchievment(identifier : String, percentComplete : Double)
    {
        var achievement = GKAchievement(identifier: identifier)

        if(achievement != nil)
        {
            achievement.percentComplete = percentComplete;
            achievement.showsCompletionBanner = true

            GKAchievement.reportAchievements([achievement], withCompletionHandler: { (error : NSError!) -> Void in
                println("Achievement reported")
            })
        }
    }

    @IBAction func achievementButtonPressed(sender: AnyObject) {

       showAchievements()
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
}

Zachary Espiritu Zachary Espiritu · Accepted Answer · 2015-08-10T16:45:15

This is the code that I use to authenticate the player for Game Center. You can call the checkIfPlayerIsLoggedIn() function the moment your game loads, which will check to see if the player is already logged in. If they player isn't, it will move to the loginPlayer() function, which attempts to log the player in if Game Center has already been setup, and if not, it will display the Game Center login screen. If the player chooses not to log in, it will return an error, which from there you can decide how to handle it (which in your case would probably be telling the user that they have to sign in and attempting to display the view controller again)

let localPlayer = GKLocalPlayer.localPlayer()
var delegate: GameCenterInteractorNotifications?
var callingViewController: UIViewController?

func checkIfPlayerIsLoggedIn()
{
    if (self.localPlayer.authenticated == false)
    {
        self.loginPlayer()
    } else
    {
        self.localPlayer.registerListener(self)
        // Do achievement loading and matchmaking handling here
    }
}

private func loginPlayer()
{
    self.delegate?.willSignIn()

    self.localPlayer.authenticateHandler = {(viewController : UIViewController!, error : NSError!) -> Void in

        if (viewController != nil)
        {
            dispatch_async(dispatch_get_main_queue(), {
                self.presentViewController(viewController, animated: true, completion: nil)
            })
        }

        else if (self.localPlayer.authenticated == true) // Player signed in
        {
            self.localPlayer.registerListener(self)
            self.delegate?.didSignIn()
        }

        else // Player did not sign in
        {
            self.delegate?.failedToSignIn()
        }

        if (error != nil)
        {
            println("Failed to sign in with error:\(error.localizedDescription).")
            self.delegate?.failedToSignInWithError(error)
            // Add code to determine what to do with the error
        }
    }
}

App crashing when not logged into Game Center

2 Answers