How do I show the GameCenter's leaderboard from another UIViewController

Question

I have two UIViewControllers, MainViewController and HighScoreViewController.

In the MainViewController (the initial view controller that the user sees upon using the app) I have all the methods to log into Game Center and save the high score to a leaderboard.

override func viewDidLoad() {
    super.viewDidLoad()

    authenticateLocalPlayer()
    if totalHighScore > prevTotalHighScore {
        saveHighScore("totalHighScore", score: totalHighScore)
        prevTotalHighScore = totalHighScore
        NSUserDefaults.standardUserDefaults().setObject(prevTotalHighScore, forKey: "prevtotalhighscore")
    }
}

func authenticateLocalPlayer() {
    let localPlayer: GKLocalPlayer = GKLocalPlayer.localPlayer()

    localPlayer.authenticateHandler = {(ViewController, error) -> Void in
        if((ViewController) != nil) {
            // 1 Show login if player is not logged in
            self.presentViewController(ViewController!, animated: true, completion: nil)
        }
        else {
            print("Authentication is \(GKLocalPlayer.localPlayer().authenticated)")
        }
    }

}

func gameCenterViewControllerDidFinish(gameCenterViewController: GKGameCenterViewController) {
    gameCenterViewController.dismissViewControllerAnimated(true, completion: nil)
}

func saveHighScore(identifier: String, score: Int) {

    if GKLocalPlayer.localPlayer().authenticated {
        let scoreReport = GKScore(leaderboardIdentifier: identifier)

        scoreReport.value = Int64(score)

        let scoreArray: [GKScore] = [scoreReport]

        GKScore.reportScores(scoreArray, withCompletionHandler: { (error) -> Void in

            if error != nil {
                print(error)
            }
            else {
                print("Posted score of \(score)")
            }
        })
    }
}

First of all, is this the best way to implement as such?

Secondly, my HighScoreViewController has a button that says 'LEADERBOARD' where if the user taps on, Game Center leaderboard for my game would pop up. How do I go about implementing said button? I already have a button set up and and @IBAction method linked to it, but I have no idea what code to place in it since all of the main Game Center code is placed inside the MainViewController.

Answer 1

Once you're authenticated with Game Center, it doesn't matter which controller retrieves the leaderboard. You say you already have a method linked to your button. So, you'll just add the retrieval code there. Apple's GKLeaderBoard reference has an example in obj-c for downloading leaderboard data:

GKLeaderboard *leaderboardRequest = [[GKLeaderboard alloc] init];
if (leaderboardRequest != nil)
{
    leaderboardRequest.playerScope = GKLeaderboardPlayerScopeGlobal;
    leaderboardRequest.timeScope = GKLeaderboardTimeScopeToday;
    leaderboardRequest.identifier = @" ~~ your leaderboard identifier goes here ~~ "
    leaderboardRequest.range = NSMakeRange(1,10);
    [leaderboardRequest loadScoresWithCompletionHandler: ^(NSArray *scores, NSError *error) 
    {
        if (error != nil)
        {
            // Handle the error.
        }
        if (scores != nil)
        {
            // Process the score information.
        }
    }];
}