Displaying Game Centre Leaders board from Swift

In last post, I showed how we can authenticate local player and how we can post score to default leader board.

In this post, I will show how we can display leader board using swift gamekit API. Below code shows how we can display GKGameCenterViewController. Game center viewcontroller needs delegate, which is called when view is dismissed. Also we need parent viewcontroller which will be used to display GKGameCenterViewController.

func showLeaderboard(viewController: UIViewController, 
    gameCenterDelegate: GKGameCenterControllerDelegate) {
    let gameCenterVC: GKGameCenterViewController = GKGameCenterViewController();
    gameCenterVC.leaderboardIdentifier = defaultLeaderBoard;
    gameCenterVC.gameCenterDelegate = gameCenterDelegate;
    viewController.presentViewController(gameCenterVC, animated: true, completion: nil);
}

Now we have code that can display leader board, but we need to make our class conform to GKGameCenterControllerDelegate protocol and implement required method. Below is code for delegate method. Which simply dismiss presented view controller.

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

So, as you can see it's quite simple. Hope this will be helpful.

Posting score to Game Kit Leader board using swift

As you might already know, I recently started exploring Swift language and now I am trying out GameKit framework. While I have some experience in working with GameKit using Objective C. I wanted to do the same thing using swift. As such there are no API changes while using GameKit with Swift or Objective C. However there are some syntax change.

In this post, I will show how to Authenticate local player using GameKit framework and post score to LeaderBoard defined in iTune Connect Application setting.

Following is code snippet that shows how to Authenticate Local player. This function takes ViewController as argument. Login dialog will be displayed using this View controller. Rest will be taken care by GameKit framework.

func authenticateLocalPlayer(viewController: UIViewController) {
    let localPlayer: GKLocalPlayer = GKLocalPlayer.localPlayer()
    
    localPlayer.authenticateHandler = {(ViewController, error) -> Void in
        if((ViewController) != nil) {
            // 1 Show login if player is not logged in
            viewController.presentViewController(ViewController, animated: true, completion: nil)
        } else if (localPlayer.authenticated) {
            // 2 Player is already euthenticated & logged in, load game center
            self.isGameCenterEnabld = true                
        } else {
            // 3 Game center is not enabled on the users device
            self.isGameCenterEnabld = false
            println("Local player could not be authenticated, disabling game center")
            println(error)
        }
        
    }
    
}

Now we have authenticated local player. So when we are ready to post score to Leader Board. We can use below function. Here we are posting score to "defaultLeaderBoard". Which is identifier of Leader board defined in iTune connect App setting.

func submitScore( score: Int) {
    if( !isGameCenterEnabld ) {
        return;
    }
    
    var sScore = GKScore(leaderboardIdentifier: defaultLeaderBoard)
    sScore.value = Int64(score)
    
    let localPlayer: GKLocalPlayer = GKLocalPlayer.localPlayer()
    
    GKScore.reportScores([sScore], withCompletionHandler: { (error: NSError!) -> Void in
        if error != nil {
            println(error.localizedDescription)
        } else {
            println("Score submitted")
            
        }
    })
}

That's it. Hope this will be useful.

Matching custom NSObject with isEqual and hash

While working on one multiplayer game for iOS using GameKit, I faced issue while comparing object.

For single player version I was not facing this issue but while running multiplayer version I was facing this issue. After debugging a little I realised condition for comparing object's value is failing and it turned out that I was comparing object's address rather then its value. As for Multiplayer game I was creating object using data from server/host, I needed to compare object's value and not its address.

For objectiveC, if you want to compare object's value using "==" operator, you need to overload isEqual and hash method as shown like below.

-(BOOL)isEqual:(id) other {
    if (other == self)
        return YES;
    
    if (!other || ![other isKindOfClass:[self class]])
        return NO;
    
    Card* otherCard = other;
    return ( mSuit == otherCard.mSuit && mRank == otherCard.mRank);
}

- (NSUInteger)hash {
    NSUInteger hash = 0;
    hash += [[NSNumber numberWithInt:mSuit] hash];
    hash += [[NSNumber numberWithInt:mRank] hash];
    return hash;
}

Note that you need to overload both method together, overloading only one will not work. Once I overloaded above method my multiplayer version started working as normal.