How to Put Gamecenter on Application with Swift

Game Center - sending and receiving data with Swift

A quick and dirty solution would be something like this:

func encodeGamePacket(packet: GamePacket) -> NSData {
    return NSData(bytes: &gamePacket, length: MemoryLayout<GamePacket>.size)
}

func decodeGamePacket(data: NSData) -> GamePacket? {
    var tempBuffer:GamePacket? = nil
    data.getBytes(&tempBuffer, length: MemoryLayout<GamePacket>.size)
    return tempBuffer
}

I have not messed with direct addresses myself under swift yet, so I am not entirely sure whether this is the best approach. Note that I used an optional return type, you can design this differently in your code (maybe add some checks, unwrap the variable and return it or throw an exception when the checks fail).

Alternatively you could design a method that writes your GamePacket into a String (for readability, for example), which you can in turn transform into NSData (String has a data method) or you turn GamePacket into an NSCoding compliant class that offers methods to convert itself into NSData as well.

Swift - Game Center not available

Assuming that you've enabled Game Center in your app and also added a leaderboard in iTunes Connect then you need to authenticate your player before you can show GC. Also, be sure that you've created a test user in iTunes Connect that you can use to log in to Game Center when the prompt appears.

Your MenuViewController should authenticate the local player in viewDidLoad like so:

class MenuViewController: UIViewController,
            GKGameCenterControllerDelegate
{
    var leaderboardIdentifier: String? = nil
    var gameCenterEnabled: Bool = false

    override func viewDidLoad()
    {
        super.viewDidLoad()

        //Your code that sets up your scene or other set up code

        //HERE IS WHERE YOU AUTHENTICATE
        authenticateLocalPlayer()
    }

    func authenticateLocalPlayer()
    {
        var localPlayer = getLocalPlayer() // see GKLocalPlayerHack.h
        localPlayer.authenticateHandler =
            { (viewController : UIViewController!, error : NSError!) -> Void in
                if viewController != nil
                {
                    self.presentViewController(viewController, animated:true, completion: nil)
                }
                else
                {
                    if localPlayer.authenticated
                    {
                        self.gameCenterEnabled = true
                        localPlayer.loadDefaultLeaderboardIdentifierWithCompletionHandler
                        { (leaderboardIdentifier, error) -> Void in
                            if error != nil
                            {
                                print("error")
                            }
                            else
                            {
                                self.leaderboardIdentifier = leaderboardIdentifier
                                print("\(self.leaderboardIdentifier)") //in your example "VHS" should be returned
                            }
                        }
                    }
                    else
                    {
                        print("not able to authenticate fail")
                        self.gameCenterEnabled = false

                        if error
                        {
                            print("\(error.description)")
                        }
                        else
                        {
                            print(    "error is nil")
                        }
                    }
                }
        }
    }

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

After you've successfully authenticated then you should be able to present Game Center.

Note the line:
var localPlayer = getLocalPlayer() // see GKLocalPlayerHack.h

To get that to work you need to do a little hack to get GKLocalPlayer to instantiate correctly in Swift.

Create a new class in Objective-C and name the file GKLocalPlayerHack.h/m

In the header put:

//  GKLocalPlayerHack.h
// Issue with GameKit and Swift
// https://stackoverflow.com/questions/24045244/game-center-not-authenticating-using-swift

#import <GameKit/GameKit.h>

@interface GKLocalPlayerHack : NSObject

GKLocalPlayer *getLocalPlayer(void);

@end

In the implementation file put:

// GKLocalPlayerHack.m
// Issue with GameKit and Swift
// https://stackoverflow.com/questions/24045244/game-center-not-authenticating-using-swift

#import "GKLocalPlayerHack.h"

@implementation GKLocalPlayerHack

GKLocalPlayer *getLocalPlayer(void)
{
    return [GKLocalPlayer localPlayer];
}

@end

Be sure to add:

#import "GKLocalPlayerHack.h"

To your bridging header.
Credit to @marmph for his answer in this question: Game Center not authenticating using Swift

Unable to Enable Game Center for my App

1. Enable Game Center in your App ID. To do this, log into developer.apple.com and go to Member Center -> Certificates,Ids & Devices -> App Ids and select your App id. Then make sure Game Center is enabled
2. Make sure Game Center is enabled in Xcode. You can check by going to Project -> Capabilities -> and the check that Game Center is turned on. Once you do that follow to step 3. If it isn't enable it and press fix issues and Xcode should resolve everything by itself.
3. Go to iTunes Connect -> My Apps -> Select your app. Under the upper left corner next to App Store you should see Features.
   
   
   Select it, and you'll be taken to this page:
   
   Press on Game Center and voila, you're ready to set up Leaderboards and Achievements. Congrats.
   

EDIT:

What appears to have been the problem was the use of production certificates while development, as the OP pointed out that the PN error got fixed in the released build. Another way to try to fix that type of error is to check if the correct and new provisioning profile is installed.

Hope that helps, Julian!

Application is not recognized by Game Center after building with Xcode 6.0.1

Alright I'm able to figure out why. Forgot to mention that I upgraded my test iOS device to 8.0 as well.

It turns out that you need to go to Settings>Game Center and manually enable Sandbox.

I got it working now. Hopefully this helps anyone who face this issue.

why do i not have 'gamecenter' option in my list of capabilities

https://developer.apple.com/documentation/xcode/adding-capabilities-to-your-app
Some capabilities such as 'gamecenter' requires extra configurations first to your app such as paying the yearly fee to be on apple developer program before being allowed to access them.

Game Center not authenticating using Swift

This issue has been resolved by Apple - just call:

GKLocalPlayer.localPlayer()

Previously, the issue was that GKLocalPlayer() does not return the GKLocalPlayer singleton, but instead returns a new GKLocalPlayer instance.

If you were on the Xcode 6 BETA, you could add a C function or Objective-C method that returns the real GKLocalPlayer singleton, then use this in Swift. This is the gist of my workaround (with bad naming conventions):

In an Objective-C header:

GKLocalPlayer *getLocalPlayer(void);

In an Objective-C implementation:

GKLocalPlayer *getLocalPlayer(void) {
    return [GKLocalPlayer localPlayer];
}

In your bridging header:

#import "ThatHeader.h"

Then whenever you need to access the GKLocalPlayer singleton in Swift, you can just use getLocalPlayer() instead of GKLocalPlayer(). It's probably a better idea to stick that in an method of a GKLocalPlayer category.

However, this is no longer necessary as detailed above.

GameCenter reporting achievements Swift 3

It would appear that it can take a long time for Apple to set up Game Center achievements, and in the end the code was Ok. Go figure.

Swift Game Center Authentication

This question has to do with a bug in GKLocalPlayer() and Swift. Please see this very detailed answer that I gave from a few weeks ago:

Swift - Game Center not available

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