gamekit

GameKit Integrate Game Center features into iOS 26+ games using GameKit and Swift 6.3. Provides player authentication, leaderboards, achievements, multiplayer matchmaking, access point, dashboard, challenges, and saved games. Contents Authentication Access Point Dashboard Leaderboards Achievements Real-Time Multiplayer Turn-Based Multiplayer Common Mistakes Review Checklist References Authentication All GameKit features require the local player to authenticate first. Set the authenticateHandler on GKLocalPlayer.local early in the app lifecycle. GameKit calls the handler multiple times during initialization. import GameKit func authenticatePlayer ( ) { GKLocalPlayer . local . authenticateHandler = { viewController , error in if let viewController { // Present so the player can sign in or create an account. present ( viewController , animated : true ) return } if let error { // Player could not sign in. Disable Game Center features. disableGameCenter ( ) return } // Player authenticated. Check restrictions before starting. let player = GKLocalPlayer . local if player . isUnderage { hideExplicitContent ( ) } if player . isMultiplayerGamingRestricted { disableMultiplayer ( ) } if player . isPersonalizedCommunicationRestricted { disableInGameChat ( ) } configureAccessPoint ( ) } } Guard on GKLocalPlayer.local.isAuthenticated before calling any GameKit API. For server-side identity verification, see references/gamekit-patterns.md . Access Point GKAccessPoint displays a Game Center control in a corner of the screen. When tapped, it opens the Game Center dashboard. Configure it after authentication. func configureAccessPoint ( ) { GKAccessPoint . shared . location = . topLeading GKAccessPoint . shared . showHighlights = true GKAccessPoint . shared . isActive = true } Hide the access point during gameplay and show it on menu screens: GKAccessPoint . shared . isActive = false // Hide during active gameplay GKAccessPoint . shared . isActive = true // Show on pause or menu Open the dashboard to a specific state programmatically: // Open directly to a leaderboard GKAccessPoint . shared . trigger ( leaderboardID : "com.mygame.highscores" , playerScope : . global , timeScope : . allTime ) { } // Open directly to achievements GKAccessPoint . shared . trigger ( state : . achievements ) { } Dashboard Present the Game Center dashboard using GKGameCenterViewController . The presenting object must conform to GKGameCenterControllerDelegate . final class GameViewController : UIViewController , GKGameCenterControllerDelegate { func showDashboard ( ) { let vc = GKGameCenterViewController ( state : . dashboard ) vc . gameCenterDelegate = self present ( vc , animated : true ) } func showLeaderboard ( _ leaderboardID : String ) { let vc = GKGameCenterViewController ( leaderboardID : leaderboardID , playerScope : . global , timeScope : . allTime ) vc . gameCenterDelegate = self present ( vc , animated : true ) } func gameCenterViewControllerDidFinish ( _ gameCenterViewController : GKGameCenterViewController ) { gameCenterViewController . dismiss ( animated : true ) } } Dashboard states: .dashboard , .leaderboards , .achievements , .localPlayerProfile . Leaderboards Configure leaderboards in App Store Connect before submitting scores. Supports classic (persistent) and recurring (time-limited, auto-resetting) types. Submitting Scores Submit to one or more leaderboards using the class method: func submitScore ( _ score : Int , leaderboardIDs : [ String ] ) async throws { try await GKLeaderboard . submitScore ( score , context : 0 , player : GKLocalPlayer . local , leaderboardIDs : leaderboardIDs ) } Loading Entries func loadTopScores ( leaderboardID : String , count : Int = 10 ) async throws -> ( GKLeaderboard . Entry ? , [ GKLeaderboard . Entry ] ) { let leaderboards = try await GKLeaderboard . loadLeaderboards ( IDs : [ leaderboardID ] ) guard let leaderboard = leaderboards . first else { return ( nil , [ ] ) } let ( localEntry , entries , _ ) = try await leaderboard . loadEntries ( for : . global , timeScope : . allTime , range : 1 ... count ) return ( localEntry , entries ) } GKLeaderboard.Entry provides player , rank , score , formattedScore , context , and date . For recurring leaderboard timing, leaderboard images, and leaderboard sets, see references/gamekit-patterns.md . Achievements Configure achievements in App Store Connect. Each achievement has a unique identifier, point value, and localized title/description. Reporting Progress Set percentComplete from 0.0 to 100.0. GameKit only accepts increases; setting a lower value than previously reported has no effect. func reportAchievement ( identifier : String , percentComplete : Double ) async throws { let achievement = GKAchievement ( identifier : identifier ) achievement . percentComplete = percentComplete achievement . showsCompletionBanner = true try await GKAchievement . report ( [ achievement ] ) } // Unlock an achievement completely func unlockAchievement ( _ identifier : String ) async throws { try await reportAchievement ( identifier : identifier , percentComplete : 100.0 ) } Loading Player Achievements func loadPlayerAchievements ( ) async throws -> [ GKAchievement ] { try await GKAchievement . loadAchievements ( ) ?? [ ] } If an achievement is not returned, the player has no progress on it yet. Create a new GKAchievement(identifier:) to begin reporting. Use GKAchievement.resetAchievements() to reset all progress during testing. Real-Time Multiplayer Real-time multiplayer connects players in a peer-to-peer network for simultaneous gameplay. Players exchange data directly through GKMatch . Matchmaking with GameKit UI Use GKMatchmakerViewController for the standard matchmaking interface: func presentMatchmaker ( ) { let request = GKMatchRequest ( ) request . minPlayers = 2 request . maxPlayers = 4 request . inviteMessage = "Join my game!" guard let matchmakerVC = GKMatchmakerViewController ( matchRequest : request ) else { return } matchmakerVC . matchmakerDelegate = self present ( matchmakerVC , animated : true ) } Implement GKMatchmakerViewControllerDelegate : extension GameViewController : GKMatchmakerViewControllerDelegate { func matchmakerViewController ( _ viewController : GKMatchmakerViewController , didFind match : GKMatch ) { viewController . dismiss ( animated : true ) match . delegate = self startGame ( with : match ) } func matchmakerViewControllerWasCancelled ( _ viewController : GKMatchmakerViewController ) { viewController . dismiss ( animated : true ) } func matchmakerViewController ( _ viewController : GKMatchmakerViewController , didFailWithError error : Error ) { viewController . dismiss ( animated : true ) } } Exchanging Data Send and receive game state through GKMatch and GKMatchDelegate : extension GameViewController : GKMatchDelegate { func sendAction ( _ action : GameAction , to match : GKMatch ) throws { let data = try JSONEncoder ( ) . encode ( action ) try match . sendData ( toAllPlayers : data , with : . reliable ) } func match ( _ match : GKMatch , didReceive data : Data , fromRemotePlayer player : GKPlayer ) { guard let action = try ? JSONDecoder ( ) . decode ( GameAction . self , from : data ) else { return } handleRemoteAction ( action , from : player ) } func match ( _ match : GKMatch , player : GKPlayer , didChange state : GKPlayerConnectionState ) { switch state { case . connected : checkIfReadyToStart ( match ) case . disconnected : handlePlayerDisconnected ( player ) default : break } } } Data modes: .reliable (TCP-like, ordered, guaranteed) and .unreliable (UDP-like, faster, no guarantee). Use .reliable for critical game state and .unreliable for frequent position updates. Register the local player as a listener ( GKLocalPlayer.local.register(self) ) to receive invitations through GKInviteEventListener . For programmatic matchmaking and custom match UI, see references/gamekit-patterns.md . Turn-Based Multiplayer Turn-based games store match state on Game Center servers. Players take turns asynchronously and do not need to be online simultaneously. Starting a Match let request = GKMatchRequest ( ) request . minPlayers = 2 request . maxPlayers = 4 let matchmakerVC = GKTurnBasedMatchmakerViewController ( matchRequest : request ) matchmakerVC . turnBasedMatchmakerDelegate = self present ( matchmakerVC , animated : true ) Taking Turns Encode game state into Data , end the turn, and specify the next participants: func endTurn ( match : GKTurnBasedMatch , gameState : GameState ) async throws { let data = try JSONEncoder ( ) . encode ( gameState ) // Build next participants list: remaining active players let nextParticipants = match . participants . filter { $0 . matchOutcome == . none && $0 != match . currentParticipant } try await match . endTurn ( withNextParticipants : nextParticipants , turnTimeout : GKTurnTimeoutDefault , match : data ) } Ending the Match Set outcomes for all participants, then end the match: func endMatch ( _ match : GKTurnBasedMatch , winnerIndex : Int , data : Data ) async throws { for ( index , participant ) in match . participants . enumerated ( ) { participant . matchOutcome = ( index == winnerIndex ) ? . won : . lost } try await match . endMatchInTurn ( withMatch : data ) } Listening for Turn Events Register as a listener and implement GKTurnBasedEventListener : GKLocalPlayer . local . register ( self ) extension GameViewController : GKTurnBasedEventListener { func player ( _ player : GKPlayer , receivedTurnEventFor match : GKTurnBasedMatch , didBecomeActive : Bool ) { // Load match data and update UI loadAndDisplayMatch ( match ) } func player ( _ player : GKPlayer , matchEnded match : GKTurnBasedMatch ) { showMatchResults ( match ) } } Match Data Size matchDataMaximumSize is 64 KB. Store larger state externally and keep only references in match data. Common Mistakes Not authenticating before using GameKit APIs // DON'T func submitScore ( ) { GKLeaderboard . submitScore ( 100 , context : 0 , player : GKLocalPlayer . local , leaderboardIDs : [ "scores" ] ) { _ in } } // DO func submitScore ( ) async throws { guard GKLocalPlayer . local . isAuthenticated else { return } try await GKLeaderboard . submitScore ( 100 , context : 0 , player : GKLocalPlayer . local , leaderboardIDs : [ "scores" ] ) } Setting authenticateHandler multiple times // DON'T: Set handler on every scene transition override func viewDidAppear ( _ animated : Bool ) { super . viewDidAppear ( animated ) GKLocalPlayer . local . authenticateHandler = { vc , error in / ... / } } // DO: Set the handler once, early in the app lifecycle Ignoring multiplayer restrictions // DON'T func showMultiplayerMenu ( ) { presentMatchmaker ( ) } // DO func showMultiplayerMenu ( ) { guard ! GKLocalPlayer . local . isMultiplayerGamingRestricted else { return } presentMatchmaker ( ) } Not setting match delegate immediately // DON'T: Set delegate in dismiss completion -- misses early messages func matchmakerViewController ( _ vc : GKMatchmakerViewController , didFind match : GKMatch ) { vc . dismiss ( animated : true ) { match . delegate = self } } // DO: Set delegate before dismissing func matchmakerViewController ( _ vc : GKMatchmakerViewController , didFind match : GKMatch ) { match . delegate = self vc . dismiss ( animated : true ) } Not calling finishMatchmaking for programmatic matches // DON'T let match = try await GKMatchmaker . shared ( ) . findMatch ( for : request ) startGame ( with : match ) // DO let match = try await GKMatchmaker . shared ( ) . findMatch ( for : request ) GKMatchmaker . shared ( ) . finishMatchmaking ( for : match ) startGame ( with : match ) Not disconnecting from match // DON'T func returnToMenu ( ) { showMainMenu ( ) } // DO func returnToMenu ( ) { currentMatch ? . disconnect ( ) currentMatch ? . delegate = nil currentMatch = nil showMainMenu ( ) } Review Checklist GKLocalPlayer.local.authenticateHandler set once at app launch isAuthenticated checked before any GameKit API call Player restrictions checked ( isUnderage , isMultiplayerGamingRestricted , isPersonalizedCommunicationRestricted ) Game Center capability added in Xcode signing settings Leaderboards and achievements configured in App Store Connect Access point configured and toggled appropriately during gameplay GKGameCenterControllerDelegate dismisses dashboard in gameCenterViewControllerDidFinish Match delegate set immediately when match is found finishMatchmaking(for:) called for programmatic matches; disconnect() and nil delegate on exit Turn-based match data stays under 64 KB Turn-based participants have outcomes set before endMatchInTurn Invitation listener registered with GKLocalPlayer.local.register(_:) Data mode chosen appropriately: .reliable for state, .unreliable for frequent updates NSMicrophoneUsageDescription set if using voice chat Error handling for all async GameKit calls References See references/gamekit-patterns.md for voice chat, saved games, custom match UI, leaderboard images, challenge handling, and rule-based matchmaking. GameKit documentation GKLocalPlayer GKAccessPoint GKLeaderboard GKAchievement GKMatch GKTurnBasedMatch