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](#authentication)
- [Access Point](#access-point)
- [Dashboard](#dashboard)
- [Leaderboards](#leaderboards)
- [Achievements](#achievements)
- [Real-Time Multiplayer](#real-time-multiplayer)
- [Turn-Based Multiplayer](#turn-based-multiplayer)
- [Common Mistakes](#common-mistakes)
- [Review Checklist](#review-checklist)
- [References](#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.

```swift
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](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.

```swift
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:

```swift
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:

```swift
// 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`.

```swift
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: GKGameCenterVie