Apple の Game Center スコア値を取得する

import SwiftUI
import GameKit

@main
struct GameCenterGetScoreTestApp: App {
    @UIApplicationDelegateAdaptor(AppDelegate.self) var delegate

    var body: some Scene {
        WindowGroup {
            GameCenterGetScoreView()
        }
    }
}

class AppDelegate: UIResponder, UIApplicationDelegate {

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        // Show GameCenter AccessPoint
        GKAccessPoint.shared.location = .topLeading
        GKAccessPoint.shared.showHighlights = true
        GKAccessPoint.shared.isActive = true

        // Call GameCenter authentication
        let window = UIWindow(frame: UIScreen.main.bounds)
        window.rootViewController = UIViewController()
        if let _ = window.rootViewController {
            print("GameCenterのログイン処理を呼び出します")
            GameCenterHelper.loginGameCenter()
        }
        return true
    }
}

import GameKit

struct GameCenterHelper {

    static func loginGameCenter() {
        GKLocalPlayer.local.authenticateHandler = { _, error in
            if error != nil {
                print("You are not logged into GameCenter.")
                print(error.debugDescription)
            } else if GKLocalPlayer.local.isAuthenticated {
                print("You are logged into GameCenter.")
            }
        }
    }
}

import SwiftUI

struct GameCenterGetScoreView: View {

    @ObservedObject private var viewModel = GameCenterGetScoreViewModel()

    var body: some View {
        VStack {
            Spacer()
            VStack {
                Button {
                    viewModel.loadScore()
                } label: {
                    Text("Load Score")
                }
                .buttonStyle(.borderedProminent)
                Text("Load latest scores if you are logged into GameCenter.").font(.caption)
            }.padding()

            Text("WorldScore : \(viewModel.worldHighScore)")
            Text("myScore : \(viewModel.yourHighScore)")
            Spacer()
        }
    }
}

import GameKit

class GameCenterGetScoreViewModel: ObservableObject {

    // World score
    @Published private(set) var worldHighScore = 0
    // Your score
    @Published private(set) var yourHighScore = 0

    func loadScore() {
        print("load scores from Loaderboarder.")
        if GKLocalPlayer.local.isAuthenticated {
            print("You are logged in. Start to load scores from Game Center.")
            // Get the Leaderboard ID of this app that you have previously registered in App Store Connect
            // (only one ID is registered here).
            GKLocalPlayer.local.loadDefaultLeaderboardIdentifier(
                completionHandler: { (leaderboardIdentifer, error) in
                if error != nil { // Error occured
                    print(error!.localizedDescription)
                } else { // Got the loaderBoarderIdentifier for this app.
                    // Load scores
                    if let leaderboarderId = leaderboardIdentifer {
                        print("Default leaderboardIdentifer is \(leaderboarderId).")
                        // ここに、下記の スコア取得コード を記述する
                    }
                }
            })
        } else {
            // If you are not logged into GameCenter, displayed scores is set to zero.
            self.worldHighScore = 0
            self.yourHighScore = 0
        }
    }

}

GKLeaderboard.loadLeaderboards(IDs: [leaderboarderId]) { (boards, _) in
    boards?.first?.loadEntries(
        for: .global, 
        timeScope: .allTime, 
        range: NSRange(location: 1, length: 1), 
        completionHandler: { (local, entries, _, _) in
            // If entries are loaded, set the value to worldHighScore
            if let entries = entries {
                self.worldHighScore = entries[0].score
            }
            // If local is loaded, set the value to yourHighScore
            if let local = local {
                self.yourHighScore = local.score
            }
        }
    )
}