unified_game_services_game_center 0.1.0

Apple Game Center provider for unified_game_services, backed by GameKit via pure-Dart Objective-C FFI (package:objective_c). macOS/iOS only.

unified_game_services_game_center

Apple Game Center provider for unified_game_services, backed by GameKit through pure-Dart Objective-C FFI (package:objective_c). No Flutter dependency — the same code runs in a Flutter app, a custom Dart game engine, a CLI, or a server, as long as it runs on macOS or iOS.

Supported capabilities

Capability	Supported	Notes
Authentication	✅	GKLocalPlayer
Achievements	✅	GKAchievement (+ GKAchievementDescription); progress is a 0–100 % mapped onto steps-out-of-100
Leaderboards	✅	GKLeaderboard (submit + entries, time-scope and friends/global collections)
Stats	❌	GameKit has no portable numeric-stat concept
Cloud save	⏸️	GKSavedGame — planned
Friends	⏸️	loadFriends — planned
Rich presence	❌	no GameKit equivalent

Runtime requirements (host-supplied)

GameKit talks to the OS Game Center service, and the OS — not this package — imposes two requirements the host process must meet:

1. A signed app bundle. The executable must run inside a code-signed .app/.ipa whose bundle id is registered in App Store Connect, with the matching entitlements/provisioning. A bare dart run has no bundle, so GameKit refuses to authenticate (GKErrorNotAuthenticated). A Flutter macOS/iOS app already is such a bundle; a custom engine must package itself as one.
2. A pumped main run loop. GameKit delivers completion handlers on the main dispatch queue / CFRunLoop. The host must keep that run loop running for the returned Futures to complete. Flutter/AppKit apps do this already; a headless engine must pump CFRunLoopRun() on the main thread.

This mirrors how the Steam provider needs the Steam client running: the capability is pure Dart, but the surrounding environment is the host's job.

Usage

import 'package:unified_game_services/unified_game_services.dart';
import 'package:unified_game_services_game_center/unified_game_services_game_center.dart';

final services = UnifiedGameServices(providers: [
  GameCenterProvider(
    leaderboardIds: {'global': 'com.example.game.highscores'},
    achievementIds: {'first_win': 'com.example.game.firstwin'},
  ),
]);

final player = await services.signIn();
await services.unlockAchievement('first_win');
await services.submitScore(leaderboardId: 'global', score: 4200);
final board = await services.getLeaderboard('global', maxResults: 10);

(Or register globally with GameCenterProvider.registerWith(...) and construct UnifiedGameServices() with no arguments — both styles work with every provider.)

See example/ for a complete sample.

GameKit bindings

The committed lib/src/gamekit_bindings.dart is generated from the macOS SDK GameKit headers with ffigen (see ffigen_gamekit.yaml). It is committed so consumers don't need Xcode. To regenerate (macOS + Xcode required):

./tool/regenerate_bindings.sh

The committed lib/src/gamekit_bindings.dart.m holds the ffigen-generated Objective-C block trampolines. The package's build hook (hook/build.dart) compiles it into a dynamic library at consumer build time — so a consuming app needs the Apple toolchain (clang via Xcode Command Line Tools) and a native-assets-capable build (Flutter macOS/iOS, or dart/dart test on Dart 3.12+). No Apple SDK is shipped: the .m is our generated glue, and GameKit itself is dlopen'd from the OS at runtime.

License

MIT — see the LICENSE file.

This is an independent, unofficial library, not affiliated with or endorsed by any platform vendor. Third-party credits, trademark notices, and the Steamworks SDK redistribution terms are in the repository's NOTICE.md.