description: http://twolivesleft.com/Codea/Talk/discussion/1197/objective-c-classes-for-music-play-and-interaction-with-the-game-center

aGameCenter_Codea.h

//
//  aGameCenter_Codea.h
//
//  Created by Juan Belón on 28/05/12
//  Games -> http://www.xixgames.com
//  LGPL - @juaxix - Codea connection!
//

#import <Foundation/Foundation.h>
#import <GameKit/GameKit.h>
#import <AVFoundation/AVAudioPlayer.h>

@interface aGameCenter_Codea : NSObject
    <GKLeaderboardViewControllerDelegate, AVAudioPlayerDelegate> 
{
    bool hasGameCenter;
    bool playing;
    AVAudioPlayer *player;
}

- (void) start;
- (void) authenticateLocalPlayer;
- (void) registerForAuthenticationNotification;
- (void) authenticationChanged;
- (BOOL) isGameCenterAvailable;
- (void) leaderboardViewControllerDidFinish:
         (GKLeaderboardViewController *)viewController;
- (void) showLeaderboard;
- (void) reportScore:(int) score;
- (void) playMusic:(int) songNumber;
- (void) stopMusic;
@end

aGameCenter_Codea.m

//
//  aGameCenter_Codea.m
//
//  Created by Juan Belón on 28/05/12
//  Games -> http://www.xixgames.com
//  LGPL - @juaxix - Codea connection!
//

#import "aGameCenter_Codea.h"
#import "SharedRenderer.h"

@implementation aGameCenter_Codea

- (id)init
{
    self = [super init];
    player = [[AVAudioPlayer alloc] init];
    playing= false;
    return self;
}

- (void)dealloc
{
    [player release];
    [super dealloc];
}

- (void) start {
    //Game Center
    hasGameCenter = false;
    
    [self authenticateLocalPlayer];
}


- (BOOL) isGameCenterAvailable
{
    // Check for presence of GKLocalPlayer API.   
    Class gcClass = (NSClassFromString(@"GKLocalPlayer"));   
    
    // The device must be running running iOS 4.1 or later.   
    NSString *reqSysVer = @"4.1";   
    NSString *currSysVer = [[UIDevice currentDevice] systemVersion];   
    BOOL osVersionSupported = ([currSysVer compare:reqSysVer options:NSNumericSearch] != NSOrderedAscending);   
    
    return (gcClass && osVersionSupported);
}

- (void)authenticateLocalPlayer {
    
    if(![self isGameCenterAvailable]){
        hasGameCenter = false;
        return;
    }
    [[GKLocalPlayer localPlayer] authenticateWithCompletionHandler:^(NSError *error) {      
        if (error == nil){
            [self registerForAuthenticationNotification];
            hasGameCenter = true;
        }else{
            hasGameCenter = false;
        }
    }];
}

- (void)registerForAuthenticationNotification
{
    NSNotificationCenter *nc = [NSNotificationCenter defaultCenter];
    [nc addObserver: self selector:@selector(authenticationChanged) name:GKPlayerAuthenticationDidChangeNotificationName object:nil];
}

- (void)authenticationChanged
{
    if([self isGameCenterAvailable ]){
        return;
    }
    
    if ([GKLocalPlayer localPlayer].isAuthenticated){      
        hasGameCenter = true;
    }else{
        hasGameCenter = false;
    }
}
- (void)showLeaderboard
{
    GKLeaderboardViewController *leaderBoardCont = [[GKLeaderboardViewController alloc] init];
    if (leaderBoardCont) {
        leaderBoardCont.category=@"YOUR_SCORE_BOARD_UNIQUE_NAME_FROM_ITUNES_CONNECT";
        leaderBoardCont.timeScope=GKLeaderboardTimeScopeToday;
        leaderBoardCont.leaderboardDelegate=self;
        
        [[SharedRenderer renderer] presentModalViewController:leaderBoardCont animated:YES];
    }
}

- (void)leaderboardViewControllerDidFinish:(GKLeaderboardViewController *)viewController
{
    [[SharedRenderer renderer] dismissModalViewControllerAnimated:YES];
}

- (void) reportScore:(int) score
{
    GKScore *scoreReporter = [[[GKScore alloc] initWithCategory:
          @"YOUR_SCORE_BOARD_UNIQUE_NAME_FROM_ITUNES_CONNECT"] autorelease];
    if(scoreReporter){
        scoreReporter.value = score;
        
        [scoreReporter reportScoreWithCompletionHandler:^(NSError *error) {   
            if (error != nil){
                // handle the reporting error
                
            }
        }];   
    }
}

- (void) playMusic:(int) songNumber {
    NSString* resourcePath = [[NSBundle mainBundle] resourcePath];
    NSString* song = [[NSString alloc] initWithString:@""];
    NSError* err;
    
    switch (songNumber) {
        case 1: //menu song
            song = @"/menu.MP3";
            break;
        case 2:
            song = @"/game.MP3";
            break;
        case 3:
            song = @"/winner.MP3";
        default:
            break;
    }

    if ([song isEqualToString:@""]){
        return ;
    }
    //NSLog(@"Playing song %d: %@",songNumber,song);
    resourcePath = [resourcePath stringByAppendingString:song];
    //NSLog(@"Path to play: %@", resourcePath);
    //Initialize our player pointing to the path to our resource
    if (playing && player) {
        [player stop];
        playing = false;
    }
    player = [[AVAudioPlayer alloc] initWithContentsOfURL:
              [NSURL fileURLWithPath:resourcePath] error:&err];
    

    if( err ){
        //bail!
        NSLog(@"Failed with reason: %@", [err localizedDescription]);
    }
    else{
        //set our delegate and begin playback
        player.delegate = self;
        [player prepareToPlay];
        player.numberOfLoops = -1; //One Infinite Loop (music!) ;)
        [player play];
        playing = true;
    }

}

- (void) stopMusic {
    if (playing){
        [player stop];
        playing = false;
    }
}
@end