#pragma mark -单例方法static GameKitHelper *sharedInstance;+ (id)allocWithZone:(struct _NSZone *)zone{    static dispatch_once_t onceToken;    dispatch_once(&onceToken, ^{        sharedInstance = [super allocWithZone:zone];    });    return sharedInstance;}+ (GameKitHelper *)sharedGameKitHelper{    static dispatch_once_t onceToken;    dispatch_once(&onceToken, ^{        sharedInstance = [[GameKitHelper alloc] init];    });    return sharedInstance;}