问在Cocos2D CCMenuItem的选择器中使用GKPeerPickerController

EN

@implementation GameOverLayer
- (id) init 
{
    self = [super init];
    if (self != nil) 
    {
        [CCMenuItemFont setFontSize:20];
        [CCMenuItemFont setFontName:@"Helvetica"];
        CCMenuItem *start = [CCMenuItemFont itemFromString:@"Play Again!" target:self selector:@selector(startGame:)];
        CCMenuItem *connect = [CCMenuItemFont itemFromString:@"Multiplayer" target:self selector:@selector(connect:)];
        CCMenu *menu = [CCMenu menuWithItems:start,connect, nil];
        [menu alignItemsVertically];
        [self addChild:menu];
    }
    return self;
}
-(void)startGame: (id)sender 
{
    [[CCDirector sharedDirector] replaceScene: [HelloWorld scene]];
}

-(void)connect: (id)sender
{
    GKPeerPickerController *peerPicker;
    peerPicker = [[GKPeerPickerController alloc] init];

    peerPicker.delegate = self;
    peerPicker.connectionTypesMask = GKPeerPickerConnectionTypeOnline | GKPeerPickerConnectionTypeNearby;

    [peerPicker show];
}
@end

".obj_class_name_GKPeerPickerController", referenced from:
Literal-Pointer@_OBJC@_cls_refs@GKPeerPickerController in GameOverScene.o
Symbol(s) not found
Collect2: id returned 1 exit status