我想在game center中上传分数进行排名，我复制了网上的例子http://my.oschina.net/u/1582495/blog/264418，可是编译没错，运行中出错
错误如下，请问说怎么回事，应该如何解决
Undefined symbols for architecture arm64:
“OBJC_CLASS_GKScore", referenced from:
objc-class-ref in GameKitHelper.o
"_OBJC_CLASS__GKLeaderboardViewController”, referenced from:
objc-class-ref in GameKitHelper.o
“OBJC_CLASS$_GKLocalPlayer”, referenced from:
objc-class-ref in GameKitHelper.o
“_GKPlayerAuthenticationDidChangeNotificationName”, referenced from:
- in GameKitHelper.o
ld: symbol(s) not found for architecture arm64
clang: error: linker command failed with exit code 1 (use -v to see invocation)