Game Center Leader Board Error

问题:

I created this code for game center Leaderboards, and I always get Thread 1 signal Sigabrt. The NSLOG always says this :

2014-04-15 15:27:28.441 GameCenter[38225:60b] -[GKGameCenterViewController setLeaderboardDelegate:]: unrecognized selector sent to instance 0xb48dd90
2014-04-15 15:27:28.442 GameCenter[38225:60b] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[GKGameCenterViewController setLeaderboardDelegate:]: unrecognized selector sent to instance 0xb48dd90'
*** First throw call stack:

below a screenshot of the code i have for implementing the Leaderboard:

Or/And please look at this question over here: https://stackoverflow.com/questions/23068184/game-center-leaderboard-doesnt-work-in-xcode