// Creates an RewardVideo.
 public void CreateRewardVideoAd()
 {
     this.rewardVideoClientPtr = (IntPtr)GCHandle.Alloc(this);
     this.RewardVideoPtr       = YumiExterns.CreateYumiRewardVideo(this.rewardVideoClientPtr);
     // call back
     YumiExterns.SetRewardVideoCallbacks(
         this.RewardVideoPtr,
         RewardVideoDidOpenAdCallback,
         RewardVideoDidStartPlayingCallback,
         RewardVideoDidRewardCallback,
         RewardVideoDidCloseCallback
         );
 }