static void InterstitialDidCompleteCallback(IntPtr interstitialClient)
        {
            InterstitialClient client = IntPtrToInterstitialClient(interstitialClient);

            if (client.OnAdVideoFinished != null)
            {
                client.OnAdVideoFinished(client, EventArgs.Empty);
            }
        }
        static void InterstitialVideoDidCloseCallback(IntPtr interstitialClient)
        {
            InterstitialClient client = IntPtrToInterstitialClient(interstitialClient);

            if (client.OnAdClosed != null)
            {
                client.OnAdClosed(client, EventArgs.Empty);
            }
        }
        static void InterstitialDidReceivedAdCallback(IntPtr interstitialClient)
        {
            InterstitialClient client = IntPtrToInterstitialClient(interstitialClient);

            if (client.OnAdLoaded != null)
            {
                client.OnAdLoaded(client, EventArgs.Empty);
            }
        }
        static void InterstitialDidFailToReceiveAdWithErrorCallback(IntPtr interstitialClient, string error)
        {
            InterstitialClient client = IntPtrToInterstitialClient(interstitialClient);

            if (client.OnAdFailedToLoad != null)
            {
                AdFailedEventArgs args = new AdFailedEventArgs()
                {
                    Message = error
                };
                client.OnAdFailedToLoad(client, args);
            }
        }