private static void windowAdDidFailToShowCallback(IntPtr windowAdClient)
        {
            WindowAdClient client = IntPtrToWindowAdClient(windowAdClient);

            if (client.OnAdFailToShow != null)
            {
                client.OnAdFailToShow(client, EventArgs.Empty);
            }
        }
        private static void windowAdDidCompleteCallback(IntPtr windowAdClient)
        {
            WindowAdClient client = IntPtrToWindowAdClient(windowAdClient);

            if (client.OnAdFinished != null)
            {
                client.OnAdFinished(client, EventArgs.Empty);
            }
        }
        private static void windowAdDidStartPlayingCallback(IntPtr windowAdClient)
        {
            WindowAdClient client = IntPtrToWindowAdClient(windowAdClient);

            if (client.OnAdStarted != null)
            {
                client.OnAdStarted(client, EventArgs.Empty);
            }
        }
        private static void windowAdDidReceivedAdCallback(IntPtr windowAdClient)
        {
            WindowAdClient client = IntPtrToWindowAdClient(windowAdClient);

            if (client.OnAdLoaded != null)
            {
                client.OnAdLoaded(client, EventArgs.Empty);
            }
        }
        private static void windowAdDidFailToLoadAdWithErrorCallback(IntPtr windowAdClient, string error)
        {
            WindowAdClient client = IntPtrToWindowAdClient(windowAdClient);

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