public static void Start(string trackingId, string appName, string appVersion, string clientId, string userId)
        {
            if (tracker == null)
            {
                tracker = new GoogleAnalyticsTracker();
            }

            tracker.TrackingId = trackingId;
            tracker.AppName    = appName;
            tracker.AppVersion = appVersion;
            tracker.ClientId   = clientId;
            tracker.UserId     = userId;
        }
 public static void Stop()
 {
     tracker = null;
 }