public static PolygonMarkerPage GetInstance()
        {
            lock (_lock)
            {
                if (instance == null)
                {
                    instance = new PolygonMarkerPage();
                }

                return(instance);
            }
        }
 protected override void OnDisappearing()
 {
     instance = null;
     base.OnDisappearing();
 }
 protected override bool OnBackButtonPressed()
 {
     instance = null;
     return(base.OnBackButtonPressed());
 }