public override void OnWindowFocusChanged(bool hasFocus)
        {
            if (customProgressDialog == null)
            {
                return;
            }

            ImageView         imageView         = customProgressDialog.FindViewById <ImageView>(Resource.Id.loadingImageView);
            AnimationDrawable animationDrawable = (AnimationDrawable)imageView.Background;

            animationDrawable.Start();
            base.OnWindowFocusChanged(hasFocus);
        }