private async void GpsLocationUpdateRequested(object sender, EventArgs e)
        {
            var filter = (TherapistFilter)BindingContext;
            var cell   = (ImageCell)sender;

            if (GPSLocation.IsNullOrSpecial(filter.UserLocation))
            {
                cell.IsEnabled = false;
                try
                {
                    await UpdateLocation();
                }
                finally
                {
                    cell.IsEnabled = true;
                }
            }
            else
            {
                filter.UserLocation = null;
            }
        }