private void CityComboBox_SelectedIndexChanged(object sender, EventArgs e)
 {
     if (CityComboBox.SelectedIndex == -1)
     {
         LoadAd();
     }
     else
     {
         try
         {
             DgwIlan.DataSource = _adService.GetAdByCity(Convert.ToInt32(CityComboBox.SelectedValue));
         }
         catch
         {
         }
     }
 }