private async void Cb_countries_SelectionChanged(object sender, SelectionChangedEventArgs e)
 {//select country
     try
     {
         if (cb_countries.SelectedIndex != -1)
         {
             dpnl_agent.IsEnabled = true;
             await FillCombo.fillAgentByCountry(cb_agents, (int)cb_countries.SelectedValue);
         }
         else
         {
             dpnl_agent.IsEnabled    = false;
             cb_agents.SelectedIndex = -1;
         }
         await Search();
     }
     catch (Exception ex)
     {
         HelpClass.ExceptionMessage(ex, this);
     }
 }