async void BuscarFormaPago_Tapped(object sender, EventArgs e)
 {
     //Llama al popup cuando oprime el boton de la lupa
     try
     {
         var popup = new PopupVarios("FORMA_PAGO");
         popup.CallbackEvent += OnPopupUnitsCallback;
         await PopupNavigation.Instance.PushAsync(popup);
     }
     catch (Exception ex)
     {
         throw ex;
     }
 }
 async void BuscarIVA(object sender, ItemTappedEventArgs e)
 {
     //Busqueda el Iva articulo o servicio
     if (!string.IsNullOrEmpty(txtTantoPorcierto.Text))
     {
         try
         {
             var popup = new PopupVarios("IVA");
             popup.CallbackEvent += OnPopupUnitsCallbackVarios;
             await PopupNavigation.Instance.PushAsync(popup);
         }
         catch (Exception ex)
         {
             await DisplayAlert("Aviso", ex.Message, "OK");
         }
     }
     else
     {
         await Application.Current.MainPage.DisplayAlert("Aviso", "No hay articulo o servicio para buscar.", "OK");
     }
 }