private void checkBox_Click(object sender, RoutedEventArgs e)
 {
     City = this.CityText.Text;
     if (checkBox.IsChecked == true)
     {
         if (loadedData.cityExists(City) == true)
         {
             if (PomocniFavourites.Contains(City.ToUpper()) == false)
             {
                 Favourites.Add(City);
                 PomocniFavourites.Add(City.ToUpper());
                 if (Favourites.Count() == 6)
                 {
                     Favourites.RemoveAt(0);
                     PomocniFavourites.RemoveAt(0);
                 }
                 this.errorMessage.Content = "";
             }
             else
             {
                 this.errorMessage.Content = "City is already added to favourites.";
             }
         }
         else
         {
             this.errorMessage.Content = "City couldn't be added to favourites. Please check the spelling and internet connection.";
         }
     }
     else
     {
         this.errorMessage.Content = "";
     }
     WriteFavorites();
 }