// Adds given weapon select as invoker of Swap Weapon UI event
 public static void AddSwapWeaponUIInvoker(WeaponSelect invoker)
 {
     // adds invoker to list and adds all listeners to this invoker
     swapWeaponUIInvokers.Add(invoker);
     foreach (UnityAction <int> listener in swapWeaponUIListeners)
     {
         invoker.AddSwapWeaponUIListener(listener);
     }
 }