// Method called from UI button to buy units of a Ship.
    public void Buy()
    {
        if (currencyManager.currency >= cost * quantityMultiplier)
        {
            currencyManager.currency -= cost;
            quantity += quantityMultiplier;
            currencyManager.ChangeCurrencyIdleGain(currencyGain * quantityMultiplier);
            UpdateValues();

            if (quantity >= shipData.qtToUnlockNextShip)
            {
                UnlockNextShip();
            }

            // Play sound.
        }
        else
        {
            // Play different sound.
        }
    }