第13天:提取方法对象

这个重构建议是对第10天:提取方法的继续

我们在一个类中提取出来了大量的私有方法和变量,会造成这个类臃肿不堪,难以阅读

因此最好提取出来方法对象,用以将功能的一个个逻辑分离开

旧的代码:

   public class OrderInfo
    {
        public decimal Price { get; private set; }
    }
    public class Order
    {
        private IList<OrderInfo> OrderLineItems { get; set; }
        private IList<decimal> Discounts { get; set; }
        private decimal Tax { get; set; }
        public decimal Calculate()
        {
            decimal subTotal = 0m;
            // Total up line items
            foreach (OrderInfo lineItem in OrderLineItems)
            {
                subTotal += lineItem.Price;
            }
            // Subtract Discounts
            foreach (decimal discount in Discounts)
                subTotal -= discount;
            // Calculate Tax
            decimal tax = subTotal * Tax;
            // Calculate GrandTotal
            decimal grandTotal = subTotal + tax;
            return grandTotal;
        }
    }

 

重构后的代码,我们通过构造方法,将返回计算结果的类的引用传递给包含多个计算方法的新建对象，或者向方法对象的构造函数中单独传递各个参数。

:

    public class OrderInfo
    {
        public decimal Price { get; private set; }
    }
    public class Order
    {
        public IEnumerable<OrderInfo> OrderLineItems { get; private set; }
        public IEnumerable<decimal> Discounts { get; private set; }
        public decimal Tax { get; private set; }
        public decimal Calculate()
        {
            return new OrderCalculator(this).Calculate();
        }
    }
    public class OrderCalculator
    {
        private decimal SubTotal { get; set; }
        private IEnumerable<OrderInfo> OrderLineItems { get; set; }
        private IEnumerable<decimal> Discounts { get; set; }
        private decimal Tax { get; set; }
        public OrderCalculator(Order order)
        {
            OrderLineItems = order.OrderLineItems;
            Discounts = order.Discounts;
            Tax = order.Tax;
        }
        public decimal Calculate()
        {
            CalculateSubTotal();
            SubtractDiscounts();
            CalculateTax();
            return SubTotal;
        }
        private void CalculateSubTotal()
        {
            // Total up line items
            foreach (OrderInfo lineItem in OrderLineItems)
                SubTotal += lineItem.Price;
        }
        private void SubtractDiscounts()
        {
            // Subtract Discounts
            foreach (decimal discount in Discounts)
                SubTotal -= discount;
        }
        private void CalculateTax()
        {
            // Calculate Tax
            SubTotal += SubTotal * Tax;
        }
    }