31天重构学习笔记22. 分解方法

概念：本文中的”分解方法”是指把我们所做的这个功能不停的分解方法，直到将一个大方法分解为名字有意义且可读性更好的若干个小方法。

正文：如下代码所示，因为现实中AcceptPayment方法不会做这么多的事情。，所以我们通过几次分解将 AcceptPayment拆分成若干个名字有意义且可读性更好的小方法。

using System.Collections.Generic;
using System.Linq;

namespace LosTechies.DaysOfRefactoring.SampleCode.BreakMethod.Before
{
    public class CashRegister
    {
        public CashRegister()
        {
            Tax = 0.06m;
        }

        private decimal Tax { get; set; }

        public void AcceptPayment(Customer customer, IEnumerable<Product> products, decimal payment)
        {
            decimal subTotal = 0m;
            foreach (Product product in products)
            {
                subTotal += product.Price;
            }

            foreach (Product product in products)
            {
                subTotal -= product.AvailableDiscounts;
            }

            decimal grandTotal = subTotal * Tax;

            customer.DeductFromAccountBalance(grandTotal);
        }
    }

    public class Customer
    {
        public void DeductFromAccountBalance(decimal amount)
        {
            // deduct from balance
        }
    }

    public class Product
    {
        public decimal Price { get; set; }
        public decimal AvailableDiscounts { get; set; }
    }
}

重构后的代码如下，我们把AcceptPayment的内部逻辑拆分成了CalculateSubtotal、SubtractDiscounts、AddTax、SubtractFromCustomerBalance四个功能明确且可读性更好的小方法。

using System.Collections.Generic;

namespace LosTechies.DaysOfRefactoring.SampleCode.BreakMethod.After
{
    public class CashRegister
    {
        public CashRegister()
        {
            Tax = 0.06m;
        }

        private decimal Tax { get; set; }
        private IEnumerable<Product> Products { get; set; }

        public void AcceptPayment(Customer customer, IEnumerable<Product> products, decimal payment)
        {
            decimal subTotal = CalculateSubtotal();

            subTotal = SubtractDiscounts(subTotal);

            decimal grandTotal = AddTax(subTotal);

            SubtractFromCustomerBalance(customer, grandTotal);
        }

        private void SubtractFromCustomerBalance(Customer customer, decimal grandTotal)
        {
            customer.DeductFromAccountBalance(grandTotal);
        }

        private decimal AddTax(decimal subTotal)
        {
            return subTotal * Tax;
        }

        private decimal SubtractDiscounts(decimal subTotal)
        {
            foreach (Product product in Products)
            {
                subTotal -= product.AvailableDiscounts;
            }
            return subTotal;
        }

        private decimal CalculateSubtotal()
        {
            decimal subTotal = 0m;
            foreach (Product product in Products)
            {
                subTotal += product.Price;
            }
            return subTotal;
        }
    }

    public class Customer
    {
        public void DeductFromAccountBalance(decimal amount)
        {
            // deduct from balance
        }
    }

    public class Product
    {
        public decimal Price { get; set; }
        public decimal AvailableDiscounts { get; set; }
    }
}

总结：其实这个重构和我们前面讲的“提取方法”和“提取方法对象”如出一辙，尤其是“提取方法”，所以大家只要知道用这种思想重构就行。