重构第22天 分解方法(Break Method)

理解：如果一个功能，里面比较复杂，代码量比较多，我们就可以把这个功能分解成多个小的method，每个方法实现该功能的一个小小的部分，并且方法命名成容易理解，和方法内容相关的名称，更有助于维护和可读性提高。

详解：

重构前代码：

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

 namespace ReflectorDemo
 {
     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; }
     }
 }

我们看到这个AcceptPayment方法，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。

重构后代码：

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

 namespace ReflectorDemo
 {
     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; }
     }
 }

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。

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。