步步为营 .NET 代码重构学习笔记六、移动函数和移动值域(Move Method And Move Field)

Move Method

概述

程序中，有个函数与其所驻class之外的另一个class进行更多交流，调用后者或被后者调用

动机（Motivation）

如果一个class有太多行为，或如果一个class与另一个class有太多合作而形成高度耦合（highly coupled），我们就会搬移函数。通过这种手段，我们可以使系统中的classes更简单，这些classes最终也将更干净利落地实现系统交付的任务。

示例

public class MoveMethod
  { 
      private AccountType _type;
      private int _daysOverdrawn;
      public double OverDraftCharge()
      {
          if (_type.IsPremium())
          {
              double result = 10;
              if (_daysOverdrawn > 7)
                  result += (_daysOverdrawn - 7) * 0.85;
              return result;
          }
          else
              return _daysOverdrawn * 1.75;
      }
      public double BankCharge()
      {
          double result = 4.5;
          if (_daysOverdrawn > 0)
              result += OverDraftCharge();
          return result;
      }
  }
 
  public class AccountType
  {
      public bool IsPremium()
      {
          return true;
      }
  }

改为

public class MoveMethod
{
    private AccountType _type;
 
    public double BankCharge()
    {
        double result = 4.5;
        if (_type._daysOverdrawn > 0)
            result += _type.OverDraftCharge();
        return result;
    }
}
 
public class AccountType
{
    private int _daysOverdrawn;
 
    public int DaysOverdrawn
    {
        get { return _daysOverdrawn; }
        set { _daysOverdrawn = value; }
    }
 
    public bool IsPremium()
    {
        return true;
    }
 
    public double OverDraftCharge()
    {
        if (IsPremium())
        {
            double result = 10;
            if (_daysOverdrawn > 7)
                result += (_daysOverdrawn - 7) * 0.85;
            return result;
        }
        else
            return _daysOverdrawn * 1.75;
    }
}

Move Field（搬移值域）

概述

在target class建立一个new field，修改source field的所有用户，令它们改用new field。

动机（Motivation）

对于一个field（值域），在其所驻class之外的另一个class中有更多函数使用了它，我就会考虑搬移这个field。

示例

public class MoveMethod
{
    private AccountType _type;
    private double _interestRate;
    public double InterestForAmountDay(double amount,int days)
    {
        return _interestRate * amount * days / 365;
    }
}
 
public class AccountType
{
 
}

改为

public class MoveMethod
{
    private AccountType _type;
 
    public double InterestForAmountDay(double amount, int days)
    {
        return _type.InterestRate * amount * days / 365;
    }
}
 
public class AccountType
{
    private double _interestRate;
    public double InterestRate
    {
        get { return _interestRate; }
        set { _interestRate = value; }
    }
}