问题
I have following C# code in .Net 4.0. It requires a type casting of IBusiness to IRetailBusiness.
//Type checking
if (bus is IRetailBusiness)
{
//Type casting
investmentReturns.Add(new RetailInvestmentReturn((IRetailBusiness)bus));
}
if (bus is IIntellectualRights)
{
investmentReturns.Add(new IntellectualRightsInvestmentReturn((IIntellectualRights)bus));
}
Business Scenario:
I am designing a software system for and Investment Holding Company. The company has Retail business and IntellectualRights business. BookShop and AudioCDShop are examples of Retail business. EngineDesignPatent and BenzolMedicinePatent are examples of IntellectualRights business. These two business types are totally unrelated.
The investment company has a concept called InvestmentReturn (But each individual business is totally ignorant about this concept). InvestmentReturn is the profit gained from each business and it is calulated using ProfitElement. For each “Business Type” (Retail, IntellectualRights ), the ProfitElement used is different.
QUESTION
How to refactor this class design to avoid this type casting and type checking?
Abstract Investment
public abstract class InvestmentReturn
{
public double ProfitElement { get; set; }
public IBusiness Business{ get; set; }
public abstract double GetInvestmentProfit();
public double CalculateBaseProfit()
{
double profit = 0;
if (ProfitElement < 5)
{
profit = ProfitElement * 5 / 100;
}
else if (ProfitElement < 20)
{
profit = ProfitElement * 7 / 100;
}
else
{
profit = ProfitElement * 10 / 100;
}
return profit;
}
}
Extensions
public class RetailInvestmentReturn : InvestmentReturn
{
public RetailInvestmentReturn(IRetailBusiness retail)
{
Business = retail;
}
public override double GetInvestmentProfit()
{
//GrossRevenue is the ProfitElement for RetailBusiness
ProfitElement = ((IRetailBusiness)Business).GrossRevenue;
return base.CalculateBaseProfit();
}
}
public class IntellectualRightsInvestmentReturn : InvestmentReturn
{
public IntellectualRightsInvestmentReturn(IIntellectualRights intellectual)
{
Business = intellectual;
}
public override double GetInvestmentProfit()
{
//Royalty is the ProfitElement for IntellectualRights Business
ProfitElement = ((IIntellectualRights)Business).Royalty;
return base.CalculateBaseProfit();
}
}
Client
class Program
{
static void Main(string[] args)
{
#region MyBusines
List<IBusiness> allMyProfitableBusiness = new List<IBusiness>();
BookShop bookShop1 = new BookShop(75);
AudioCDShop cd1Shop = new AudioCDShop(80);
EngineDesignPatent enginePatent = new EngineDesignPatent(1200);
BenzolMedicinePatent medicinePatent = new BenzolMedicinePatent(1450);
allMyProfitableBusiness.Add(bookShop1);
allMyProfitableBusiness.Add(cd1Shop);
allMyProfitableBusiness.Add(enginePatent);
allMyProfitableBusiness.Add(medicinePatent);
#endregion
List<InvestmentReturn> investmentReturns = new List<InvestmentReturn>();
foreach (IBusiness bus in allMyProfitableBusiness)
{
//Type checking
if (bus is IRetailBusiness)
{
//Type casting
investmentReturns.Add(new RetailInvestmentReturn((IRetailBusiness)bus));
}
if (bus is IIntellectualRights)
{
investmentReturns.Add(new IntellectualRightsInvestmentReturn((IIntellectualRights)bus));
}
}
double totalProfit = 0;
foreach (var profitelement in investmentReturns)
{
totalProfit = totalProfit + profitelement.GetInvestmentProfit();
Console.WriteLine("Profit: {0:c}", profitelement.GetInvestmentProfit());
}
Console.ReadKey();
}
}
Business Domain Entities
public interface IBusiness
{
}
public abstract class EntityBaseClass
{
}
public interface IRetailBusiness : IBusiness
{
double GrossRevenue { get; set; }
}
public interface IIntellectualRights : IBusiness
{
double Royalty { get; set; }
}
#region Intellectuals
public class EngineDesignPatent : EntityBaseClass, IIntellectualRights
{
public double Royalty { get; set; }
public EngineDesignPatent(double royalty)
{
Royalty = royalty;
}
}
public class BenzolMedicinePatent : EntityBaseClass, IIntellectualRights
{
public double Royalty { get; set; }
public BenzolMedicinePatent(double royalty)
{
Royalty = royalty;
}
}
#endregion
#region Retails
public class BookShop : EntityBaseClass, IRetailBusiness
{
public double GrossRevenue { get; set; }
public BookShop(double grossRevenue)
{
GrossRevenue = grossRevenue;
}
}
public class AudioCDShop : EntityBaseClass, IRetailBusiness
{
public double GrossRevenue { get; set; }
public AudioCDShop(double grossRevenue)
{
GrossRevenue = grossRevenue;
}
}
#endregion
REFERENCES
- Refactor my code : Avoiding casting in derived class
- Cast to generic type in C#
- How a Visitor implementation can handle unknown nodes
- Open Closed Principle and Visitor pattern implementation in C#
回答1:
This solution uses the notions that business interfaces know they must create a return and that their concrete implementations know what kind of concrete return to create.
Step 1 Split InvestmentReturn into two interfaces; the original minus the Business property and a new generic subclass:
public abstract class InvestmentReturn
{
public double ProfitElement { get; set; }
public abstract double GetInvestmentProfit();
public double CalculateBaseProfit()
{
// ...
}
}
public abstract class InvestmentReturn<T>: InvestmentReturn where T : IBusiness
{
public T Business { get; set; }
}
Step 2 Inherit from the generic one so you can use Business without casting:
public class RetailInvestmentReturn : InvestmentReturn<IRetailBusiness>
{
// this won't compile; see **Variation** below for resolution to this problem...
public RetailInvestmentReturn(IRetailBusiness retail)
{
Business = retail;
}
public override double GetInvestmentProfit()
{
ProfitElement = Business.GrossRevenue;
return CalculateBaseProfit();
}
}
Step 3 Add a method to IBusiness that returns an InvestmentReturn:
public interface IBusiness
{
InvestmentReturn GetReturn();
}
Step 4 Introduce a generic sublcass of EntityBaseClass to provide the default implementation of the above method. If you don't do this you'll have to implement it for all the businesses. If you do do this it means all of your classes where you don't want to repeat the GetReturn() implementation must inherit from the class below, which in turn means they must inherit from EntityBaseClass.
public abstract class BusinessBaseClass<T> : EntityBaseClass, IBusiness where T : InvestmentReturn, new()
{
public virtual InvestmentReturn GetReturn()
{
return new T();
}
}
Step 5 Implement that method for each of your subclasses if necessary. Below is an example for the BookShop:
public class BookShop : BusinessBaseClass<RetailInvestment>, IRetailBusiness
{
public double GrossRevenue { get; set; }
public BookShop(double grossRevenue)
{
GrossRevenue = grossRevenue;
}
// commented because not inheriting from EntityBaseClass directly
// public InvestmentReturn GetReturn()
// {
// return new RetailInvestmentReturn(this);
// }
}
Step 6 Modify your Main to add the instances of InvestmentReturn. You don't have to typecast or type-check because that's already been done earlier in a type safe way:
static void Main(string[] args)
{
var allMyProfitableBusiness = new List<IBusiness>();
// ...
var investmentReturns = allMyProfitableBusiness.Select(bus => bus.GetReturn()).ToList();
// ...
}
If you don't want your concrete businesses to know anything about creating an InvestmentReturn—only knowing that they must create one when asked—then you'll probably want to modify this pattern to incorporate a factory that creates returns given input (e.g. a map between IBusiness implementations and InvestmentReturn subtypes).
Variation
All of the above works fine and will compile if you remove the investment return constructors that set the Business property. Doing this means setting Business elsewhere. That might not be desirable.
An alternative to that would be to set the Business property inside GetReturn. I found a way to do that, but it really starts to make the classes look messy. It's here for your evaluation as to whether its worth it.
Remove the non-default constructor from RetailInvestmentReturn:
public class RetailInvestmentReturn : InvestmentReturn<IRetailBusiness>
{
public override double GetInvestmentProfit()
{
ProfitElement = Business.GrossRevenue;
return CalculateBaseProfit();
}
}
Change BusinessBaseClass. This is where it gets messy with a double-cast, but at least it's limited to one place.
public abstract class BusinessBaseClass<T, U> : EntityBaseClass, IBusiness
where T : InvestmentReturn<U>, new()
where U : IBusiness
{
public double GrossRevenue { get; set; }
public virtual InvestmentReturn GetReturn()
{
return new T { Business = (U)(object)this };
}
}
Finally change your businesses. Here's an example for BookShop:
public class BookShop : BusinessBaseClass<RetailInvestmentReturn, IRetailBusiness>, IRetailBusiness
{
// ...
}
回答2:
Make the concrete implementations of IBusiness visitable by visitor pattern. then create a visitor in the investment return domain that can visit each business, like this:
public interface IVisitor<T>
{
T Visit(IIntellectualRights bus);
T Visit(IRetailBusiness bus);
}
public interface IBusiness
{
T Accept<T>(IVisitor<T> visitor);
}
public class AudioCDShop : EntityBaseClass, IRetailBusiness
{
public void Accept(IVisitor visitor)
{
return visitor.Visit(this);
}
//do the same for each IBusiness implementor.
Then in your investment return domain:
public class InvestmentVisitor : IVisitor<InvestmentReturn>
{
public InvestmentReturn GetInvestment(IBusiness bus)
{
return bus.Accept(this);
}
public InvestmentReturn Visit(IIntellectualRights bus)
{
return new IntellectualRightsInvestmentReturn(bus)
}
public InvestmentReturn Visit(IRetailBusiness bus)
{
return new RetailInvestmentReturn(bus);
}
}
Usage
var investmentReturn = new InvestmentVisitor().GetInvestment(bus);
totally untested and unverified.. but the concept works. This might also be way overkill if you only have two different kinds of nodes that should be visited.
回答3:
Basically, if I understood you right, you want to avoid the type casting.
You can accomplish that simply by changing the constructor signature from:
public RetailInvestmentReturn(IRetailBusiness retail) {...}
public IntellectualRightsInvestmentReturn(IIntellectualRights intellectual) {...}
to:
public RetailInvestmentReturn(IBusiness retail) {...}
public IntellectualRightsInvestmentReturn(IBusiness intellectual) {...}
If that is not an option due to design constraints, then you can try to use the strategy pattern. That would still need a type cast, but you would get rid of the terrifying "ifs" and "elses", that, I believe, is your real question, right? In order to do that you need to:
- Create a dictionary with the "type" and the "method to run"
- Use it!
In code, that would look something like this:
(Create,...)
Dictionary<Type,Func<IBusiness,InvestmentReturn>> dict = new Dictionary<Type, Func<IBusiness, InvestmentReturn>> { {typeof (BookShop), business => new RetailInvestmentReturn((IRetailBusiness) business)}, {typeof (AudioCDShop), business => new IntellectualRightsInvestmentReturn((IIntellectualRights) business)} };(Use it!)
// try this:
foreach (IBusiness bus in allMyProfitableBusiness)
{
investmentReturns.Add(dict[bus.GetType()](bus));
}
回答4:
Let the IBusiness interface handle the type of InvestmentReturn type and return the profit amount.
Changes to the foreach loop:
foreach (IBusiness bus in allMyProfitableBusiness)
{
// No type checking or casting. It is scalable to new business types.
investmentReturns.Add(bus.GetReturnInvestment());
}
Updates to the interfaces:
public interface IBusiness
{
IReturnInvestment GetReturnInvestment();
double GetProfit();
}
public abstract class EntityBaseClass
{
}
public interface IRetailBusiness : IBusiness
{
...
}
public interface IIntellectualRights : IBusiness
{
...
}
Business classes with another base class:
#region Intellectuals
public abstract IntellectualRightsBaseClass : EntityBaseClass, IIntellectualRights
{
...
public IReturnInvestment GetReturnInvestment()
{
return new IntellectualRightsInvestmentReturn(this);
}
public double GetProfit()
{
return this.Royalty;
}
}
public class EngineDesignPatent : IntellectualRightsBaseClass
{
...
}
public class BenzolMedicinePatent : IntellectualRightsBaseClass
{
...
}
#endregion
#region Retails
public abstract RetailBusinessBaseClass : IRetailBusiness
{
...
public IReturnInvestment GetReturnInvestment()
{
return new RetailInvestmentReturn(this);
}
public double GetProfit()
{
return this.GrossRevenue;
}
}
public class BookShop : RetailBusinessBaseClass
{
...
}
public class AudioCDShop : RetailBusinessBaseClass
{
...
}
#endregion
Extensions
public class RetailInvestmentReturn : InvestmentReturn
{
public RetailInvestmentReturn(IRetailBusiness retail)
: base(retail)
{
}
/* Don't need anymore
public override double GetInvestmentProfit()
{
//GrossRevenue is the ProfitElement for RetailBusiness
ProfitElement = Business.GetProfit();
return base.CalculateBaseProfit();
} */
}
public class IntellectualRightsInvestmentReturn : InvestmentReturn
{
public IntellectualRightsInvestmentReturn(IIntellectualRights intellectual)
: base(intellectual)
{
}
/* Don't need anymore
public override double GetInvestmentProfit()
{
//Royalty is the ProfitElement for IntellectualRights Business
ProfitElement = Business.GetProfit();
return base.CalculateBaseProfit();
} */
}
Abstract InvestmentReturn
public abstract class InvestmentReturn
{
protected InvestmentReturn(IBusiness business)
{
this.Business = business;
}
public double ProfitElement { get; set; }
public IBusiness Business{ get; set; }
public override double GetInvestmentProfit()
{
ProfitElement = this.Business.GetProfit();
return this.CalculateBaseProfit();
}
public double CalculateBaseProfit()
{
double profit = 0;
if (ProfitElement < 5)
{
profit = ProfitElement * 5 / 100;
}
else if (ProfitElement < 20)
{
profit = ProfitElement * 7 / 100;
}
else
{
profit = ProfitElement * 10 / 100;
}
return profit;
}
}
回答5:
What about making InvestmentReturn a concrete class and moving ProfitElement logic to IBusiness?
public class InvestmentReturn
{
public double ProfitElement { get; set; }
public double InvestmentProfit{ get; set; }
public RetailInvestmentReturn(IRetailBusiness bus)
{
ProfitElement = bus.GetProfitElement();
}
public double CalculateBaseProfit()
{
......
}
}
public class BenzolMedicinePatent : EntityBaseClass, IIntellectualRights
{
public double Royalty { get; set; }
public BenzolMedicinePatent(double royalty)
{
Royalty = royalty;
}
public override double GetProfitElement()
{
return royalty;
}
}
public class BookShop : EntityBaseClass, IRetailBusiness
{
public double GrossRevenue { get; set; }
public BookShop(double grossRevenue)
{
GrossRevenue = grossRevenue;
}
public override double GetProfitElement()
{
return royalty;
}
}
Now the client becomes:
class Program
{
static void Main(string[] args)
{
#region MyBusines
List<IBusiness> allMyProfitableBusiness = new List<IBusiness>();
BookShop bookShop1 = new BookShop(75);
AudioCDShop cd1Shop = new AudioCDShop(80);
EngineDesignPatent enginePatent = new EngineDesignPatent(1200);
BenzolMedicinePatent medicinePatent = new BenzolMedicinePatent(1450);
allMyProfitableBusiness.Add(bookShop1);
allMyProfitableBusiness.Add(cd1Shop);
allMyProfitableBusiness.Add(enginePatent);
allMyProfitableBusiness.Add(medicinePatent);
#endregion
List<InvestmentReturn> investmentReturns = new List<InvestmentReturn>();
foreach (IBusiness bus in allMyProfitableBusiness)
{
investmentReturns.Add(new InvestmentReturn(bus));
}
double totalProfit = 0;
foreach (var profitelement in investmentReturns)
{
totalProfit = totalProfit + profitelement.GetInvestmentProfit();
Console.WriteLine("Profit: {0:c}", profitelement.GetInvestmentProfit());
}
Console.ReadKey();
}
}
回答6:
All the answers above seem more complicated than necessary, but you don't really say exactly what information you need to keep, so it's hard to know how far one can take the re-design of your classes. If all you wanted to do was to produce the results that the above program produces and still use objects, you could do this:
class Program2
{
static void Main(string[] args)
{
List<Business> allMyProfitableBusiness = new List<Business>();
Business bookShop1 = new Business(75);
Business cd1Shop = new Business(80);
Business enginePatent = new Business(1200);
Business medicinePatent = new Business(1450);
allMyProfitableBusiness.Add(bookShop1);
allMyProfitableBusiness.Add(cd1Shop);
allMyProfitableBusiness.Add(enginePatent);
allMyProfitableBusiness.Add(medicinePatent);
foreach (var business in allMyProfitableBusiness)
{
Console.WriteLine("Profit: {0:c}", business.GetInvestmentProfit());
}
Console.ReadKey();
}
}
public class Business
{
private double ProfitElement;
public Business(double profitElement)
{
ProfitElement = profitElement;
}
public double GetInvestmentProfit()
{
double profit = 0;
if (ProfitElement < 5)
{
profit = ProfitElement * 5 / 100;
}
else if (ProfitElement < 20)
{
profit = ProfitElement * 7 / 100;
}
else
{
profit = ProfitElement * 10 / 100;
}
return profit;
}
}
If, for some reason, you do need to keep the different types of Businesses (Retail and Intellectual), you could still greatly simplify it using base classes. You don't need generics or your InvestmentReturn or EntityBaseClass (and although you calculate totalProfit, it is not used anywhere):
class Program
{
static void Main(string[] args)
{
List<Business> allMyProfitableBusiness = new List<Business>();
BookShop bookShop1 = new BookShop(75);
AudioCDShop cd1Shop = new AudioCDShop(80);
EngineDesignPatent enginePatent = new EngineDesignPatent(1200);
BenzolMedicinePatent medicinePatent = new BenzolMedicinePatent(1450);
allMyProfitableBusiness.Add(bookShop1);
allMyProfitableBusiness.Add(cd1Shop);
allMyProfitableBusiness.Add(enginePatent);
allMyProfitableBusiness.Add(medicinePatent);
double totalProfit = 0;
foreach (var business in allMyProfitableBusiness)
{
totalProfit = totalProfit + business.GetInvestmentProfit();
Console.WriteLine("Profit: {0:c}", business.GetInvestmentProfit());
}
Console.ReadKey();
}
}
public abstract class Business
{
public abstract double Profit { get; }
public double GetInvestmentProfit()
{
double profit = 0;
if (Profit < 5)
{
profit = Profit * 5 / 100;
}
else if (Profit < 20)
{
profit = Profit * 7 / 100;
}
else
{
profit = Profit * 10 / 100;
}
return profit;
}
}
public abstract class RetailBusiness : Business
{
public double GrossRevenue { get; set; }
public override double Profit {get {return GrossRevenue; } }
}
public abstract class IntellectualRights : Business
{
public double Royalty { get; set; }
public override double Profit {get {return Royalty; } }
}
#region Intellectuals
public class EngineDesignPatent : IntellectualRights
{
public EngineDesignPatent(double royalty)
{
Royalty = royalty;
}
}
public class BenzolMedicinePatent : IntellectualRights
{
public BenzolMedicinePatent(double royalty)
{
Royalty = royalty;
}
}
#endregion
#region Retails
public class BookShop : RetailBusiness
{
public BookShop(double grossRevenue)
{
GrossRevenue = grossRevenue;
}
}
public class AudioCDShop : RetailBusiness
{
public AudioCDShop(double grossRevenue)
{
GrossRevenue = grossRevenue;
}
}
#endregion
Of course, the chances that anyone will read this are very, very small :-)
来源：https://stackoverflow.com/questions/21482850/refactoring-code-to-avoid-type-casting