需要一个设计模式来删除对象创建中的枚举和切换语句 [英] Need a design pattern to remove enums and switch statement in object creation

问题描述

假设我正在创建一个运动游戏，在这个游戏中，玩家可以玩各种各样的位置，攻击，防御等。
所以我首先创建一个基础类：

  public abstract class Position 
 {
 public abstract string Name 
 {
 get; 
} 
} 
  

和子类...

  public class Defender：Position 
 {
 public override string Name 
 {
 get {return卫士; } 
} 
} 
  

等等。这是很好的。

但现在我需要一个函数来创建这些对象。我需要通过位置函数创建。所以一个可能的解决方案是创建一个所有位置的枚举，并将该值传递给一个打开枚举并返回相应对象的函数。但这会触发我的代码气味报警。这个soultion将一个函数中的类，枚举和开关连接在一起：

  public static Position GetByType（Types position）
 {
 switch（position）
 {
 case Types.Defender：
 return new Defender（）; 
 ...还有可怕的代码
  

我应该查看什么解决方案？这是哪种设计模式？

解决方案

如果你必须小规模地做到这一点，交换机不是很糟糕，特别是如果它居住在一个地方。

如果你必须在中等规模的情况下，你可能想考虑改进内部的一些 - Steve Ellinger的建议是一个合理的。我个人喜欢使用 IDictionary< MyEnum，Action< T> 其中Action返回有问题的类的新实例。

如果您必须以大规模或可配置的规模执行此操作，您应该可以查看一个IoC控制器，如结构图或ninject或任何酷的孩子们玩这些天。

Let's say I am creating a sports game, and in this game there are various positions a player can play, attack, defence, etc. So I start by creating a base class:

public abstract class Position
{
 public abstract string Name
 {
  get;
 }
}

and the subclasses...

public class Defender : Position
{
 public override string Name
 {
  get { return "Defender"; }
 }
}

and so on. This is all fine.

But now I need a function to create these objects. I need a create by position function. So one possible solution is to create an enum of all the positions and pass this value to a function that switches on the enum and returns the appropriate object. But this triggers my code smell alarm. This soultion ties together the classes, the enum and the switch inside a function:

public static Position GetByType(Types position)
{
 switch(position)
 {
  case Types.Defender:
   return new Defender();
... and further terrible code

What solution should I be looking at? Which design pattern is this?

解决方案

If you have to do this on a small scale, the switch isn't really bad, especially if it lives in a single place.

If you have to do this on a medium scale, you might want to consider improving the internals a bit -- Steve Ellinger's suggestion is a reasonable one. Personally I prefer to use a IDictionary<MyEnum, Action<T>> where the Action returns a new instance of the class in question.

If you have to do this on a grand or configurable scale, you should probably check out an IoC controller such as structuremap or ninject or whatever the cool kids are playing with these days.

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