使用一个枚举来选择哪一个类实例 [英] Use an enum to select which class to instantiate

问题描述

我有我试图关联到DTO的一个枚举：

I have an enum that I am trying to associate to dto's:

 public enum DtoSelection
 {
     dto1,
     dto2,
     dto3,
 }

有在此枚举108和值

我为每个DTO的一个DTO对象：

I have a dto object for each of these dto's:

 public class dto1 : AbstractDto
 {
       public int Id { get; set; }
       //some stuff specific to this dto
 }

我想使一个方法（最终服务），将返回箱中的问题关联到所述DTO的类型的新DTO对象

I am trying to make a method (eventually a service) that will return me a new dto object of the type associated to the the dto in question:

 private AbstractDto(int id)
 {
      if (id == DtoSelection.Dto1.ToInt()) //extension method I wrote for enums
            return new Dto1();
      if (id == DtoSelection.Dto2.ToInt())
            return new Dto2();
 }

显然，我不希望这样做108次。无论出于何种原因，我的大脑只是缺少明显的东西。什么是处理这个问题的最好办法。

Obviously I do not want to do this 108 times. For whatever reason my brain is just missing something obvious. What is the best way to handle this.

推荐答案

这个类会做的DTO类在同一个命名空间AbstractDto定义你想，只要什么（你会需要调整它，如果没有）：

This class will do what you want as long as the Dto classes are defined in the same namespace as AbstractDto (you'll need to tweak it if not):

由于以下枚举和类：

public enum DtoSelection
{
    Dto1,
    Dto2,
    Dto3,
}

public abstract class AbstractDto
{
}

public class Dto1 : AbstractDto
{
}

public class Dto2 : AbstractDto
{
}

public class Dto3 : AbstractDto
{
}

这方法解决这些问题：

public static class DtoFactory
{
    public static AbstractDto Create(DtoSelection dtoSelection)
    {
        var type = Type.GetType(typeof(AbstractDto).Namespace + "." + dtoSelection.ToString(), throwOnError: false);

        if (type == null)
        {
            throw new InvalidOperationException(dtoSelection.ToString() + " is not a known dto type");
        }

        if (!typeof(AbstractDto).IsAssignableFrom(type))
        {
            throw new InvalidOperationException(type.Name + " does not inherit from AbstractDto");
        }

        return (AbstractDto)Activator.CreateInstance(type);
    }
}

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