C＃转换列表< ObjBase>作为List< Obj> [英] C# Casting a List<ObjBase> as List<Obj>

问题描述

为什么我不能将 List< ObjBase> 作为 List< Obj> 为什么以下无效：

Why can I not cast a List<ObjBase> as List<Obj>? Why does the following not work:

internal class ObjBase
   {
   }

internal class Obj : ObjBase
   {
   }   

internal class ObjManager
{
    internal List<Obj> returnStuff()
    {
       return getSomeStuff() as List<Obj>;
    }

    private List<ObjBase> getSomeStuff()
    {
       return new List<ObjBase>();
    }

}

internal class ObjBase
   {
   }

internal class Obj : ObjBase
   {
   }

internal class ObjManager
{
    internal List<Obj> returnStuff()
    {
       List<ObjBase> returnedList = getSomeStuff();
       List<Obj> listToReturn = new List<Obj>(returnedList.Count);
       foreach (ObjBase currentBaseObject in returnedList)
       {
          listToReturn.Add(currentBaseObject as Obj);
       }
       return listToReturn;
    }

    private List<ObjBase> getSomeStuff()
    {
       return new List<ObjBase>();
    }
}

我在Visual Studio 2008中收到以下错误为可读性）：

I get the following error in Visual Studio 2008 (shortened for readability):

无法通过引用转换，装箱转换，拆箱转换，或空类型转换

Cannot convert type 'List' to 'List' via a reference conversion, boxing conversion, unboxing conversion, wrapping conversion, or null type conversion

感谢。

推荐答案

请查看以下问题：

.NET Casting Generic List

为什么此通用投射失败？

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