将基类转换为派生类

Question

在C#中是否可以将基类对象显式转换为其派生类之一？目前我认为我必须为我的派生类创建一个构造函数,它接受一个基类对象作为参数并复制属性值.我真的不喜欢这个想法,所以我想尽可能避免它.

这似乎不应该工作(对象被实例化为新的基础,因此不应该为派生类的额外成员分配内存)但是C#似乎允许我这样做:

class BaseClass
{
  ... some stuff ...
}

class DerivedClass : BaseClass
{
    public bool MyDerivedProperty{ get; set; }
}


static void Main(string[] args)
{
    BaseClass myBaseObject = new BaseClass();
    DerivedClass myDerivedObject = myBaseObject as DerivedClass;

    myDerivedObject.MyDerivedProperty = true;
}

Answer 1

不,没有像你说的那样转换类的内置方法.最简单的方法是执行您的建议:创建DerivedClass(BaseClass)构造函数.其他选项基本上可以自动将属性从基础复制到派生实例,例如使用反射.

你发布的代码as将编译,因为我确定你已经看到了,但是当你运行它时会抛出一个空引用异常,因为它myBaseObject as DerivedClass会计算null,因为它不是一个实例DerivedClass.

Answer 2

那是不可能的.但您可以使用像AutoMapper这样的Object Mapper

例:

class A
{
    public int IntProp { get; set; }
}
class B
{
    public int IntProp { get; set; }
    public string StrProp { get; set; }
}

在global.asax或应用程序启动中:

AutoMapper.Mapper.CreateMap<A, B>();

用法:

var b = AutoMapper.Mapper.Map<B>(a);

它可以通过流畅的API轻松配置.

Answer 3

我找到了一个解决方案,并不是说它是最好的解决方案,但它对我来说很干净,并且不需要对我的代码进行任何重大更改.我的代码看起来与你的相似,直到我意识到它不起作用.

我的基础班

public class MyBaseClass
{
   public string BaseProperty1 { get; set; }
   public string BaseProperty2 { get; set; }
   public string BaseProperty3 { get; set; }
   public string BaseProperty4 { get; set; }
   public string BaseProperty5 { get; set; }
}

我的衍生课程

public class MyDerivedClass : MyBaseClass
{
   public string DerivedProperty1 { get; set; }
   public string DerivedProperty2 { get; set; }
   public string DerivedProperty3 { get; set; }
}

获取填充基类的先前方法

public MyBaseClass GetPopulatedBaseClass()
{
   var myBaseClass = new MyBaseClass();

   myBaseClass.BaseProperty1 = "Something"
   myBaseClass.BaseProperty2 = "Something else"
   myBaseClass.BaseProperty3 = "Something more"
   //etc...

   return myBaseClass;
}

在我尝试这个之前,这让我无法抛出错误

public MyDerivedClass GetPopulatedDerivedClass()
{
   var newDerivedClass = (MyDerivedClass)GetPopulatedBaseClass();

   newDerivedClass.UniqueProperty1 = "Some One";
   newDerivedClass.UniqueProperty2 = "Some Thing";
   newDerivedClass.UniqueProperty3 = "Some Thing Else";

   return newDerivedClass;
}

我改变了我的代码,如下所示,它似乎工作,现在更有意义:

旧

public MyBaseClass GetPopulatedBaseClass()
{
   var myBaseClass = new MyBaseClass();

   myBaseClass.BaseProperty1 = "Something"
   myBaseClass.BaseProperty2 = "Something else"
   myBaseClass.BaseProperty3 = "Something more"
   //etc...

   return myBaseClass;
}

新

public void FillBaseClass(MyBaseClass myBaseClass)
{
   myBaseClass.BaseProperty1 = "Something"
   myBaseClass.BaseProperty2 = "Something else"
   myBaseClass.BaseProperty3 = "Something more"
   //etc...
}

旧

public MyDerivedClass GetPopulatedDerivedClass()
{
   var newDerivedClass = (MyDerivedClass)GetPopulatedBaseClass();

   newDerivedClass.UniqueProperty1 = "Some One";
   newDerivedClass.UniqueProperty2 = "Some Thing";
   newDerivedClass.UniqueProperty3 = "Some Thing Else";

   return newDerivedClass;
}

新

public MyDerivedClass GetPopulatedDerivedClass()
{
   var newDerivedClass = new MyDerivedClass();

   FillBaseClass(newDerivedClass);

   newDerivedClass.UniqueProperty1 = "Some One";
   newDerivedClass.UniqueProperty2 = "Some Thing";
   newDerivedClass.UniqueProperty3 = "Some Thing Else";

   return newDerivedClass;
}

Answer 4

您可以自己实现转换,但我不建议这样做.如果要执行此操作,请查看装饰器模式以扩展现有对象的功能.