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如何将C类“转换”为具有只读属性的子类[duplicate]

polymorphism architecture c#

Bob Tway · 技术社区 · 6 年前

这似乎不应该工作(object被实例化为new base,因此不应该为派生类的额外成员分配内存),但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;
}

0 回复 | 直到 12 年前

101

Tim S. 12 年前

不,没有像你说的那样转换类的内置方法。最简单的方法是按照您的建议来做:创建一个 DerivedClass(BaseClass) 建造师。其他选项基本上是自动将属性从基复制到派生实例,例如使用反射。

你发布的代码 as 将编译,我确信您已经看到了,但是当您运行它时会抛出一个空引用异常,因为 myBaseObject as DerivedClass null ,因为它不是 DerivedClass .

Mahmood Dehghan 9 年前

那是不可能的。但是你可以使用像这样的对象映射器 AutoMapper

例子:

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

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

用法:

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

它很容易通过一个流畅的API进行配置。

rr- 11 年前

我的基类

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; }
}

我的派生类

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

获取填充基类的上一个方法

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,这给了我一个无法投射的错误

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

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

   return newDerivedClass;
}

公共MyBaseClass GetPopulatedBaseClass()
{
var myBaseClass=新建myBaseClass();

myBaseClass.BaseProperty2=“其他东西”
myBaseClass.BaseProperty3=“更多”
//等等。。。

返回myBaseClass;

新的

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

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

newDerivedClass.UniqueProperty1=“某个人”;
newDerivedClass.UniqueProperty3=“其他一些东西”;

返回newDerivedClass;
}

新的

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

   FillBaseClass(newDerivedClass);

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

   return newDerivedClass;
}

Matthias Meid 12 年前

您可以自己实现转换,但我不建议这样做。看看 Decorator Pattern

Erix 12 年前

不,没有内置转换。

另外,由于基类不是DerivedClass,myDerivedObject将为null,并且上面最后一行将抛出null ref异常。

Jan P. 12 年前

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

    myDerivedObject.MyDerivedProperty = true;
}