我有基类的BaseClass 和派生类 DerivedA ， DerivedB 和 DerivedC 所有继承的BaseClass 。

I have base class BaseClass and derived classes DerivedA, DerivedB, and DerivedC that all inherit BaseClass.

我有另一个类， ExternalClass 与接受类型的参数的BaseClass ，但实际上是通过一种方法派生类。什么是这些类 ExternalClass 之间的区别，如果我想在此基础上收到的派生类？

I have another class, ExternalClass with a method that accepts a parameter of type BaseClass, but is actually passed a derived class. What is the best way to differentiate between these classes in ExternalClass if I wanted to perform a different action based on which derived class it received?

我在想这样做一个选择，但我不完全知道如何。

I was thinking of doing a Select but I'm not exactly sure how.

推荐答案

您设计的很可能是有缺陷的。你应该考虑的行为的BaseClass 的方法并覆盖它在每一个派生类。你不应该检查对象的实际类型。

Your design is very likely to be flawed. You should consider making the behavior a method of BaseClass and override it in each derived class. You shouldn't check for the actual type of the object.

也就是说， ExternalClass 应该只是调用的BaseClass 声明的方法无论实际类型。由于该方法是由派生类重写，相应的执行将被调用。

That is, ExternalClass should just call a method declared in BaseClass regardless of the actual type. Since the method is overriden by derived classes, the appropriate implementation will be called.

这是说，检查对象是一个类型或其派生类的一个实例，您可以使用是操作符：

That said, to check if an object is an instance of a type or its derived classes, you can use the is operator:

if (obj is DerivedA) // C#
If TypeOf obj Is DerivedA Then ' // VB

如果要检查，如果对象是一个特定类型的实例（而不是其派生类型）：

If you want to check if the object is an instance of a specific type (and not its derived types):

if (obj.GetType() == typeof(DerivedA)) // C#
If obj.GetType() Is GetType(DerivedA) Then ' // VB