Question

I have a product class in C# that inherits from another product class

using ExternalAssemb.ProductA;

public class MyProduct : ProductA
{
    //....
}

I’m trying to do an explicit cast from ProductA that is in a DLL I reference but it’s telling me it’s unable to cast

MyProduct myProduct = (MyProduct)productAobject;

Result:: System.InvalidCastException: Unable to cast object of type ‘ExternalAssemb.ProductA’ to type ‘MyAssembly.MyProduct’.

What am I doing wrong?

Answer 1

You can cast a ProductA reference to a MyProduct reference, but only if it actually points to MyProductA or a child thereof.

What you’re doing is trying to treat the parent like a child, that’s doesn’t work. Rather, you can treat the child like the parent, because it is like the parent.

Think of a generic example where a base class is called Shape and has children such as Square and Circle. Given a Shape reference, you can assign any child to it. But if the reference refers to a Circle, you can’t cast it to a Square. This makes sense, because all circles are shapes, but no circles are squares.

Hope the examples help.