Question

Let’s say I have declared the following classes:

class BaseClass{
    /* properties, constructors, getters, setters etc. */

    public static BaseClass Create(string url){
    /*will return, depending on url, a BaseClass or a SubClass object*/
    }

    public void Method(){
    /* some code here */
    }
}

class SubClass: BaseClass{
    /* other properties, constructors, getters, setters etc. */

    new public void Method(){
    /* some other code here */
    }
}

Now in my Main method I would like to do something along the lines of:

BaseClass baseClass = BaseClass.Create(url);
if(baseClass.GetType()==typeof(SubClass)){ 
    baseClass.Method();
}

The idea here, of course, is to use Method as it is implemented in SubClass. It may be a silly question but how do I do that? I can’t cast a base class into a subclass so I’m not sure…

EDIT

Clarified my question. Even though baseClass was declared as a BaseClass instance, baseClass is SubClass will return trueif url is such that Create returns a SubClass instance.

Answer 1

It looks like you might be looking for polymorphism, but I can’t be sure from the description. What is the concrete use case for what you’re trying to do?

class BaseClass{

    public virtual void Method(){
        Console.WriteLine("BaseClass");
    }
}

class SubClass : BaseClass{
    /* other properties, constructors, getters, setters etc. */

    public override void Method(){
        Console.WriteLine("SubClass");
    }
}

static class Test
{
    public void go() {
        BaseClass instance = new SubClass();
        instance.Method(); // prints "SubClass"
    }
}

If it doesn’t make sense for the base class to have an implementation, then declare the class and the method as abstract — this forces the derived classes to override the method, guaranteeing that any instantiated class instance will have a valid implementation.