CODEWITHSUNDEEP
c#
guidupuy
guidupuy

Reputation: 33

Using a subclass method on a base class object

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.

Upvotes: 3

Views: 3747

Answers (4)

Matyas
Matyas

Reputation: 13702

First of all: you have to initialise your variable as an instance of SubClass, otherwise there is no way.

Then declare the method in the base class virtual,

or

cast the object to SubClass, and call the Method that way.

So either

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

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

or

 ((SubClass)baseClass).Method();

Upvotes: 0

Mark Simpson
Mark Simpson

Reputation: 23365

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.

Upvotes: 2

alex
alex

Reputation: 1278

Well I don't know why you would want to do that?
There is no way that the type of an instance of BaseClass will be equal to the type of SubClass.

That could only be possible if you created a instance of SubClass and then cast it to BaseClass. But in that case you could just cast it back to SubClass to call Method()

Upvotes: 2

khellang
khellang

Reputation: 18102

If you instansiate the baseClass as BaseClass you will not be able to call the method as SubClass, but if you write

BaseClass baseClass = new SubClass();
if (baseClass is SubClass)
{
    SubClass subClass = baseClass as SubClass;
    subClass.Method();
}

it will call the method as the SubClass is defined.

Upvotes: 1

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