Virtual functions

Question

I don\'t really understand - when am I supposed to use virtual functions?I\'ll be glad if someone could explain it to me, thanks.

Answer 1

probably easiest to understand through an example So imagin we have code like below

class Base{
public virtual string VirtualMethod(){
    return "base virtual";
}

public string NotVirtual(){
    return "base non virtual";
}
}

class Derived : Base{
  public override string VirtualMethod(){
        return "Derived overriden";
  }
  public new string NotVirtual(){
        return "new method defined in derived";
  }
}

}

if you use the code as below

  Base b = new Base();
  Derived d = new Derived();
  Base b2 = d;

  Console.WriteLine(b.VirtualMethod());
  Console.WriteLine(d.VirtualMethod());
  Console.WriteLine(b2.VirtualMethod());

  Console.WriteLine(b.NotVirtual());
  Console.WriteLine(d.NotVirtual());
  Console.WriteLine(b2.NotVirtual());

It's worth paying attention to that b2 a d is the exact same object!

the result of the above would be:

base virtual

Derived overriden

Derived overriden

base non virtual

new method defined in derived

base non virtual

Eventhough the last two lines call a method name NotVirtual on the same object. Because te variables are declared of Base and Derived and the method is not virtual the declared type of the variable determine the method called whereas if the method is virtual the runtime type of the object is the determining factor for which method that will be called