What are the dangers of making a method virtual?

Question

I\'ve been doing some mocking with RhinoMocks and it requires that mocked methods be made virtual. This is fine except we have a custom framework which contains the methods

Answer 1

Actually it can be very problematic if the method is not designed to be overridden and someone overrides it. In particular, never call a virtual method from a constructor. Consider:

class Base {
    public Base() {
       InitializeComponent();
    }
    protected virtual void InitializeComponent() {
        ...
    }
}

class Derived : Base {
    private Button button1;
    public Derived() : base() {
        button1 = new Button();
    }
    protected override void InitializeComponent() {
        button1.Text = "I'm gonna throw a null reference exception"
    }
}

The Derived class may not be aware that the virtual method call will result in its InitializeComponent method being called before a single line of its own constructor has run.