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 that I want to mock which are currently not marked as virtual.

I can’t forsee any problem with making these methods virtual but I was wondering what are some potential dangers of making methods virtual that I should look out for?

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.