To change the way a component handles a particular message, you override the message-handling method for that message. If the component does not already handle the particular message, you need to declare a new message-handling method. 

To override a message-handling method, you declare a new method in your component with the same message index as the method it overrides. Do not use the override directive; you must use the message directive and a matching message index. 

Note that the name of the method and the type of the single var parameter do not have to match the overridden method. Only the message index is significant. For clarity, however, it is best to follow the convention of naming message-handling methods after the messages they handle.

BEGIN_MESSAGE_MAP
  MESSAGE_HANDLER(parameter1, parameter2, parameter3)
END_MESSAGE_MAP