MFC message maps

MFC Message Maps:
MFC provides an alternative to the switch statement used in traditional Windows programs to handle messages sent to a window. A mapping from messages to member-functions may be defined so that when a message is to be handled by a window, the appropriate member function is called automatically.

This message-map facility is designed to be similar to virtual functions but has additional benefits not possible with C++ virtual functions.


Defining a Message Map:

1.The DECLARE_MESSAGE_MAP macro declares three members for a class.

A private array of AFX_MSGMAP_ENTRY entries called _messageEntries,


A protected AFX_MSGMAP structure called messageMap that points to the _messageEntries array


A protected virtual function called GetMessageMap that returns the address of messageMap.
This macro should be placed in the declaration of any class using message maps. By convention, it is at the end of the class declaration. For example:

class CMyWnd : public CMyParentWndClass
{
// my stuff...

protected:
//{{AFX_MSG(CMyWnd)
afx_msg void OnPaint();
//}}AFX_MSG

DECLARE_MESSAGE_MAP()
};


The message map's table is defined with a set of macros that expand to message map
entries. A table begins with a BEGIN_MESSAGE_MAP macro call, which defines the class that is handled by this message map and the parent class to which unhandled messages are passed. The
table ends with the END_MESSAGE_MAP macro call.

Between these two macro calls is an entry for each message to be handled by this message map. Every standard Windows message has a macro of the form ON_WM_xxx (where xxx is the name of the message) that generates an entry for that message.