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The message map is MFC's way of avoiding the lengthy vtables that would be required
if every class had a virtual function for every possible message it might receive.
Any class derived from CCmdTarget can contain a message map.

1. Declare the message map by adding a DECLARE_MESSAGE_MAP statement to the class declaration.
2. Implement the message map by placing macros identifying the messages that the class will handle
   between calls to BEGIN_MESSAGE_MAP and END_MESSAGE_MAP.
3. Add member functions to handle the messages.

• declare

DECLARE_MESSAGE_MAP()

• impl

BEGIN_MESSAGE_MAP(CMyApp, CWinApp)
    ON_COMMAND(ID_HELP, &CWinApp::OnHelp)
END_MESSAGE_MAP()

begin message map

BEGIN_MESSAGE_MAP( theClass, baseClass )

Parameters:

• theClass

Specifies the name of the class whose message map this is.

• baseClass

Specifies the name of the base class of theClass.

Modify CMyApp

MyApp.cpp

• OnHelp()

#include "stdafx.h"

Copy stdafx.h and targetver.h to the project directory.

afxwin

MyApp.h

Use

#ifndef __AFXWIN_H__
    #error "include 'stdafx.h' before including this file for PCH"
#endif

instead of

#include <afxwin.h>

Example

• MyApp.h

#pragma once

#ifndef __AFXWIN_H__
#error "include 'stdafx.h' before including this file for PCH"
#endif

class CMyApp :
	public CWinApp
{
public:
	CMyApp();

// Overrides
public:
	virtual BOOL InitInstance();

	// Implementation

	DECLARE_MESSAGE_MAP()
};

• MyApp.cpp

#include "stdafx.h"
#include "MyApp.h"
#include "MainWindow.h"

BEGIN_MESSAGE_MAP(CMyApp, CWinApp)
	ON_COMMAND(ID_HELP, &CWinApp::OnHelp)
END_MESSAGE_MAP()

CMyApp::CMyApp()
{
}


BOOL CMyApp::InitInstance()
{
	m_pMainWnd = new CMainWindow();
	m_pMainWnd->ShowWindow(SW_SHOW);
	m_pMainWnd->UpdateWindow();
	return TRUE;
}

CMyApp myApp;

Ref

• Message Map Macros (MFC)