Using ON_UPDATE_COMMAND_UI with menu items and controls

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Warning: The class presented in this article uses the undocumented MFC member function CCmdUI::DoUpdate

Example project with dialog using this technique

You will have used the ON_UPDATE_COMMAND_UI macro in MFC with your various menu commands. This macros is used to implement the message handler for the UPDATE_COMMAND_UI "message" sent by the MFC framework. This message allows you to set the state (enabled/disabled, checked/unchecked etc) of your menu and toolbar items by calling the various OnUpdateXXX functions that you supply.

Quite often, it would be useful to use this same "auto-update" facility with the controls of a dialog box. Unfortunately, MFC does not provide this functionality for you. In this article, I present a dialog class, derived from CDialog, that allows you to use the familiar ON_UPDATE_COMMAND_UI macros with any control on a dialog box.

This approach has the advantage of centralising your dialog controls state logic and is very useful for complicated dialogs where the state of many controls is determined by the state of other controls on the dialog.

The class, CCmdUIDialog, implements the necessary code to call your OnUpdateXXX functions. You simply derive your dialog class from CCmndUIDialog instead of CDialog, and manually add the ON_UPDATE_COMMAND_UI macros to your class.

Class declaration:

#if !defined(AFX_CMDUIDIALOG_H__7D35F4B8_7531_11D1_8FA7_000000000000__INCLUDED_)
#define AFX_CMDUIDIALOG_H__7D35F4B8_7531_11D1_8FA7_000000000000__INCLUDED_

#if _MSC_VER >= 1000
#pragma once
#endif // _MSC_VER >= 1000
// CmdUIDialog.h : header file
// 

/////////////////////////////////////////////////////////////////////////////
// CCmdUIDialog dialog

class CCmdUIDialog : public CDialog
{
// Construction
public:
	CCmdUIDialog(LPCTSTR lpszTemplateName, CWnd* pParentWnd = NULL);
	CCmdUIDialog(UINT nIDTemplate, CWnd* pParentWnd = NULL);
	CCmdUIDialog();
	BOOL ContinueModal();

// Implementation
protected:

	// Generated message map functions
	//{{AFX_MSG(CCmdUIDialog)
	// NOTE: the ClassWizard will add member functions here
	//}}AFX_MSG
	DECLARE_MESSAGE_MAP()
};

//{{AFX_INSERT_LOCATION}}
// Microsoft Developer Studio will insert additional declarations immediately before the previous line.

#endif // !defined(AFX_CMDUIDIALOG_H__7D35F4B8_7531_11D1_8FA7_000000000000__INCLUDED_)

Class Implementation:

// CmdUIDialog.cpp : implementation file
//

#include "stdafx.h"
#include "delme.h"
#include "CmdUIDialog.h"

#ifdef _DEBUG
#define new DEBUG_NEW
#undef THIS_FILE
static char THIS_FILE[] = __FILE__;
#endif

/////////////////////////////////////////////////////////////////////////////
// CCmdUIDialog dialog


CCmdUIDialog::CCmdUIDialog(LPCTSTR lpszTemplateName, CWnd* pParentWnd)
	: CDialog(lpszTemplateName, pParentWnd)
{
}

CCmdUIDialog::CCmdUIDialog(UINT nIDTemplate, CWnd* pParentWnd)
	: CDialog(nIDTemplate, pParentWnd)
{
}

CCmdUIDialog::CCmdUIDialog()
{
}


BOOL CCmdUIDialog::ContinueModal()
{
	// Iterate all child windows and instruct to update themselves
	CWnd* pWndChild=GetWindow(GW_CHILD);
	int iIndex=0;
	while (NULL!=pWndChild)
	{

		CCmdUI state;
		state.m_nID=::GetWindowLong(*pWndChild, GWL_ID);
		state.m_nIndex=iIndex++;
		state.m_pOther=pWndChild;

		// ***CCmdUI::DoUpdate is undocumented MFC***
		state.DoUpdate(this, FALSE);

		pWndChild=pWndChild->GetWindow(GW_HWNDNEXT);
	}

	// Must call the base class
	return CDialog::ContinueModal();
}

BEGIN_MESSAGE_MAP(CCmdUIDialog, CDialog)
	//{{AFX_MSG_MAP(CCmdUIDialog)
		// NOTE: the ClassWizard will add message map macros here
	//}}AFX_MSG_MAP
END_MESSAGE_MAP()

/////////////////////////////////////////////////////////////////////////////
// CCmdUIDialog message handlers



To use the class and update handlers

First, derive your dialog class from CCmdUIDialog instead of CDialog. Next, add update command handlers for each control you require this feature for, using the following technique:

Enter the name of the update function in the protected section of your dialog header file

Each update function has the signature void OnUpdateXXX(CCmdUI* pCmdUI); where XXX might describe the control for this handler. These update functions should be places immediatley after the //}}AFX_MSG comment in your header file. This will ensure that all of the command handlers are grouped together.

Add a ON_UPDATE_COMMAND_UI macro in your dialog source (.cpp) file.

This macro takes the resource ID of the dialog control and the name if the update function to call. For a dialog control called IDC_CHECK1 with a handler function called OnUpdateCheck1 , the macro entry would read

	ON_UPDATE_COMMAND_UI(IDC_CHECK1, OnUpdateCheck1)

This handler should appear between the BEGIN_MESSAGE_MAP and END_MESSAGE_MAP macros and after the //}}AFX_MSG_MAP entry.

Implement the update function

Implement the logic you require in your update function, using the passed CCmdUI pointer to update your dialog control. The passed CCmdUI pointer is based on the dialog control that this habdler is called for.

The attached example application displays a dialog that used the technique described here and also shows how to update more than one control using the same handler function.

Update

Thanks go to Jeff Marino for pointing out this better approach.

Jeff Marino has pointed out an MFC function that handles ON_UPDATE_COMMAND_UI with dialogs and does not require the derived dialog class to call any undocumented MFC stuff. The function is CWnd::UpdateDialogControls.

This just goes to show how large MFC is and that there is a wealth of functionality if only you can find it and how useful your resource is.

To use the UpdateControls function, overload ONE of the PreTranslateMessage or ContinueModal functions like this:

BOOL ::PreTranslateMessage( MSG* pMsg )
{
UpdateDialogControls( this, TRUE );
return CDialog::PreTranslateMessage( pMsg );
}
or
BOOL ::ContinueModal( )
{
UpdateDialogControls( this, TRUE );
return CDialog::ContinueModal( );
}

One should bear in mind that ContinueModal is called about four to five times as often as PreTranslateMessage.