Multiple Top Level Windows

Download demo project - 7 Kb

Download source files - 18 Kb

Introduction

MFC, out of the box, supports three interface models, MDI, SDI, and dialog based. What it doesn't have is support for MTLW (ok, so MS probably has a different acronym for it, but what I mean is Multiple Top Level Windows). This is the model popularized by those web browsers we all know and love, Netscape Navigator and Internet Explorer.

Problem

The main problem with MTLW and MFC is the main window (aka CWinApp::m_pMainWnd).

1. MFC expects there to be one.
2. MFC will close the application as soon as the main window is closed.

Solution

So what we need is a way to keep CWinApp::m_pMainWnd pointed at a valid TLW and switch it from one window to another as needed to make sure that the app doesn't shut down except when the last TLW is closed.

Two classes will help you do this:

• CMultiTopApp - should be used as the base class for your app object.
• CTopLevelFrame - should be used as the base class for CMainFrame.

Derive from these classes and wire up the message maps properly, and that's it. You're app now supports MTLW. Of course you need to have ways of creating new TLWs and probably you want to have a command to close all the windows and shut down your app, so the demo project includes those functions.

First, a handler for the "New Window" menu item creates new TLWs.

void CMultiTopSample::OnFileNewwindow() 
{
	CMainFrame* pFrame = new CMainFrame;

	// create and load the frame with its resources

	pFrame->LoadFrame(IDR_MAINFRAME,
		WS_OVERLAPPEDWINDOW | FWS_ADDTOTITLE, NULL,
		NULL);

	// The one and only window has been initialized,
	// so show and update it.

	pFrame->ShowWindow(SW_SHOW);
	pFrame->UpdateWindow();
}

Second, unless you want your users to have to close each window individually, you may want to have an "Exit" menu item which does the following:

void CMultiTopSample::OnAppExit() 
{
	CloseAllFrames() ;
}

Is this easy, or what!

How it works (briefly), and a BONUS member function:

CMultiTopApp has an STL list for keeping track of TLWs...

list< CTopLevelFrame* > m_listMainFrames ;

... and a few functions for manipulating them:

void AddFrame( CTopLevelFrame* pFrame ) ;         // Adds a TLW to list

void KillFrame( CTopLevelFrame* pFrame ) ;        // Removes TLW from list

void ReplaceMainFrame( CTopLevelFrame* pFrame ) ; // Makes a differnt TLW the
                                               // MFC main window if possible

Plus a special bonus function. I use this to do print preview in YATLW and disable all the regular TLWs while I do so.

void EnableFrames( BOOL bEnable ); // Enables/Disables all TLWs in list

CTopLevelFrame uses the CMultiTopApp member functions in response to window creation and destruction messages.

MESSAGE	Handler	Action
WM_CREATE	OnCreate()	calls AddFrame() after default processing
WM_CLOSE	OnClose()	calls ReplaceMainFrame() before default processing
WM_DESTROY	OnDestroy()	calls KillFrame() after default processing