ATL COM EXE Server with MFC support

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Introduction

This article will explain implementing an ATL COM EXE server with MFC support. As an example, we create an ATL COM EXE server that can create an MFC child window and an ATL child window in the client side’s parent window.

Background

In a recent project, we are trying to add MFC Support to an ATL EXE server. We want to create both MFC window using CWnd derived class and ATL window using CWindow in our server. There was an article in MSDN about this :'Q 173974 : HOWTO: Add MFC Support to an ATL Project'. And this is the main reference from which we created our example application.

Using the code

The code consists of two Microsoft Visual C++ 6.0 projects:

• ATLMFCCOMClient - Client side implementation. This is a simple SDI application.
• ATLMFCCOMServer - Server side implementation.

These projects support both non-Unicode and Unicode compilation.

Server side implementation

This project was first created using ATL COM Wizard, and then modified to support MFC according MSDN's article Q 173974. However, this is not enough; there are other three modifications we should add:

1. Add AtlAxWinInit() in CMyApp::InitInstance().

   This will allow us create ATL window correctly. See Figure 1.

2. Add _Module.StartMonitor() in CMyApp::InitInstance().

   2 and 3 allow the EXE server exit correctly when the client exits. See Figure 1.

3. Add theApp.PostThreadMessage( WM_QUIT, 0, 0) in CExeModule::MonitorShutdown().

   See Figure 2.

BOOL CMyApp::InitInstance()
     {
        // Initialize OLE libraries

        if (!AfxOleInit())
        {
           AfxMessageBox(_T("OLE Initialization Failed!"));
           return FALSE;
        }
       AtlAxWinInit();

        // Initialize the ATL Module

        _Module.Init(ObjectMap,m_hInstance);
     #ifdef _AFXDLL
        Enable3dControls(); // Call this when using MFC in a shared DLL

     #else
        Enable3dControlsStatic(); // Call this when linking

                                  // to MFC statically

     #endif
        // Update the System Registry

        COleObjectFactory::UpdateRegistryAll(); // MFC Classes

        VERIFY(SUCCEEDED(_Module.RegisterServer(TRUE))); // ATL Classes

        // Create the dialog box or other stuff here

        // Register OLE Class Factories

        // MFC ones are for multiple as specified

        // by the IMPLEMENT_OLECREATE() macro

        COleObjectFactory::RegisterAll();
        // ATL ones specifically register with REGCLS_MULTIPLEUSE

        VERIFY(SUCCEEDED(_Module.RegisterClassObjects(CLSCTX_LOCAL_SERVER, 
             REGCLS_MULTIPLEUSE)));

        _Module.StartMonitor();
        // Parse the command line to see if launched as OLE server

        if (RunEmbedded() || RunAutomated())
        {
           // Application was run with /Embedding or /Automation.

           // Don't show the main window in this case.

           return TRUE;
        }

        return FALSE; // Nothing to do, so exit.

     }

Figure 1

//Monitors the shutdown event

void CExeModule::MonitorShutdown()
{
    while (1)
    {
        WaitForSingleObject(hEventShutdown, INFINITE);
        DWORD dwWait=0;
        do
        {
            bActivity = false;
            dwWait = WaitForSingleObject(hEventShutdown, dwTimeOut);
        } while (dwWait == WAIT_OBJECT_0);
        // timed out

        if (!bActivity && m_nLockCnt == 0) // if no activity let's really bail

        {
#if _WIN32_WINNT >= 0x0400 & defined(_ATL_FREE_THREADED)
            CoSuspendClassObjects();
            if (!bActivity && m_nLockCnt == 0)
#endif
                break;
        }
    }
    CloseHandle(hEventShutdown);
    PostThreadMessage(dwThreadID, WM_QUIT, 0, 0);
    theApp.PostThreadMessage( WM_QUIT, 0, 0);

}

Figure 2

We created two COM objects: ATLWindowObject and MFCWindowObject.

ATLWindowObject has two interfaces: CreateATLWindow and Update.

MFCWindowObject has two interfaces: CreateMFCWindow and Update.

Both Update() interfaces are used to refresh the window when the client side parent window needs to be refreshed. See Client side implementation section.

We also created two window classes :CMFCWnd derived from CWnd and CATLWnd derived from CWindow. CMFCWnd will be created by MFCWindowObject while CATLWnd will be created by ATLWindowObject.

CMFCWnd is easy, but CATLWnd needs adding a message map manually, See Figure 3.

class CATLWnd : public CWindowImpl<CATLWND, CWindow>
{
public:
    DECLARE_WND_CLASS(_T("ATL Window Class"))
    CATLWnd() { m_hbrBkgnd = CreateSolidBrush(RGB(0,0,255)); }
    ~CATLWnd() { DeleteObject ( m_hbrBkgnd ); }
 
    BEGIN_MSG_MAP(CATLWnd)
        MESSAGE_HANDLER(WM_PAINT, OnPaint)
    END_MSG_MAP()

    LRESULT OnPaint(UINT uMsg, WPARAM wParam, LPARAM lParam, BOOL& bHandled)
    {
        RECT rcClient;
        PAINTSTRUCT ps;
        BeginPaint(&ps);
        HDC  dc = GetDC();
        GetClientRect ( &rcClient );
        FillRect ( dc, &rcClient, m_hbrBkgnd );
        TextOut(dc,2,10,_T("ATL Window"),10);
        EndPaint(&ps);
        return 0;    
    }
protected:
    HBRUSH m_hbrBkgnd;
};

Figure 3

Client side implementation

The function OnMfcWindow will be called, when user select “Create MFC Window” menu. MFCWindowObject will first be instantiated, and its interface CreateMFCWindow will be called to create a MFC window.

Likely, the function OnATLWindow will be called, when user select “Create ATLWindow” menu. ATLWindowObject will first be instantiated, and its interface CreateATLWindow will be called to create an ATL window. See Figure 4.

Note that both windows are the child windows of CATLMFCCOMClientView

void CATLMFCCOMClientView::OnMfcWindow() 
{
    if(m_pMFCWindowObject) return;
    HRESULT hResult = S_OK;          
    hResult = CoCreateInstance(CLSID_MFCWindowObject,
         NULL,CLSCTX_LOCAL_SERVER,IID_IMFCWindowObject,
         (LPVOID*)&m_pMFCWindowObject);
    m_pMFCWindowObject->CreateMFCWindow((long)m_hWnd);
}

void CATLMFCCOMClientView::OnAtlWindow() 
{
    if(m_pATLWindowObject) return;
    HRESULT hResult = S_OK;          
    hResult = CoCreateInstance(CLSID_ATLWindowObject,
        NULL,CLSCTX_LOCAL_SERVER,IID_IATLWindowObject,
        (LPVOID*)&m_pATLWindowObject);
    m_pATLWindowObject->CreateATLWindow((long)m_hWnd);
}

Figure 4

In server side implementation section, we mentioned that both the COM objects: ATLWindowObject and MFCWindowObject provided interface Update. This interface is used in CATLMFCCOMClientView::OnDraw to avoid window refresh issue, See Figure 5.

void CATLMFCCOMClientView::OnDraw(CDC* pDC)
{
    CATLMFCCOMClientDoc* pDoc = GetDocument();
    ASSERT_VALID(pDoc);
    if(m_pMFCWindowObject)
        m_pMFCWindowObject->Update();
    if(m_pATLWindowObject)
        m_pATLWindowObject->Update();
}

Figure 5