Missing WM_INITDIALOG for dialog window in DLL

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C++

Hello

I have been trying to create a DLL in C++ using Visual Studio 2012. The aim is to convert the MFPLayer sample which uses the Microsoft Media Foundation to play a video file into a DLL that does the same thing. The MFPlayer samples is a win32 application and it compiles and runs.

The sample can be found in MFSamples.zip at :
http://archive.msdn.microsoft.com/mediafoundation

Previously I successfully created a Dll version of the BasicPlayback sample which also plays videos. I managed to call the dll functions from a c# application. I use the same procedure for this new dll.

However, MFPlayer sample doesn't work. The dll calls the following function

BOOL MainDialog::ShowDialog(HINSTANCE hinst)
{
    // Show the dialog. Pass a pointer to ourselves as the LPARAM
    INT_PTR ret = DialogBoxParam(
        hinst, 
        MAKEINTRESOURCE(m_nID), 
        NULL, 
        DialogProc, 
        (LPARAM)this
        );

    if (ret == 0 || ret == -1)
    {
        MessageBox( NULL, L"Could not create dialog", L"Error", MB_OK | MB_ICONERROR );
        return FALSE;
    }

    return (IDOK == ret);
}

After calling DialogBoxParam the DialogProc is called to handle several messages but the WM_INITDIALOG message is never sent.

Here's some of the other relevant code....

BOOL APIENTRY DllMain (HINSTANCE hInstance, DWORD reason, LPVOID reserved)
{
	g_hInstance = hInstance;
	return TRUE;
}
extern "C"
{
__declspec(dllexport) int PlayMovie()
{
    HeapSetInformation(NULL, HeapEnableTerminationOnCorruption, NULL, 0);

    // Initialize the COM library.
    HRESULT hr = CoInitializeEx(NULL, COINIT_APARTMENTTHREADED | COINIT_DISABLE_OLE1DDE);

    if (FAILED(hr))
    {
        MessageBox(NULL, L"CoInitialize failed.", NULL, MB_ICONSTOP);
        return 0;
    }

    // Initialize the common control library.
    INITCOMMONCONTROLSEX icc;
    icc.dwSize = sizeof(icc);
    icc.dwICC = ICC_STANDARD_CLASSES | ICC_BAR_CLASSES;
    if (!InitCommonControlsEx(&icc))
    {
        MessageBox(NULL, L"InitCommonControlsEx failed.", NULL, MB_ICONSTOP);
        CoUninitialize();
        return 0;
    }

    // Initialize our custom slider class.
    hr = Slider_Init();
    if (FAILED(hr))
    {
        MessageBox(NULL, L"Slider_Init failed.", NULL, MB_ICONSTOP);
        CoUninitialize();
        return 0;
    }

    // Create and show the dialog.
    MainDialog *pDlg = new (std::nothrow) MainDialog();
    if (pDlg == NULL)
    {
        MessageBox(NULL, L"Out of memory.", NULL, MB_ICONSTOP);
    }
    else
    {
        pDlg->ShowDialog(g_hInstance);

        delete pDlg;
    }

    CoUninitialize();
    return 0;
}

You will notice that I capture the HINSTANCE sent to DllMain and use this for the API calls. Play PlayMovie function is called from C#.

I have to say that I am completely new to windows programming and I might be missing something simple. However, I was hoping someone could give me some clues as to where to look.


In summary, the dll compiles. It is called from a c# application. It runs without error but the WM_INITDIALOG message is never sent to DialogProc. Any ideas..

Here's some additional information...

I put a breakpoint in DialogProc and get the following messages:

48 = WM_SETFONT 
85 = WM_NOTIFYFORMAT 
297 = WM_QUERYUISTATE  
144 = Not Defined
2 = WM_DESTROY 
130 = WM_NCDESTROY 

INT_PTR CALLBACK MainDialog::DialogProc(HWND hDlg, UINT msg, WPARAM wParam, LPARAM lParam)
{
    MainDialog *pDlg = 0;  // Pointer to the dialog class that manages the dialog 

    LRESULT lresult = 0;

    if (msg == WM_INITDIALOG)
    {
        // Get the pointer to the dialog object and store it in 
        // the window's user data

        SetWindowLongPtr(hDlg, DWLP_USER, (LONG_PTR)lParam);

        pDlg = (MainDialog*)lParam;
        if (pDlg)
        {
            pDlg->m_hDlg = hDlg;
            HRESULT hr = pDlg->OnInitDialog();
            if (FAILED(hr))
            {
                pDlg->EndDialog(0);
            }
        }
        return FALSE;
    }

    // Get the dialog object from the window's user data
    pDlg = (MainDialog*)(DWORD_PTR) GetWindowLongPtr(hDlg, DWLP_USER);

    if (pDlg != NULL)
    {
        switch (msg)
        {
        case WM_COMMAND:
            switch (LOWORD(wParam))
            {
            case IDOK:
            case IDCANCEL:
                pDlg->EndDialog(LOWORD(wParam));
                return TRUE;

            default:
                return pDlg->OnCommand((HWND)lParam, LOWORD(wParam), HIWORD(wParam));
            }
            break;

        case WM_NOTIFY:
            lresult = pDlg->OnNotify((NMHDR*)lParam);

            // The LRESULT from WM_NOTIFY can be meaningful. Store the result in DWLP_MSGRESULT.
            SetWindowLongPtr(hDlg, DWLP_MSGRESULT, (LONG_PTR)lresult);
            return TRUE;

        default:
            return pDlg->OnReceiveMsg(msg, wParam, lParam);
        }
    }
    else
    {
        return FALSE;
    }
}

The DialogBoxParam returns -1 but a call to GetLastError() gives 0 signifying that there has not been an error.

Many thanks....