ActiveX plugin causes ASSERT to fail on application exit in VS2008

Question

My MFC application using the "ESRI MapObjects LT2" ActiveX plugin throws an ASSERT at me when closing it. The error occurs in cmdtarg.cpp:

CCmdTarget::~CCmdTarget()
{
#ifndef _AFX_NO_OLE_SUPPORT
    if (m_xDispatch.m_vtbl != 0)
        ((COleDispatchImpl*)&m_xDispatch)->Disconnect();
    ASSERT(m_dwRef <= 1); //<--- Fails because m_dwRef is 3
#endif
    m_pModuleState = NULL;
}

I built the (native C++) application with VC9. When I compile the application with VC6, it behaves nicely.

What could be the reason for this?

Answer 1

The following solved it for me: In the window that contains the control, add an OnDestroy() handler:

void CMyWnd::OnDestroy()
{
    // Apparently we have to disconnect the (ActiveX) Map control manually
    // with this undocumented method.
    COleControlSite* pSite = GetOleControlSite(MY_DIALOG_CONTROL_ID);
    if(NULL != pSite)
    {
        pSite->ExternalDisconnect();
    }

    CWnd::OnDestroy();
}

Answer 2

That looks like a reference count. Could this "target" be referenced by something else, something that's not releasing it?

Answer 3

You can trace the Addref and Release calls defining _ATL_DEBUG_INTERFACES

from http://msdn.microsoft.com/en-us/library/sycfy8ec(VS.80).aspx

_ATL_DEBUG_INTERFACES

Define this macro before including any ATL header files to trace all AddRef and Release calls on your components' interfaces to the output window.

Answer 4

Using _ATL_DEBUG_INTERFACES did not yield any additional output... I defined it on the first line of stdafx.h, directly after #pragma once so I guess this is early enough.

Maybe the reason is how I am using the ActiveX control:
I'm not calling AddRef() or Release() by myself.
The MapObjects Installer comes with sample code with lots of wrapper classes which must have been generated by VC6 or something earlier.
I tried to generate wrapper classes myself with VC9 but there occured errors which I wasn't able to fix. I use the control by letting one of my windows have a member of type CMap1 (derived from CWnd), which is one of those generated wrapper classes. In CMyWnd::OnCreate() I also call CMap1::Create() and that's it, I'm finished: I can add a layer and the control displays a world map.
I have pretty much no idea what the reference-count stuff is about as I have not added or released any references. At least not knowingly...

The control is pretty old: The .OCX file has the year 2000 in its version information.
It's also not officially supported anymore but I don't have any substitue.