ASSERT in ~CCmdTarget after Drag&Drop between MFC and C#

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whagedorn - 21 Sep 2007 07:29 GMT

Hi,

I have written a small test application, where I integrated a c#
forms-window in a mfc-application via COM Interop.
Everthing is running very well, but if I use Drag&Drop from the MFC-part to
the C# window I got a debug ASSERT
in the destructor of the CCmdTaget-Class, which is the baseclass of the
using COleDataSource-object.

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

It seems, that the garbage collector will not release this object after
dropping it.
I try to realease it manually, but without any success.

Any ideas or suggestions are appreciated.

Thanks,
Wilfried

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G Himangi - 21 Sep 2007 09:38 GMT

Yes, the garbage collector runs at random times. You can explicitly release
the COMobject in C# by calling Marshal.ReleaseComObject.

However, the problem may also be that you are using a delete on the
COleDataSource-object, instead of that, you should use InternalRelease.

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> Hi,
>
[quoted text clipped - 25 lines]
> Thanks,
> Wilfried

Reply to this Message

whagedorn - 21 Sep 2007 10:03 GMT

The main problem is, that I don't have any access to the
COleDataSource-object, which is encapsulate
in a DragEventsArg-object on the c# side. It is further wrapped from the
interop layer ( e.g. COleConvert ), so there is no chance to release it from
the drop target.
I have tried to call GC.Collect() after setting the DragEventsArg-object to
null, but without any success.

> Yes, the garbage collector runs at random times. You can explicitly
> release the COMobject in C# by calling Marshal.ReleaseComObject.
[quoted text clipped - 40 lines]
>> Thanks,
>> Wilfried

Reply to this Message

Christian Fröschlin - 21 Sep 2007 14:54 GMT

> I have tried to call GC.Collect() after setting the
> DragEventsArg-object to null, but without any success.

That wouldn't help much unless you also
called GC.WaitForPendingFinalizers().

Reply to this Message

whagedorn - 24 Sep 2007 09:07 GMT

Hello Christian ,

I've tried several things to release the COM-Object, but I believe the main
problem is,
that I cannot get access to the wrapped interface itself.

Here's a c# code fragment of my project. The drop source is a
MFC-Application which
creates a COleDataSource object on the stack and calls then its DoDragDrop()
method.

void list_DragDrop(object sender, DragEventArgs e)
{
if (e.Data.GetDataPresent(JVSDragDropFormat))
{
e.Data.SetData(JVSDragDropFormat, null);

// object data = e.Data.GetData(JVSDragDropFormat);
// data = null;

GC.Collect();
GC.WaitForPendingFinalizers();
}
}
Any ideas ?

Wilfried

>> I have tried to call GC.Collect() after setting the DragEventsArg-object
>> to null, but without any success.
>
> That wouldn't help much unless you also
> called GC.WaitForPendingFinalizers().

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ASSERT in ~CCmdTarget after Drag&Drop between MFC and C#

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