Missing events from ActiveX OCX's -- dotnet interop

Brendan Grant
5/31/2005 4:12:34 PM

I have an old custom written ActiveX control, written in VC++6 that I am
trying to use on a Windows form with C# (and also VB.NET for testing).

I add the control to the toolbox using the standard â€˜add/remove itemsâ€™
option, and everything proceeds fine. As does adding the control to the form.
For the most part I seem to be able to call all of my functions properly
(there are some oddities which are defying debugging for now, however I
expect to track them down just as soon as I have the events working).

The problem currently is the events. No matter how I may add an event
handler to an event on the control, a call never reaches my handler.

What really gets me, is that using the OCX in VB6 works fine, however when I
put an AX wrapper around it for use in .NET, it doesnâ€™t want to talk back.

I also have seen this issues with another custom OCX that I imported via the
same method described above, I can call all of itâ€™s functions, however none
of itâ€™s events are ever fired despite their being triggered.

Brendan Grant
6/1/2005 2:02:08 PM

After spending lots of time in the debugger, looking at the execution of the
OCX, I have found the cause, but not the fix.

The OCX acts as a wrapper to an array of more complicated objects, when each
child object is created, it is given a CWnd pointer to its parent (the OCX).
The CWnd class has a pointer named m_hWnd which refers to the parent/window
of the OCX, this value is null whenever I run the OCX through my C# app. Of
course, when I do so in the VB app, it is non null.

Googling for a fix to this has proven fruitless. Knowing what I know now...
what should I try short of manually passing down a handle from the form as
set at runtime?

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dotnet interop : Missing events from ActiveX OCX's