On Tue, Oct 12, 2010 at 6:29 PM, Greg Keogh <g...@mira.net> wrote:
> Folks, we had a shocking problem today where C# code was listening for
> events from a VB6 component. The COM classes exposed by the VB6 app are
> nested and a bit complicated to describe, but a nested class which exposed
> events was randomly producing the dreaded “COM object that has been
> separated from its underlying RCW cannot be used”. The random nature of the
> problem hinted that it was garbage or dispose related. After a bit of
> suffering I found the following solution (feature and Cursor are COM
> classes):
>
> GCHandle cursorHandle = GCHandle.Alloc(feature.Cursor, GCHandleType.Normal);
>
> feature.Cursor.NotifyMoveNext += event handler;
>
> feature.ShowModalDialog(...);
>
> if (cursorHandle.IsAllocated)
>
> {
>
> cursorHandle.Free();
>
> feature.Cursor.NotifyMoveNext -= event handler;
>
> }
>
> It used to randomly die on the removal of the event handler. The Alloc and
> Free seem to have totally solved the problem.
>
> This code seems a bit obscure and arcane, so I was wondering if anyone had
> comments on it. Perhaps there are better ways.
>
> Greg
It looks to me simply like you need to hold the reference to
feature.Cursor until you remove the event handler. To test this,
simply change your code to
var cursorHolder = feature.Cursor;
feature.Cursor.NotifyMoveNext += event handler;
feature.ShowModalDialog(...);
feature.Cursor.NotifyMoveNext -= event handler;
GC.KeepAlive(cursorHolder);
Of course if other things are afoot and sometimes
cursorHandle.IsAllocated is False, then the above may not be what you
need.
--
Regards,
Mark Hurd, B.Sc.(Ma.)(Hons.)
