Re: Crash during "scalar deleting destructor" with IDocHostUIHandler!

"Chris Shearer Cooper" <>
Thu, 14 Dec 2006 19:57:35 -0700
Here's something I don't understand though ...

/* virtual */ HRESULT CHtmlDlg::CDocHostUIHandler::GetExternal(
            /* [out] */ IDispatch __RPC_FAR *__RPC_FAR *ppDispatch)
 TRACE(L"CDocHostUIHandler::GetExternal(ppDispatch=%p)\n", ppDispatch);

 External* pExt = new External;
 *ppDispatch = pExt->GetIDispatch(FALSE);
 return S_OK;

If I specify TRUE in the GetIDispatch() call, my 'External' object never
gets deleted. If I specify FALSE, it works fine.

Is there an implicit AddRef() going on in the CCmdTarget constructor or


"Igor Tandetnik" <> wrote in message

"Chris Shearer Cooper" <> wrote in message

In my MFC C++ app, I'm creating a browser window inside a dialog, and
I want to have it be able to communicate with my application. It
seems like the way to do this, is to create a class that implements
IDocHostUIHandler, pass it into the ICustomDoc::SetUIHandler(), and
then implement a dispatch class (one that implements IDispatch) which
I return when the HTML control calls my

You don't need to use ICustomDoc when hosting WebBrowser control. See
Driller sample for details.

However, now I have a class that derives from CCmdTarget and calls
EnableAutomation in its constructor, so it should be a happy
IDispatch kind of guy. When my IDocHostUIHandler::GetExternal is
called, I 'new' up one of those, call its InternalAddRef(), and then
store its address into the ppDispatch passed to me in the GetExternal
call. I can step through that with the debugger, but as soon as that
function returns, I get a C0000005 exception.

  *ppDispatch = (IDispatch*)pExt;

The exception is due to this cast. You need to use
CCmdTarget::GetIDispatch to obtain IDispatch* pointer.
With best wishes,
   Igor Tandetnik

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necessarily a good idea. It is hard to be sure where they are going to
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