COM Interop - Member not found

Question

I'm try to write a plugin for a 3rd party product. This takes the form of a native C++ DLL, which implements a specified interface from a supplied type library. My plugin is getting loaded successfully, and the methods described by the interface are being called at the expected points, I can write out a log file from my plugin and query a web service, so far so good.

However, for my plugin to query the main program, the Initialize() method passes an IDispatch interface. I'm attempting use this interface with some code like this:

Initialize(LPDISPATCH pDispArchivingControl) {
  LPOLESTR ptName = L"currentVaultId";
  HRESULT hr= pDispArchivingControl->GetIDsOfNames(IID_NULL, &ptName, 1, 
                         LOCALE_USER_DEFAULT, &dispID);
  // add parameters, etc
  hr = pDispArchivingControl->Invoke(dispID, IID_NULL, LOCALE_SYSTEM_DEFAULT, 
                   DISPATCH_METHOD, &dp, pvResult, NULL, NULL);
  // hr = 0x80020003 Member not found.
}

The first section, GetIDsOfNames(), does what I think it should, i.e. putting the names of methods from the program's documentation into ptName gives me different values in dispID - 15, 27, and so on.

The second section, Invoke(), always returns HRESULT 0x80020003 (Member not found).

I found some solutions listed here: HOWTO: Troubleshoot "Member Not Found" 0x80020003 Error. For resolution 1, I tried both DISPATCH_METHOD and DISPATCH_PROPERTYGET as the fourth parameter. Am I right in assuming 2 and 3 cannot apply to me as I am getting the values back in dispID? I'm not sure how to change these either.

I've kinda out of ideas now, and Google is not helping me any further - can anyone suggest what to do next?

UPDATE: This is what one of the methods looks like in oleview. I couldn't find it in the treeview but was able to open it with File > View TypeLib...

method seen in oleview

Doesn't sound much like a method. We can't see dp, it is actually an indexed property? Why are you using late binding when you have a type library? Look at it with Oleview.exe — Hans Passant
@HansPassant I'm using late binding because I don't know what I'm doing :) I'm quite new to C++ and COM. I did also try using an #import with the type library but couldn't work out how to connect the passed interface to it - I tried creating an instance and assigning the interface to it, which compiles but gives "invalid pointer" at runtime. Is #import better for this situation? or something else? — Colin Pickard
The import should create an IArchivingControl interface and maybe even an IArchivingControlPtr ATL smart pointer class if you're lucky. If you've got the smart pointer then just try assigning your IDispatch to it and see if you get a non-null object you can then call against. If you don't have a smart pointer, try calling QueryInterface on the IDispatch with the IID_IArchivingControl and it should create an IArchivingControl interface for you. Don't forget to Release them both when you're done. — Rup
How did we get from "TortoisCount" to "currentVaultId"? They are two very different source control programs. Tortoise is a wrapper for the freeware SVN. I've heard of Vault, that's a commercial SCCS. Are you trying to use late binding to try to ignore fundamental differences between programs? That's a fail whale. — Hans Passant
@HansPassant sorry to be confusing - the code sample was just a couple of example lines to show what I was doing. The screenshot is the real type library. I was using the real function names with GetIDsOfNames(), I was using the documentation supplied with the product for those — Colin Pickard

Colin Pickard Colin Pickard · Accepted Answer · 2012-04-19T14:38:07

The correct answer to this question, given by Hans Passant and Rup in the comments, is not to use late binding, but to #import the type library.

I put this in stdafx.h:

#import "ArchivingControl.tlb" raw_interfaces_only, raw_native_types, named_guids, auto_search

And this in my .cpp file:

ArchivingControl::IArchivingControlPtr JTArchivingControlPtr;
STDMETHODIMP CMyClass::Initialize(LPDISPATCH pDispArchivingControl)
{
   JTArchivingControlPtr = pDispArchivingControl;
   return S_OK;
}
STDMETHODIMP CMyClass::OtherFunction()
{
   BSTR pVaultId;
   JTArchivingControlPtr->get_currentVaultId(&pVaultId);
   return S_OK;
}

And now everything works nicely, plus I have way less code now - Thanks!

COM Interop - Member not found

1 Answers