Question

Using ATL (VS2008) how can I enumerate the available methods available on a given IDispatch interface (IDispatch*)? I need to search for a method with a specific name and, once I have the DISPID, invoke the method (I know the parameters the method takes.) Ideally I would like to do this using smart COM pointers (CComPtr<>).

Is this possible?

Answer 1

You can’t enumerate all the available methods unless the object implements IDispatchEx.

However, if you know the name of the method you want to call, you can use GetIDsOfNames to map the name to the proper DISPID.

HRESULT hr;
CComPtr<IDispatch> dispatch;
DISPID dispid;
WCHAR *member = "YOUR-FUNCTION-NAME-HERE";
DISPPARAMS* dispparams;

// Get your pointer to the IDispatch interface on the object here.  Also setup your params in dispparams.

hr = dispatch->GetIDsOfNames(IID_NULL, &member, 1, LOCALE_SYSTEM_DEFAULT, &dispid);
if (SUCCEEDED(hr)) {
  hr = dispatch->Invoke(1, IID_NULL, LOCALE_USER_DEFAULT, DISPATCH_METHOD, dispparams, &varResult, NULL, NULL);
}

Edit: For completeness, I suspect there is a way to interrogate the ITypeInfo2 interface (assuming there is a type library for the object) that you get from IDispatch::GetTypeInfo for a list of methods, but I’ve not done it. See the other answer.