C++ problem accessing ms office interop API from background thread

Question

MS Office interop API working when called within the class containing Addin OnConnection method. But when i call the same API from another thread, it fails with some unknown exception.

Read in few forum pages that Office automation is Single-threaded.

Any way to override this behaviour? Few people in few forums mentioned about using IMessageFilter, but i can't figure it out about using it in C++.

Please guide. Here is some sample code.

CComQIPtr<Word::_Application> pWordApp;  
CComQIPtr<Word::Windows> spWindows;  
  
DWORD WINAPI fn(LPVOID lpParam)  
{  
          pWordApp->get_Windows(&spWindows);  //////// not working, some exception is raised  
}  
  
class ATL_NO_VTABLE CConnect :  
{  
public:  
STDMETHOD(OnConnection)(LPDISPATCH Application, ext_ConnectMode ConnectMode, LPDISPATCH AddInInst, SAFEARRAY** custom)  
{  
pWordApp = Application;  
  
pWordApp->get_Windows(&spWindows); ////// working  
  
CreateThread(NULL, 0, fn, NULL, 0, NULL);  
}  
  
}  

Answer 1

Try calling OleInitialize( ) at the beginning of fn.

Or call CoInitializeEx(NULL, COINIT_APARTMENTTHREADED).