Obtaining the Excel.Application IDispatch* within a dll that's been loaded into Excel

Question

Does anyone know how to get hold of the Excel.Application IDispatch* pointer associated with an excel process into which an dll has been loaded?

A key thing here is that the process is excel.exe, and the pointer I need must belong to that process. Using the Running Object Table will not fly since Excel only registers its first instance with that.

I'm hoping there is some low-level COM trickery, but I'm not an expert in that field.

Answer 1

EDITED II Code is under the WTFPL license version 2.

EDITED: Add PID parameter to allow filtering when several Excel processes are currently running, as per comment suggestion from @EricBrown.

I managed to get a working IDispatch* to an Excel "Application" object without using the ROT. The trick is to use MSAA. My code works as a stand alone console application, but I think that if the code is executed in an Excel process, via DLL Injection, it MAY works fine. You may have to be in a dedicated thread. Let me know if you want me to push the expriment to the DLL injection level.

Tested OK on Window7 64b, with a UNICODE builds (32 bits and 64 bits). Excel version 2010 64 bits (version "14")

I get the IDispatch via the "application" property from an "Worksheet" object. Consequence: there must be an opened worksheet. In order to find the good MSSA Window, I need the class name of the Top Level Excel Frame Window. In Excel 2010, it's "XLMAIN". The class name for worksheets is "EXCEL7" and that seems to be a "standard".

I was not able to directly get a working IDispatch* from the main Excel Window, but have not tried very hard. That may involve #import with a automation DLL from Excel, in order to QueryInterface the IDispatch that MSAA gives for the main Window (that IDispatch is NOT for an Application object)

#include <atlbase.h>

#pragma comment( lib, "Oleacc.lib" )

HRESULT GetExcelAppDispatch( CComPtr<IDispatch> & spIDispatchExcelApp, DWORD dwExcelPID ) {

   struct ew {
      struct ep {
         _TCHAR* pszClassName;
         DWORD dwPID;
         HWND hWnd;
      };
      static BOOL CALLBACK ewp( HWND hWnd, LPARAM lParam ) {
         TCHAR szClassName[ 64 ];
         if ( GetClassName( hWnd, szClassName, 64 ) ) {
            ep* pep = reinterpret_cast<ep*>( lParam );
            if ( _tcscmp( szClassName, pep->pszClassName ) == 0 ) {
               if ( pep->dwPID == 0 ) {
                  pep->hWnd = hWnd;
                  return FALSE;
               } else {
                  DWORD dwPID;
                  if ( GetWindowThreadProcessId( hWnd, &dwPID ) ) {
                     if ( dwPID == pep->dwPID ) {
                        pep->hWnd = hWnd;
                        return FALSE;
                     }
                  }
               }
            }
         }
         return TRUE;
      }
   };

   ew::ep ep;

   ep.pszClassName = _TEXT( "XLMAIN" );
   ep.dwPID = dwExcelPID;
   ep.hWnd = NULL;
   EnumWindows( ew::ewp, reinterpret_cast<LPARAM>( &ep ) );
   HWND hWndExcel = ep.hWnd;
   if ( ep.hWnd == NULL ) {
      printf( "Can't Find Main Excel Window with EnumWindows\n" );
      return -1;
   }

   ep.pszClassName = _TEXT( "EXCEL7" );
   ep.dwPID = 0;
   ep.hWnd = NULL;
   EnumChildWindows( hWndExcel, ew::ewp, reinterpret_cast<LPARAM>( &ep ) );
   HWND hWndWorkSheet = ep.hWnd;
   if ( hWndWorkSheet == NULL ) {
      printf( "Can't Find a WorkSheet with EnumChildWindows\n" );
      return -1;
   }

   CComPtr<IDispatch> spIDispatchWorkSheet;
   HRESULT hr = AccessibleObjectFromWindow( hWndWorkSheet, OBJID_NATIVEOM, IID_IDispatch,
                                            reinterpret_cast<void**>( &spIDispatchWorkSheet ) );
   if ( FAILED( hr ) || ( spIDispatchWorkSheet == 0 ) ) {
      printf( "AccessibleObjectFromWindow Failed\n" );
      return hr;
   }
   CComVariant vExcelApp;
   hr = spIDispatchWorkSheet.GetPropertyByName( CComBSTR( "Application" ), &vExcelApp );
   if ( SUCCEEDED( hr ) && ( vExcelApp.vt == VT_DISPATCH ) ) {
      spIDispatchExcelApp = vExcelApp.pdispVal;
      return S_OK;
   }
   return hr;

}
int _tmain(int argc, _TCHAR* argv[])
{

   DWORD dwExcelPID = 0;
   if ( argc > 1 ) dwExcelPID = _ttol( argv[ 1 ] );

   HRESULT hr = CoInitialize( NULL );
   bool bCoUnInitializeTodo = false;
   if ( SUCCEEDED( hr ) ) {
      bCoUnInitializeTodo = true;
      CComPtr<IDispatch> spDispatchExcelApp;
      hr = GetExcelAppDispatch( spDispatchExcelApp, dwExcelPID );
      if ( SUCCEEDED( hr ) && spDispatchExcelApp ) {
         CComVariant vExcelVer;
         hr = spDispatchExcelApp.GetPropertyByName( CComBSTR( "Version" ), &vExcelVer );
         if ( SUCCEEDED( hr ) && ( vExcelVer.vt == VT_BSTR ) ) {
            wprintf( L"Excel Version is %s\n", vExcelVer.bstrVal );
         }
      }
   }
   if ( bCoUnInitializeTodo ) CoUninitialize();
   return 0;
}

Answer 2

You should be able to find out how to do this by reviewing the code in ExcelDNA. This project contains code that hooks back into Excel from the extension library. The code is likely to be more elaborate that you need, but will implement the reference you require.

Answer 3

This is how I do it: (acknowledge @manuell). dispatch_wrapper is a class, here is the constructor to set m_disp_application:

dispatch_wrapper(void)
{
    DWORD target_process_id = ::GetProcessId(::GetCurrentProcess());

    if (getProcessName() == "excel.exe"){
        HWND hwnd = ::FindWindowEx(0, 0, "XLMAIN", NULL);
        while (hwnd){
            DWORD process_id;
            ::GetWindowThreadProcessId(hwnd, &process_id);
            if (process_id == target_process_id){
                HWND hwnd_desk = ::FindWindowEx(hwnd, 0, "XLDESK", NULL);
                HWND hwnd_7 = ::FindWindowEx(hwnd_desk, 0, "EXCEL7", NULL);
                IDispatch* p = nullptr;
                if (SUCCEEDED(::AccessibleObjectFromWindow(hwnd_7, OBJID_NATIVEOM, IID_IDispatch, (void**)&p))){
                    LPOLESTR name[1] = {L"Application"};
                    DISPID dispid;
                    if (SUCCEEDED(p->GetIDsOfNames(IID_NULL, name, 1U, LOCALE_SYSTEM_DEFAULT, &dispid))){
                        CComVariant v;
                        DISPPARAMS dp;
                        ::memset(&dp, NULL, sizeof(DISPPARAMS));
                        EXCEPINFO ei;
                        ::memset(&ei, NULL, sizeof(EXCEPINFO));
                        if (SUCCEEDED(p->Invoke(dispid, IID_NULL, LOCALE_SYSTEM_DEFAULT, DISPATCH_PROPERTYGET, &dp, &v, &ei, NULL))){
                            if (v.vt == VT_DISPATCH){
                                m_disp_application = v.pdispVal;
                                m_disp_application->AddRef();
                                return;
                            }
                        }
                    }
                }
            }
            hwnd = ::FindWindowEx(0, hwnd, "XLMAIN", NULL);
        }
    }
    m_disp_application = nullptr;
}

getProcessName() returns lower case.

Answer 4

Because Office applications register their documents in the ROT, you can attach to instances beside the first one (which is already in the ROT) by getting IDispatch for documents in the ROT, then you can use document.Application.hwnd (this is VBA, you need to translate to IDispatch::GetIDsOfNames and IDispatch::Invoke with DISPATCH_PROPERTYGET) to get the window handles of all Excel instances.

Now you have a mapping between IDispatch and Windows handles of all Excel instances, it is time to find your own Excel instance. You can call GetWindowThreadProcessId on the window handles to get the process ids, then compare to your own process id returned by GetCurrentProcessId to see which excel window belongs to your current process, and look up in the HWND to IDispatch mapping to find your current Excel application's IDispatch interface.