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;
}