Called by the framework when Excel opens the XLL
                virtual void OnXllOpen( );  | 
            
This function is called whenever a user loads the add-in, whether using the Excel Tools - Add-ins dialog or directly, using the File - Open menu option.
This is a good time to do any initialization that needs to precede any use of your add-in functions, so long as the initialization cannot fail.
The default implementation of this function does nothing.
 Note: | 
          
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           This method is deprecated. Use OnXllOpenEx instead.  | 
          
Header: xllplus.h
CXllApp Class | CXllApp Methods | CXllApp::OnXllOpenEx() | CXllApp::OnXllClose()