Called by the framework when a workbook is activated
[C++]
virtual void OnWorkbookActivate(
   LPDISPATCH dispWorkbook
);
Pointer to dispatch interface of type Excel.Workbook.
This function is called whenever a workbook is activated,
            just after the corresponding OnWorkbookDeactivate event
            for the previously active workbook. Note that it will only be called if event-sinking is switched on 
            (using CXllApp::SetSinkEvents()). You can override the method in your application class
            to react to the event.
            The default method does nothing.
Header: xllplus.h
CXllApp Class 
					  | CXllApp Methods			 
					  | CXllApp::OnWorkbookDeactivate()			 
					  | CXllApp::OnSheetActivate()			 
					  | CXllApp::OnSheetDeactivate()