How to pass a COleDispatchDriver as an argument for a method expecting a VARIANT

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This article was previously published under Q253501

SUMMARY

Some methods require that you pass a VARIANT that represents an Automation object. With MFC, these objects are typically handled by COleDispatchDriver-derived classes. To pass one of these to a method expecting a VARIANT, you can create a new VARIANT that has the vt member set to VT_DISPATCH and the pdispVal member set to the m_lpDispatch of the COleDispatchDriver class.

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MORE INFORMATION

The following sample uses Microsoft Office Excel as the Automation server. However, the technique that is illustrated can be used with other Microsoft Office applications also.

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Sample code

Excel has several methods that require an object as a parameter. One method is the Worksheet::Add method. The following sample code demonstrates passing a COleDispatchDriver as a parameter to the Worksheet::Add method.

   // Start Excel.
   _Application app;
    
   COleException e;
   if(!app.CreateDispatch("Excel.Application", &e)) {
      char buf[80];
      sprintf(buf, "Error on CreateDispatch(): %ld (%08lx)", e.m_sc, e.m_sc);
      AfxMessageBox(buf, MB_SETFOREGROUND);
      return;
   }
    
   // Make it visible.
   app.SetVisible(TRUE);
    
   // Add a workbook.
   COleVariant covOpt((long)DISP_E_PARAMNOTFOUND, VT_ERROR);
   Workbooks books(app.GetWorkbooks());
   _Workbook book(books.Add(covOpt));
    
   // Get sheets collection of book1.
   Worksheets sheets(book.GetSheets());
    
   // Get a reference to sheet1.
   _Worksheet sheet1(sheets.GetItem(COleVariant((short)1)));
    
   // encapsulate sheet1 object in a VARIANT.
   VARIANT sheet1Var = {0};
   sheet1Var.vt = VT_DISPATCH;
   sheet1Var.pdispVal = sheet1.m_lpDispatch;
   sheet1.m_lpDispatch->AddRef();
    
   // Add a sheet just after sheet1. Excel's Sheets.Add method
   // requires the 'After' parameter to be a sheet object, not
   // a sheet name or index.
   _Worksheet newSheet(sheets.Add(covOpt, sheet1Var, covOpt, covOpt));
    
   AfxMessageBox("All done.", MB_SETFOREGROUND);
    
   // Cleanup.
   VariantClear(&sheet1Var);
   book.SetSaved(TRUE);
   app.Quit();

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REFERENCES

For more information about how to create an MFC Automation client for Microsoft Office applications, click the following article number to view the article in the Microsoft Knowledge Base:

178749 (http://support.microsoft.com/kb/178749/ ) How to create an automation project using MFC and a type library

For more information and for a sample for developing Office solutions, visit the following Microsoft Web sites:

http://support.microsoft.com/ofd (http://support.microsoft.com/ofd)

http://support.microsoft.com/ph/2488 (http://support.microsoft.com/ph/2488)

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