Excel COM Object Cast Error

Question

I'm trying to avoid "double dot" notation in my code (see How do I properly clean up Excel interop objects?). However, I get an error when I try to change the following code

Excel.Workbook oWB;
...
oWB.Sheets[oWB.Sheets.Count].Delete();
oWB.Sheets[oWB.Sheets.Count].Delete();
oWB.Sheets[oWB.Sheets.Count].Delete();

to this

Excel.Sheets oS;
oS = oWB.Sheets;
//error occurs in the following line
oS = oWB.Sheets[oS.Count];
oS.Delete();
oS.Delete();
os.Delete();

The error is 'Unable to cast COM object of type 'System.__ComObject' to interface type 'Microsoft.Office.Interop.Excel.Sheets'. This operation failed because the QueryInterface call on the COM component for the interface with IID '{000208D7-0000-0000-C000-000000000046}' failed due to the following error: No such interface supported (Exception from HRESULT: 0x80004002 (E_NOINTERFACE)).'

Any help is appreciated.

Seb · Accepted Answer · 2014-09-29 14:36:17Z

1

You have to declare a new variable of type Sheet. oS is of type Sheets, while oS.Sheets[os.Count] is of type Sheet (without final 's'). As these are unrelated type from the runtime point of view, you must declare an intermediate variable with appropriate type Sheet.

answered Sep 29, 2014 at 14:36

Seb

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