Excel file corrupted after writing programatically in c#

Question

I am developing c# based application to manipulate excel files. Whenever I write to excel file, the file gets corrupted and nothing appears in it on opening. Also, the next time I am not able to open that file as the application shows the exception. The code goes as below:

 private static Microsoft.Office.Interop.Excel.Workbook mWorkBook;
    private static Microsoft.Office.Interop.Excel.Sheets mWorkSheets;
    private static Microsoft.Office.Interop.Excel.Worksheet mWSheet1;
    private static Microsoft.Office.Interop.Excel.Application oXL;

    public void WriteResultsToSheet() 
    {
        oXL = new Excel.Application();
        oXL.Visible = true;
        oXL.DisplayAlerts = false;
        mWorkBook = oXL.Workbooks.Open(filePath, 0, false, 5, "", "", false, Excel.XlPlatform.xlWindows, "", true, false, 0, true, false, false);
        //Get all the sheets in the workbook
        mWorkSheets = mWorkBook.Worksheets;


        mWSheet1 = (Excel.Worksheet)mWorkBook.Sheets[sheetName.TrimEnd('$')];
        Excel.Range range = mWSheet1.UsedRange;
        int colCount = range.Columns.Count;
        int rowCount = range.Rows.Count;


        for (int index = 1; index <= rowCount; index++)
        {
            try
            {
                Console.WriteLine(dataGridViewScript.Rows[index].Cells[4].Value.ToString());
            }
            catch (NullReferenceException nre)
            {
                if (nre.Message == "Object reference not set to an instance of an object.")
                    break;
            }             
            Console.WriteLine(dataGridViewScript.Rows[index].Cells[5].Value.ToString());
        }


            mWorkBook.SaveAs(filePath, Microsoft.Office.Interop.Excel.XlFileFormat.xlWorkbookNormal,
            Type.Missing, Type.Missing, Type.Missing, Type.Missing, Microsoft.Office.Interop.Excel.XlSaveAsAccessMode.xlExclusive,
            Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing);
        mWorkBook.Close(Type.Missing, Type.Missing, Type.Missing);

        oXL.Quit();
        mWSheet1 = null;
        mWorkBook = null;

        GC.WaitForPendingFinalizers();
        GC.Collect();
        GC.WaitForPendingFinalizers();
        GC.Collect();
        MessageBox.Show("Results exported successfully.");

    }

The exception is as below: COMException was unhandled. Excel cannot open the file because the file format or file extension is not valid. Verify that the file is not corrupt.

Hi! Where's the code that is writing the data to the Excel sheet? — J. D.
– J. D., Commented Aug 1, 2017 at 14:00
Even this code is causing excel to get corrupt. I suspect saving or closing in a wrong way causes this. Please help. — akashagrawal
– akashagrawal, Commented Aug 2, 2017 at 8:35

Devin L. · Accepted Answer · 2017-08-02 23:50:11Z

1

The file is incompatible with Excel because of the file extension. Try changing the file extension to .xls if it was .xlsx and vice versa and then try opening it again.

answered Aug 2, 2017 at 23:50

Devin L.

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