Excel 2010 COM Object Links Not Released

Question

The following code sample worked fine in Excel 2007, but when I installed Excel 2010 (32 bit), it would leave the excel.exe process open if I did not add GC.Collect (). My simple question is: am I doing something wrong? It seems to me that I release everything that I use.

    public override void Update()
    {

        StatusBox.AddStatus("Opening File " + ImportPath);

        Microsoft.Office.Interop.Excel.Application app = new Microsoft.Office.Interop.Excel.Application();
        Microsoft.Office.Interop.Excel.Workbook wb = app.Workbooks.Open(ImportPath, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing);
        Microsoft.Office.Interop.Excel.Worksheet ws = (Microsoft.Office.Interop.Excel.Worksheet)wb.Sheets[1];

        Range rng = ws.Cells.SpecialCells(XlCellType.xlCellTypeLastCell, Type.Missing);

        int LastRow = rng.Row;

        StatusBox.AddStatus(LastRow.ToString() + " Rows Found in File");


        StatusBox.AddStatus("Closing File " + ImportPath);

        System.Runtime.InteropServices.Marshal.ReleaseComObject(rng);
        rng = null;

        System.Runtime.InteropServices.Marshal.ReleaseComObject(ws);
        ws = null;

        wb.Close(true, ImportPath, null);
        System.Runtime.InteropServices.Marshal.ReleaseComObject(wb);
        wb = null;

        GC.Collect();

        app.Quit();
        System.Runtime.InteropServices.Marshal.ReleaseComObject(app);
        app = null;
    }

Answer 1

You need to call GC.Collect / GC.WaitForPendingFinalizers and Marshall.FinalReleaseComObject.

See my answer for more details:

How to clean Excel interaction objects correctly?

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