Excel Background Process Not Closing

Question

An Excel background process remains open after each time I open and read a file with Iterop. After running the below method a few times I end up with a lot of Excel background processes. I realise this has been asked before various times but I have tried all the suggestions (and implemented them in the code below) and nothing worked. Could someone please help.

    public List<double> ReadExcelFile()
    {
        Application excelApp = null;
        Workbooks workbooks = null;
        Workbook workBook = null;
        Worksheet worksheet = null;
        Range excelRange = null;
        List<double> sheetValues = new List<double>();

        try
        {
            excelApp = new Application();
            workbooks = excelApp.Workbooks;
            workBook = workbooks.Open(f_inputFilePath,
               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, Type.Missing);
            worksheet = workBook.Sheets["Sheet1"];
            excelRange = worksheet.UsedRange;
            object[,] sheetValuesRaw = (object[,])excelRange.get_Value(XlRangeValueDataType.xlRangeValueDefault);

            for (int i = f_firstNumericValueIndex; i <= sheetValuesRaw.GetLength(0); i++)
                sheetValues.Add((double)sheetValuesRaw[i, 1]);
        }
        finally
        {
            workBook.Close(false, Type.Missing, Type.Missing);
            workbooks.Close();

            releaseObject(excelRange);
            releaseObject(worksheet);
            releaseObject(workbooks);
            releaseObject(workBook);

            excelApp.Quit();
            releaseObject(excelApp);
        }
        return sheetValues;
    }

    private void releaseObject(object obj)
    {
        try
        {
            Marshal.ReleaseComObject(obj);
            obj = null;
        }
        catch (Exception ex)
        {
            obj = null;
        }
        finally
        {
            GC.Collect();
            GC.WaitForPendingFinalizers();
        }
    }

Answer 1

I know this question is quite old, but I was running into this issue as well. The garbage collection did not work. I found another solution that seems to work. I added the following to my code and the background processes are removed.

try
        {
            SetExcelFiles(rdgsFilePath, unreadFilePath);
            if (rdgsFilePath != "") ProcessReadingsFile();
            if (unreadFilePath != "") ProcessUnreadFile();
        }
catch (Exception)
        {
            Data = new List<BadgeData>();
        }
finally
        {
            GC.Collect();
            GC.WaitForPendingFinalizers();
        }

        xlApp.Quit();

        System.Diagnostics.Process[] PROC = System.Diagnostics.Process.GetProcessesByName("EXCEL");
        foreach (System.Diagnostics.Process PK in PROC)
        {
            if (PK.MainWindowTitle.Length == 0)
            {
                PK.Kill();
            }
        }

Answer 2

I had a few problems with the Excel interop stuff myself a few weeks back. I managed to solve the process hang however by wrapping the method which uses the Excel functionality in a try-catch-finally statement.

So it would look something like this:

public List<double> MyResults() {
    try {
        return ReadExcelFile();
    }
    finally {
        GC.Collect();
        GC.WaitForPendingFinalizers();
    }
}

And you would call the 'MyResults' method in place of where ever you currently have 'ReadExcelFile' being called.

I found that by wrapping the Excel functionallity inside another try-catch-finally loop outside of the method using the Interop services, it allowed the Excel bits to go out of scope and allow the GC to collect them up.