Excel process remains open after interop; traditional method not working

Question

I'm running into an issue with some code I'm debugging. Excel interop is used to extract some values from a workbook; however, Excel remains open after the program has exited. I've tried the traditional solution, but it still keeps a reference to Excel open on all machines where the code is run

private void TestExcel()
    {
        Excel.Application excel = new Excel.Application();
        Excel.Workbooks books = excel.Workbooks;
        Excel.Workbook book = books.Open("C:\\test.xlsm");

        book.Close();
        books.Close();
        excel.Quit();

        Marshal.ReleaseComObject(book);
        Marshal.ReleaseComObject(books);
        Marshal.ReleaseComObject(excel);
    }

Even this simple piece of code keeps the process running with multiple files (xlsm, xlsx, xls). Right now we have a workaround in place to kill the Excel processes we've opened, but I'd much rather get this working for my own sanity.

I should add that I have it narrowed down to the Workbook variable. If I remove the call to books.Open() and all references to book then it closes successfully.

Answer 1

This code works for me.

//Declare separate object variables
Excel.Application xlApp = new Excel.Application();
Excel.Workbooks xlWorkbooks = xlApp.Workbooks;
Excel.Workbook xlWorkbook = xlWorkbooks.Add(Missing.Value);
Excel.Worksheet xlWorksheet = (Excel.Worksheet)xlWorkbook.Worksheets.get_Item(1);

//Create worksheet

xlWorkbook.Close(false, Missing.Value, Missing.Value);
xlWorkbooks.Close();
xlApp.Quit();

Marshal.FinalReleaseComObject(xlWorksheet);
Marshal.FinalReleaseComObject(xlWorkbook);
Marshal.FinalReleaseComObject(xlWorkbooks);
Marshal.FinalReleaseComObject(xlApp);

xlWorksheet = null;
xlWorkbook = null;
xlWorkbooks = null;
xlApp = null;

GC.Collect();

This article from Microsoft has some good information regarding this issue.

Answer 2

This has worked successfully for me:

        xlApp.Quit();

        //release all memory - stop EXCEL.exe from hanging around.
        if (xlWorkBook != null) { Marshal.ReleaseComObject(xlWorkBook); } //release each workbook like this
        if (xlWorkSheet != null) { Marshal.ReleaseComObject(xlWorkSheet); } //release each worksheet like this
        if (xlApp != null) { Marshal.ReleaseComObject(xlApp); } //release the Excel application
        xlWorkBook = null; //set each memory reference to null.
        xlWorkSheet = null;
        xlApp = null;
        GC.Collect();

Answer 3

I am a total COM amateur, used it for a minor thing in one project quite a long time ago, but here's a snippet I used there. I probably found it somewhere online, don't remember. In any case, I paste it its full glory ;)

public static class ComBlackBox
{
    public static void ReleaseObject(object obj)
    {
        try
        {
            System.Runtime.InteropServices.Marshal.ReleaseComObject(obj);
            obj = null;
        }
        catch (ArgumentException ex)
        {
            obj = null;
            MessageBox.Show("Unable to release the Object " + ex.Message);
        }
        finally
        {
            GC.Collect();
        }
    } 
}

I'm unable to try it out now, but it probably worked (I honestly don't remember any details). Maybe it will help you out. Feel free to point out any obvious problems with this code, I really am far from being COM-literate ;)

Answer 4

This is how I got around this problem:

// Store the Excel processes before opening.
Process[] processesBefore = Process.GetProcessesByName("excel");

// Open the file in Excel.
Application excelApplication = new Application();
Workbook excelWorkbook = excelApplication.Workbooks.Open(Filename);

// Get Excel processes after opening the file.
Process[] processesAfter = Process.GetProcessesByName("excel");

// Now find the process id that was created, and store it.
int processID = 0;
foreach (Process process in processesAfter)
{
    if (!processesBefore.Select(p => p.Id).Contains(process.Id))
    {
        processID = process.Id;
    }
}

// Do the Excel stuff

// Now close the file with the COM object.
excelWorkbook.Close();
excelApplication.Workbooks.Close();
excelApplication.Quit();

// And now kill the process.
if (processID != 0)
{
    Process process = Process.GetProcessById(processID);
    process.Kill();
}