Cannot close Excel.exe after Interop process

Question

I'm having an issue with Excel Interop.

The Excel.exe doesn't close even if when I realease instances.

Here is my code :

using xl = Microsoft.Office.Interop.Excel;


xl.Application excel = new xl.Application();
excel.Visible = true;
excel.ScreenUpdating = false;
if (wordFile.Contains(".csv") || wordFile.Contains(".xls"))
{
   //typeExcel become a string of the document name
   string typeExcel = wordFile.ToString();
   xl.Workbook workbook = excel.Workbooks.Open(typeExcel,
                                                oMissing,  oMissing,  oMissing,  oMissing,
                                                oMissing,  oMissing,  oMissing,  oMissing,
                                                oMissing,  oMissing,  oMissing,  oMissing,
                                                oMissing,  oMissing);
   object outputFileName = null;
   if (wordFile.Contains(".xls"))
   {
     outputFileName = wordFile.Replace(".xls", ".pdf");
   }
   else if (wordFile.Contains(".csv"))
   {
     outputFileName = wordFile.Replace(".csv", ".pdf");
   }

   workbook.ExportAsFixedFormat(XlFixedFormatType.xlTypePDF, outputFileName, 
                                 XlFixedFormatQuality.xlQualityStandard, oMissing,
                                 oMissing, oMissing, oMissing, oMissing, oMissing);

   object saveChanges = xl.XlSaveAction.xlDoNotSaveChanges;
   ((xl._Workbook)workbook).Close(saveChanges, oMissing, oMissing);

   Marshal.ReleaseComObject(workbook);
   workbook = null;
}

I saw that, with the Marshal.RealeaseComObject it should be work, but nothing. How can I fix this?

Thank you.

Answer 1

Rules - never use no more that one dot

-- one dot

var range = ((Range)xlWorksheet.Cells[rowIndex, setColumn]);
var hyperLinks = range.Hyperlinks;
hyperLinks.Add(range, data);

-- Two or more dots

 (Range)xlWorksheet.Cells[rowIndex, setColumn]).Hyperlinks.Add(range, data);

-- Example

 using Microsoft.Office.Interop.Excel;

 Application xls = null;
 Workbooks workBooks = null;
 Workbook workBook = null;
 Sheets sheets = null;
 Worksheet workSheet1 = null;
 Worksheet workSheet2 = null;

 workBooks = xls.Workbooks;
 workBook = workBooks.Open(workSpaceFile);
 sheets = workBook.Worksheets;
 workSheet1 = (Worksheet)sheets[1];


// removing from Memory
 if (xls != null)
 {    
   foreach (Microsoft.Office.Interop.Excel.Worksheet sheet in sheets)
   {
      ReleaseObject(sheet);
   }

   ReleaseObject(sheets);
   workBook.Close();
   ReleaseObject(workBook);
   ReleaseObject(workBooks);

   xls.Application.Quit(); // THIS IS WHAT IS CAUSES EXCEL TO CLOSE
   xls.Quit();
   ReleaseObject(xls);

   sheets = null;
   workBook = null;
   workBooks = null;
   xls = null;

   GC.Collect();
   GC.WaitForPendingFinalizers();
   GC.Collect();
   GC.WaitForPendingFinalizers();
}

Answer 2

In case you are desperate. Do not use this approach unless you understand what it does:

foreach (Process proc in System.Diagnostics.Process.GetProcessesByName("EXCEL"))
{
  proc.Kill();
}

Note: This kill every process named "EXCEL".

I had to do it becase even though I've closed every single COM object in my code I still had stubborn Excel.exe process just hanging there. This is by no means the best solution, of course.

Answer 3

Simple rule: avoid using double-dot-calling expressions, such as this:

var workbook = excel.Workbooks.Open(/*params*/)

...because in this way you create RCW objects not only for workbook, but for Workbooks, and you should release it too (which is not possible if a reference to the object is not maintained).

So, the right way will be:

var workbooks = excel.Workbooks;
var workbook = workbooks.Open(/*params*/)

//business logic here

Marshal.ReleaseComObject(workbook);
Marshal.ReleaseComObject(workbooks);
Marshal.ReleaseComObject(excel);

Answer 4

@Denis Molodtsov in an attempt to be helpful suggested killing all processes named 'EXCEL'. That seems to be asking for trouble. There are already many answers that describe ways to get the process to stop after the call to excel.quit() by playing nice with COM interop. This is best if you can make it work.

@Kevin Vuilleumier had a great suggestion to send WM_CLOSE to the Excel window. I plan to test this.

If for some reason you need to kill an Excel App Object's Excel process, you can target it specifically using something like this:

  using System.Diagnostics;
  using System.Runtime.InteropServices;

// . . .

    [DllImport("user32.dll", SetLastError=true)]
    public static extern uint GetWindowThreadProcessId(IntPtr hWnd, out uint processId);

// . . .

    uint excelAppPid;
    uint tid = GetWindowThreadProcessId(excel.Hwnd, out excelAppPid);

    if (tid)
    {
      Process excelAppProc = Process.GetProcessById($excelPid)
      if (excelAppProc)
      {
        excelAppProc.Kill()
      }
    }

I don't have time to fully test in C#, but I ran a quick test in Powershell where I'm having a problem with Excel not terminating and this approach works.

It's pretty straightforward. Excel App object's Hwnd property is the Excel process's hidden window handle. Pass excel.Hwnd to GetWindowThreadProcessId to get the process ID. Use that to open the process, finally invoke Kill().

At least we're sure we're killing the right process. Well, pretty sure. If the Excel process already terminated normally, it's process ID could be reused by a new process. To limit this possibility, it's important not to wait between calling excel.quit() and attempting to kill.

Answer 5

As stated in other answers, using two dots will create hidden references that cannot be closed by Marshal.FinalReleaseComObject. I just wanted to share my solution, which eliminates the need to remember Marshal.FinalReleaseComObject - it's really easy to miss, and a pain to locate the culprit.

I use a generic IDisposable wrapper class which can be used on any COM object. It works like a charm, and it keeps everything nice and clean. I can even reuse private fields (e.g. this.worksheet). It also auto-releases the object when something throws an error, due to the nature of IDisposable (the Dispose method runs as a finally).

using Microsoft.Office.Interop.Excel;

public class ExcelService
{
    private _Worksheet worksheet;

    private class ComObject<TType> : IDisposable
    {
        public TType Instance { get; set; }

        public ComObject(TType instance)
        {
            this.Instance = instance;
        }

        public void Dispose()
        {
            System.Runtime.InteropServices.Marshal.FinalReleaseComObject(this.Instance);
        }
    }

    public void CreateExcelFile(string fullFilePath)
    {
        using (var comApplication = new ComObject<Application>(new Application()))
        {
            var excelInstance = comApplication.Instance;
            excelInstance.Visible = false;
            excelInstance.DisplayAlerts = false;

            try
            {
                using (var workbooks = new ComObject<Workbooks>(excelInstance.Workbooks))
                using (var workbook = new ComObject<_Workbook>(workbooks.Instance.Add()))
                using (var comSheets = new ComObject<Sheets>(workbook.Instance.Sheets))
                {
                    using (var comSheet = new ComObject<_Worksheet>(comSheets.Instance["Sheet1"]))
                    {
                        this.worksheet = comSheet.Instance;
                        this.worksheet.Name = "Action";
                        this.worksheet.Visible = XlSheetVisibility.xlSheetHidden;
                    }

                    using (var comSheet = new ComObject<_Worksheet>(comSheets.Instance["Sheet2"]))
                    {
                        this.worksheet = comSheet.Instance;
                        this.worksheet.Name = "Status";
                        this.worksheet.Visible = XlSheetVisibility.xlSheetHidden;
                    }

                    using (var comSheet = new ComObject<_Worksheet>(comSheets.Instance["Sheet3"]))
                    {
                        this.worksheet = comSheet.Instance;
                        this.worksheet.Name = "ItemPrices";
                        this.worksheet.Activate();

                        using (var comRange = new ComObject<Range>(this.worksheet.Range["A4"]))
                        using (var comWindow = new ComObject<Window>(excelInstance.ActiveWindow))
                        {
                            comRange.Instance.Select();
                            comWindow.Instance.FreezePanes = true;
                        }
                    }

                    if (this.fullFilePath != null)
                    {
                        var currentWorkbook = (workbook.Instance as _Workbook);
                        currentWorkbook.SaveAs(this.fullFilePath, XlFileFormat.xlWorkbookNormal);
                        currentWorkbook.Close(false);
                    }
                }
            }
            catch (Exception ex)
            {
                System.Diagnostics.Trace.WriteLine(ex.Message);
                throw;
            }
            finally
            {
                // Close Excel instance
                excelInstance.Quit();
            }
        }
    }
}

Answer 6

Alternatively, you can kill the Excel process as explained here.

First, import SendMessage function:

[DllImport("user32.dll", CharSet = CharSet.Auto)]
private static extern IntPtr SendMessage(IntPtr hWnd, int msg, IntPtr wParam, IntPtr lParam);

Then, send the WM_CLOSE message to the main window:

SendMessage((IntPtr)excel.Hwnd, 0x10, IntPtr.Zero, IntPtr.Zero);