Excel process not terminating after use in C# console app

Question

I am creating spreadsheets in a C# console app using Excel. When I try to terminate the Excel process and get the window handle, I get an 'InvalidComObjectException' the second time through. The first Excel image in memory is deleted but thereafter Excel is not terminated. How can I fix this issue using .NET 4.8 and Windows 11?

Answer 1

Hi @Al Harlow , Welcome to Microsoft Q&A,

Maybe you want to see a use case of creating excel using c#:

using System;
using Excel = Microsoft.Office.Interop.Excel;

namespace ExcelCreationExample
{
     class Program
     {
         static void Main(string[] args)
         {
             //Create Excel application object
             Excel.Application excelApp = new Excel.Application();

             //Create a new workbook
             Excel.Workbook workbook = excelApp.Workbooks.Add();

             // Get the first worksheet
             Excel.Worksheet worksheet = workbook.Worksheets[1];

             //Write sample data in cell A1
             worksheet.Cells[1, 1] = "Hello";
             worksheet.Cells[1, 2] = "World";

             //Save workbook
             workbook.SaveAs("example.xlsx");

             // Close the workbook
             workbook.Close();

             // Close the Excel application
             excelApp.Quit();

             // Release the COM object
             ReleaseObject(worksheet);
             ReleaseObject(workbook);
             ReleaseObject(excelApp);
         }

         // Release the COM object
         static void ReleaseObject(object obj)
         {
             try
             {
                 System.Runtime.InteropServices.Marshal.ReleaseComObject(obj);
                 obj = null;
             }
             catch (Exception ex)
             {
                 obj = null;
                 Console.WriteLine("Exception Occured while releasing object " + ex.ToString());
             }
             finally
             {
                 GC.Collect();
             }
         }
     }
}

Best Regards,

Jiale

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Answer 2

You didn't post your code so I'm going to guess you are not properly cleaning up the references to the COM object. In addition to closing any Excel window you might have opened you also need to call Quit on the application. You need to ensure this happens even in the case of exceptions otherwise you'll leave processes hanging around.

Also note that even after you clean up a COM object the underlying COM runtime will potentially leave the process running for a while in case you try to start it again. It used to be 10 minutes IIRC but I don't know what the default is now. However if your app closes then it should close the other process as well provided you cleaned up all the resources properly.