Cannot save Excel file after updating it in c# console app

Question

Information:

MS Excel Version Installed: Excel 2013 (Can try to change if required)

Reference Library Used: Microsoft Excel 15.0 Object Library (version 1.8)

.Net Framework: 4.7.2 (Cannot change)

Application Type: Console Application (Cannot change)

What I need:

So I have an excel workbook, which already has about 8000 rows each in first 2 sheets and some graphs in 4 other sheets. I need to add this data to the bottom of the existing data in one of the first 2 sheets, do a refresh, save it and close it.

This is what im doing:

    using MSExcel = Microsoft.Office.Interop.Excel;

In the class constructor--

    public UsageReportFileManager(string reportFolderPath)
    {
        excel = new MSExcel.Application();

        if (excel == null)
        {
            log.Error("-E-Unable to create report!!");
            throw new Exception("Microsoft excel is not installed on the client machine");
        }
        InitializeWorkbook();
    }

the Initialize Workbook function---

    private void InitializeWorkbook()
    {
        if (excel != null)
        {
            var filePath = GetResultPath(); //This returns a path which ends with .xlsx and it is a path to the existing file.

            if (!File.Exists(filePath)) //This is just handling a situation in case the actual file is missing.
            {
                //Create copy from template
                var templatePath = GetTemplateFilePath(); // this is not a excel template btw, its a empty workbook with formulas.
                File.Copy(templatePath, filePath);
                // Till here its working and new file is created if original file is missing
            }

            var missing = Missing.Value;
            _workbook = excel.Workbooks.Open(Filename: filePath, 
                UpdateLinks: missing, 
                ReadOnly: false, 
                Format: missing, 
                Password: missing, 
                WriteResPassword: missing, 
                IgnoreReadOnlyRecommended: true, 
                Origin: missing, 
                Delimiter: missing, 
                Editable: true, 
                Notify: missing, 
                Converter: missing, 
                AddToMru: true,
                Local: true
                );
        }
    }

In a separate function in this class which is called from Program.cs after this class is Initialized --

    public void UpdateLoginRawDataToWorkbook(List<HubAuditEvent> lstLoginData)
    {
            var dtLoginData = ConvertDataListToDatatable(lstLoginData); -- I will be getting more than 1500 rows here.

            if (dtLoginData.Rows.Count > 0)
            {
                MSExcel.Worksheet sheet = _workbook.Sheets["SheetAlreadyHasData"] as MSExcel.Worksheet;

                MSExcel.Range lastCell = sheet.Cells.Find(
                    "*",
                    Missing.Value,
                    Missing.Value,
                    Missing.Value,
                    MSExcel.XlSearchOrder.xlByRows,
                    MSExcel.XlSearchDirection.xlPrevious,
                    false,
                    Missing.Value,
                    Missing.Value);

                int lastRow = lastCell.Row;

                for (int i = 0; i < dtLoginData.Rows.Count; i++)
                {
                    int row = lastRow + i + 1;
                    for (int j = 0; j < dtLoginData.Columns.Count; j++)
                    {
                        var col = j + 1;
                        sheet.Cells[row, col] = dtLoginData.Rows[i][j].ToString();
                    }
                }

                _workbook.RefreshAll();
                excel.Calculate();
                _workbook.Save(); <-- I get an exception here saying Cannot Save Read-Only file ..
                _workbook.Close(true);
                excel.Quit();
      }

I get an exception at the _workbook.Save(); line saying Cannot Save Read-Only file ..

Answer 1

Okay so I post this as an answer and not a comment, because I believe many of us might be doing this same thing without even realising it.

Special thanks to @PanagiotisKanavos and @MikeJ: You just saved my day. Your comments got me thinking that did I really open the file "AGAIN" ?

I say "again" because this is what had happened...

1. So I open the file, check if its read-only and run my console app. (See here I forget to close the workbook on my desktop app)

2. Then in the middle of the debugging I get the exception that its open, so I stop the debugging the moment I see the exception. (Here first thing, because I was just testing I forgot to put the excel.Quit() in the finally block-- which I realize now is very very very important. And even if I had it in my finally block, the second mistake I was doing is I was stopping the app the moment I got the exception).

3. And now I had several instances of open excel objects which were not closed, because by now I had debugged several times. And since then no matter where I put excel.Quit(), that instance was somehow open somewhere for some reason.

4. Then I checked your comments and tried opening manually again and got the same error message that its read-only. And it was all crystal clear then.

5. Now I created a public method inside this FileManager class called Close() which looks like:

    public void Close() { if(excel != null && _workbook != null) { _workbook.Close(true); excel.Quit(); } }

Now I called this Close() method from the finally block in my Program.cs class.

6. Then I had to literally restart my machine to release that lock :D.

And now its working fine. :)