Get Excel Active Worksheet with C#

Question

I am wondering why this code gets the open worksheet when I run it in debug, and catch an exception when I run it with no debug..

Excel.Application xlApp = null;
Excel.Workbook xlWBook = null;
Excel.Worksheet xlWSheet = null;
Excel.Range xlRange = null;
try {
    xlApp = (Excel.Application) Marshal.GetActiveObject("Excel.Application");
    xlApp.Visible = true;
    xlWBook = xlApp.ActiveWorkbook;
    xlWSheet = xlWBook.ActiveSheet;
    xlRange = xlWSheet.UsedRange;
    logResult = logResult + "Agganciato " + xlWBook.Name + " \r\n";
} catch {
    logResult = logResult + "Nessun file aperto rilevato. \r\n";
}

Any suggestion?

Answer 1

The following shows how one can use Excel Interop to either interact with an open Excel workbook or create a new workbook if one isn't open.

Try the following:

Add Reference (Option 1)

• Download / install NuGet package: Microsoft.Office.Interop.Excel

Add Reference (Option 2)

• In VS menu, click Project
• Select Add Reference...
• Click COM
• Check Microsoft Excel xx.x Object Library (ex: Microsoft Excel 16.0 Object Library)

Add the following using directives :

• using Excel = Microsoft.Office.Interop.Excel;
• using System.Runtime.InteropServices;
• using System.IO;
• using System.Diagnostics;

CreateExcelWorkbook

public void CreateExcelWorkbook(string filename)
{
    bool isExcelAlreadyRunning = false;
    string logResult = string.Empty;
    Excel.Application xlApp = null;
    Excel.Workbook xlWBook = null;
    Excel.Worksheet xlWSheet = null;
    Excel.Range xlRange = null;
    try
    {
        try
        {
            //if Excel isn't open, this will throw a COMException
            xlApp = (Excel.Application)Marshal.GetActiveObject("Excel.Application");

            //set value
            isExcelAlreadyRunning = true;
        }
        catch (System.Runtime.InteropServices.COMException ex)
        {
            //create new instance
            xlApp = new Excel.Application();
        }

        //whether or not to make Excel visible
        xlApp.Visible = true;

        //prevent prompting to overwrite existing file
        xlApp.DisplayAlerts = false;

        //disable user control while modifying the Excel Workbook
        //to prevent user interference
        //only necessary if Excel application Visibility property = true
        //need to re-enable before exitin this method
        //xlApp.UserControl = false;

        if (xlApp.Workbooks.Count > 0)
            xlWBook = xlApp.ActiveWorkbook;
        else
            xlWBook = xlApp.Workbooks.Add();

        if (xlWBook.Worksheets.Count > 0)
            xlWSheet = xlWBook.ActiveSheet;
        else
            xlWSheet = xlWBook.Sheets.Add();

        xlRange = xlWSheet.UsedRange;

        //set value
        xlWSheet.Cells[1, 1] = $"Test {DateTime.Now.ToString("HH:mm:ss.fff")}";

        //save Workbook - if file exists, overwrite it
        // xlWBook.SaveAs(filename, Excel.XlFileFormat.xlWorkbookDefault, System.Reflection.Missing.Value, System.Reflection.Missing.Value, true, false, Excel.XlSaveAsAccessMode.xlNoChange, Excel.XlSaveConflictResolution.xlLocalSessionChanges, System.Reflection.Missing.Value, System.Reflection.Missing.Value, System.Reflection.Missing.Value, System.Reflection.Missing.Value);
        xlWBook.SaveAs(filename, System.Reflection.Missing.Value, System.Reflection.Missing.Value, System.Reflection.Missing.Value, System.Reflection.Missing.Value, System.Reflection.Missing.Value, Excel.XlSaveAsAccessMode.xlNoChange, System.Reflection.Missing.Value, System.Reflection.Missing.Value, System.Reflection.Missing.Value, System.Reflection.Missing.Value, System.Reflection.Missing.Value);

        logResult = logResult + "Agganciato " + xlWBook.Name + " \r\n";
    }
    catch
    {
        logResult = logResult + "Nessun file aperto rilevato. \r\n";
    }
    finally
    {
        if (xlWBook != null)
        {
            System.Runtime.InteropServices.Marshal.ReleaseComObject(xlRange);
            System.Runtime.InteropServices.Marshal.ReleaseComObject(xlRange);
            System.Runtime.InteropServices.Marshal.ReleaseComObject(xlWSheet);

            xlWSheet = null;
            xlRange = null;

            if (!isExcelAlreadyRunning)
            {
                //close workbook
                xlWBook.Close(false);
            }

            //release all resources
            System.Runtime.InteropServices.Marshal.ReleaseComObject(xlWBook);

            xlWBook = null;
        }

        System.Threading.Thread.Sleep(150);

        if (xlApp != null)
        {
            if (!isExcelAlreadyRunning)
            {
                xlApp.Quit();
            }

            //release all resources
            System.Runtime.InteropServices.Marshal.ReleaseComObject(xlApp);
            System.Runtime.InteropServices.Marshal.FinalReleaseComObject(xlApp);

            xlApp = null;

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

            System.Threading.Thread.Sleep(175);
        }
    }
}

Usage :

CreateExcelWorkbook(filename);

//the following is necessary otherwise the Excel process seems to persist in Task Manager
GC.Collect();
GC.WaitForPendingFinalizers();
GC.Collect();
GC.WaitForPendingFinalizers();

Resources :

• Microsoft.Office.Interop.Excel Namespace
• Excel is still running though I quit and released the object
• Cannot close Excel.exe after Interop process