Try to open my Excel file using C# and get an error

Question

I try to read my Exel file from code and received System.InvalidCastException:

Additional information: Unable to cast COM object of type \'System.__Co

Answer 1

Seems like you are using

    Microsoft.Office.Tools.Excel.Worksheet 

instead of

    Microsoft.Office.Interop.Excel.Worksheet

which is why you are getting an invalid cast exception.

Answer 2

Try the below code and see if it works, if not let us know what problems you have:

using Excel = Microsoft.Office.Interop.Excel;

namespace Excel_Sample
{
    public partial class YourClass
    {
        Excel.Application appExcel;
        Excel.Workbook newWorkbook;
        Excel.Worksheet objsheet;
        string file = @"D:\file.xlsx";

        static void excel_init()
        {
            if (System.IO.File.Exists(file))
            {
                //Start Excel and get Application object.
                appExcel = new Excel.Application();
                //Get a workbook.;
                newWorkbook = (Excel.Workbook)(appExcel.Workbooks.Open(file));

                int count = newWorkbook.Worksheets.Count;
                if (count > 0)
                {
                    //Get Your Worksheet
                    objsheet = (Excel.Worksheet)newWorkbook.ActiveSheet;
                }
            }
            else
            {
                MessageBox.Show("Unable to open file!");
                System.Runtime.InteropServices.Marshal.ReleaseComObject(appExcel);
                appExcel = null;
                System.Windows.Forms.Application.Exit();
            }
        }
    }
}

Answer 3

Workbook.ActiveSheet Property might not be the best choice for programmatically opened Excel files as it can actually return a non-Worksheet object

You might want to consider checking sheets count and using indexes:

int count = newWorkbook.Worksheets.Count;
if (count > 0)
{
    objsheet = (Worksheet) newWorkbook.Worksheets[1];
}

And try not to break the 2-dot rule - you'll need to release all you COM's to properly close your app and Excel.

Edited:

You could be mixing Microsoft.Office.Interop.Excel with Microsoft.Office.Tools.Excel namespaces.

Try to declare and assign as follows:

private static Microsoft.Office.Interop.Excel.Worksheet objsheet = null;
...
objsheet = (Microsoft.Office.Interop.Excel.Worksheet) newWorkbook.Worksheets[1];