Question

I’m trying to generate excel file using window form. I got error when trying to save the excel.

Method call from buttom

 ExportToExcel(dtResult, "C:\\Excel/test.xls");

Code for generate Excel

public void ExportToExcel( DataTable Tbl, string ExcelFilePath = null)
        {
            try
            {
                if (Tbl == null || Tbl.Columns.Count == 0)
                    throw new Exception("ExportToExcel: Null or empty input table!\n");

                // load excel, and create a new workbook
                Excel.Application excelApp = new Excel.Application();
                excelApp.Workbooks.Add();

                // single worksheet
                Excel._Worksheet workSheet = excelApp.ActiveSheet;

                // column headings
                for (int i = 0; i < Tbl.Columns.Count; i++)
                {
                    workSheet.Cells[1, (i + 1)] = Tbl.Columns[i].ColumnName;
                }

                // rows
                for (int i = 0; i < Tbl.Rows.Count; i++)
                {
                    // to do: format datetime values before printing
                    for (int j = 0; j < Tbl.Columns.Count; j++)
                    {
                        workSheet.Cells[(i + 2), (j + 1)] = Tbl.Rows[i][j];
                    }
                }

                // check fielpath
                if (ExcelFilePath != null && ExcelFilePath != "")
                {
                    try
                    {
                        workSheet.SaveAs(ExcelFilePath); //throws error here
                        excelApp.Quit();
                        MessageBox.Show("Excel file saved!");
                    }
                    catch (Exception ex)
                    {
                        throw new Exception("ExportToExcel: Excel file could not be saved! Check filepath.\n"
                            + ex.Message);
                    }
                }
                else    // no filepath is given
                {
                    excelApp.Visible = true;
                }
            }
            catch (Exception ex)
            {
                throw new Exception("ExportToExcel: \n" + ex.Message);
            }
        }

Error

System.Exception was unhandled
  Message=ExportToExcel: 
ExportToExcel: Excel file could not be saved! Check filepath.
Microsoft Excel cannot access the file 'C:\//5D95C000'. There are several possible reasons:

• The file name or path does not exist.
• The file is being used by another program.
• The workbook you are trying to save has the same name as a currently open workbook.
  Source=Report
  StackTrace:
       at Report.Form1.ExportToExcel(DataTable Tbl, String ExcelFilePath) in C:\SMARTAG_PROJECT\SUREREACH\EXCEL\Report\Report\Form1.cs:line 84
       at Report.Form1.button1_Click(Object sender, EventArgs e) in C:\SMARTAG_PROJECT\SUREREACH\EXCEL\Report\Report\Form1.cs:line 29
       at System.Windows.Forms.Control.OnClick(EventArgs e)
       at System.Windows.Forms.Button.OnClick(EventArgs e)
       at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
       at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
       at System.Windows.Forms.Control.WndProc(Message& m)
       at System.Windows.Forms.ButtonBase.WndProc(Message& m)
       at System.Windows.Forms.Button.WndProc(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
       at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
       at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
       at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.Run(Form mainForm)
       at Report.Program.Main() in C:\SMARTAG_PROJECT\SUREREACH\EXCEL\Report\Report\Program.cs:line 18
       at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
       at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
  InnerException: 

Answer 1

In order to get your file to save you need to make sure that you have a file extension at the end of the file path.

the filepath in your method here ExportToExcel(dtResult, "C:\\Excel/test.xls"); is incorrect
also make sure that you release the excelApp object correctly

instead of excelApp.Quit(); replace it with something like this

 System.Runtime.InteropServices.Marshal.ReleaseComObject( excelApp );