"Object reference not set to an instance of an object" while trying to create a Excel file using Interop

Question

I found this code on Internet to create a Excel file using Interop library:

object misValue = System.Reflection.Missing.Value;
xlWorkBook = xlApp.Workbooks.Add(misValue);
xlWorkSheet = (Excel.Worksheet)xlWorkBook.Worksheets.get_Item(1);
xlWorkSheet.Cells[1, 1] = "http://csharp.net-informations.com";
xlWorkBook.SaveAs("csharp-Excel.xls", Excel.XlFileFormat.xlWorkbookNormal, misValue, misValue, misValue, misValue, Excel.XlSaveAsAccessMode.xlExclusive, misValue, misValue, misValue, misValue, misValue);
xlWorkBook.Close(true, misValue, misValue);
xlApp.Quit();
releaseObject(xlWorkSheet);
releaseObject(xlWorkBook);
releaseObject(xlApp);
MessageBox.Show("Excel file created , you can find the file c:\\csharp-Excel.xls");

But I'm getting this error when I execute the code:

Object reference not set to an instance of an object

on this line:

xlWorkBook = xlApp.Workbooks.Add(misValue);

EDIT this is the stack trace:

System.NullReferenceException was unhandled
 HResult=-2147467261
 Message=Object reference not set to an instance of an object.
 Source=CMApp
 StackTrace:
 at WindowsFormsApplication1.ExcelDBUserControl.button3_Click(Object sender, EventArgs e) in d:\Private\Dropbox\Work\ClanMovil21Comunicaciones\Apps\WindowsFormsApplication1\WindowsFormsApplication1\ExcelDBUserControl.cs:line 332
 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 WindowsFormsApplication1.Program.Main() in d:\Private\Dropbox\Work\ClanMovil21Comunicaciones\Apps\WindowsFormsApplication1\WindowsFormsApplication1\Program.cs:line 20
 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.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
 at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
 at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
 at System.Threading.ThreadHelper.ThreadStart()
 InnerException: 

What's wrong?

• SLaks: Where do you get the error? What's the stack trace?
• Reynier: @SLaks sorry I edited the code and add the line where code break
• Reynier: @SLaks Excel.Application xlApp; I defined xlApp var already
• mikey: I would like to discourage you from creating Excel files using Interop -- it is almost always a bad idea. How about creating an excel file using one of the Excel XML formats? e.g. en.wikipedia.org/wiki/…
• Sten Petrov: @Reynier if you just defined the xlApp like you say you do then it obviously will be null and cause the exception. You need to put something in that variable, such as Steve's answer below

Answer 1

Probably missing in copy/paste?

Microsoft.Office.Interop.Excel.Application xlApp = new Microsoft.Office.Interop.Excel.Application();

• Reynier: you're right that was the problem also I'm newbie with C# but I'll take a look to mikey suggestion, I notice that Interop is to slow and I'll create a huge Excel files
• Steve: It is not only slow, but has a serious drawback. It requires Office installed on the customer PC and sometimes this is not available.