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System.NullReferenceException
  HResult=0x80004003
  Message=Object reference not set to an instance of an object.
  Source=VBExportDataTableToExcel
  StackTrace:
   at VBExportDataTableToExcel.Form1.Button1_Click(Object sender, EventArgs e) in C:\Users\ALDEN FABRO\Documents\Visual\VBExportDataTableToExcel\VBExportDataTableToExcel\Form1.vb:line 111
   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 Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.OnRun()
   at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.DoApplicationModel()
   at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.Run(String[] commandLine)
   at VBExportDataTableToExcel.My.MyApplication.Main(String[] Args) in :line 83


What I have tried:

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
       Dim xlapp As Excel.Application
       Dim xlWorkBook As Excel._Workbook
       Dim xlWorkSheet As Excel.Worksheet
       Dim misValue As Object = System.Reflection.Missing.Value
       Dim i As Integer
       Dim j As Integer

       xlapp = New Excel.Application()
           xlWorkBook = xlapp.Workbooks.Add(misValue)
           xlWorkSheet = CType(xlWorkBook.Sheets("Sheet1"), Excel.Worksheet)

           For k = 0 To DataGridView1.ColumnCount - 1
               xlWorkSheet.Cells(1, k + 1).HorizontalAlignment = Microsoft.Office.Interop.Excel.XlHAlign.xlHAlignCenter
               xlWorkSheet.Cells(1, k + 1) = DataGridView1.Columns(k).Name
           Next
           For i = 0 To DataGridView1.RowCount - 1
               For j = 0 To DataGridView1.ColumnCount - 1
                   xlWorkSheet.Cells(i + 2, j + 1).HorizontalAlignment = Microsoft.Office.Interop.Excel.XlHAlign.xlHAlignCenter
                   xlWorkSheet.Cells(i + 2, j + 1) = DataGridView1(j, i).Value.ToString()
               Next
           Next

           Dim SaveFileDialog1 As New SaveFileDialog()
           SaveFileDialog1.Filter = "Excel files (*.xlsx)|*.xlsx"
           SaveFileDialog1.FilterIndex = 2
           SaveFileDialog1.RestoreDirectory = True
           If SaveFileDialog1.ShowDialog() = DialogResult.OK Then
               xlWorkSheet.SaveAs(SaveFileDialog1.FileName)
               MsgBox("Save file success")
           Else
               Return
           End If
           xlWorkBook.Close()
           xlapp.Quit()

   End Sub
Posted
Updated 22-Mar-22 20:58pm

1 solution

Read the error message:
System.NullReferenceException
  HResult=0x80004003
  Message=Object reference not set to an instance of an object.
  Source=VBExportDataTableToExcel

This is one of the most common problems we get asked, and it's also the one we are least equipped to answer, but you are most equipped to answer yourself.

Let me just explain what the error means: You have tried to use a variable, property, or a method return value but it contains null - which means that there is no instance of a class in the variable.
It's a bit like a pocket: you have a pocket in your shirt, which you use to hold a pen. If you reach into the pocket and find there isn't a pen there, you can't sign your name on a piece of paper - and you will get very funny looks if you try! The empty pocket is giving you a null value (no pen here!) so you can't do anything that you would normally do once you retrieved your pen. Why is it empty? That's the question - it may be that you forgot to pick up your pen when you left the house this morning, or possibly you left the pen in the pocket of yesterday's shirt when you took it off last night.

We can't tell, because we weren't there, and even more importantly, we can't even see your shirt, much less what is in the pocket!

Back to computers, and you have done the same thing, somehow - and we can't see your code, much less run it and find out what contains null when it shouldn't.
But you can - and Visual Studio will help you here. Run your program in the debugger and when it fails, it will show you the line it found the problem on. You can then start looking at the various parts of it to see what value is null and start looking back through your code to find out why. So put a breakpoint at the beginning of the method containing the error line, and run your program from the start again. This time, the debugger will stop before the error, and let you examine what is going on by stepping through the code looking at your values.

But we can't do that - we don't have your code, we don't know how to use it if we did have it, we don't have your data. So try it - and see how much information you can find out!
 
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