hi there, im a beginner really and have just tried to finish a new computer based booking system for my work, im using sql and a database to store the customers and then store bookings too, but im having problems with the customer form, when i run it it kind of works until i click commit changes, when it throws an error A first chance exception of type 'System.NullReferenceException' occurred in LM_NewWork.exe

can you guys look at the code, and give suggestions to how to fix it and all to get it running, thanks, tell me where i have gone wrong with suggestions. feel free to edit the code.

Imports System.Data

Public Class Customers

    Dim inc As Integer
    Dim MaxavaliableRows As Integer
    Dim con As New OleDb.OleDbConnection
    Dim ds As New DataSet
    Dim da As OleDb.OleDbDataAdapter
    Dim sql As String

    Private Sub Qoutes_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        con.ConnectionString = "PROVIDER=Microsoft.Jet.OLEDB.4.0;Data Source = c:\LM_NewWork\DA_File.mdb"
        con.Open()
        sql = "SELECT * FROM tblCustomers"
        da = New OleDb.OleDbDataAdapter(sql, con)
        da.Fill(ds, "tblCustomers")

        txtcustomerid.Text = ds.Tables("tblCustomers").Rows(0).Item(1)
        txtforename.Text = ds.Tables("tblCustomers").Rows(0).Item(2)
        txtsurname.Text = ds.Tables("tblCustomers").Rows(0).Item(3)
        txtgroupname.Text = ds.Tables("tblCustomers").Rows(0).Item(4)
        txtdob.Text = ds.Tables("tblCustomers").Rows(0).Item(5)
        txtaddress.Text = ds.Tables("tblCustomers").Rows(0).Item(6)
        txttown.Text = ds.Tables("tblCustomers").Rows(0).Item(7)
        txtcounty.Text = ds.Tables("tblCustomers").Rows(0).Item(8)
        txtpostcode.Text = ds.Tables("tblCustomers").Rows(0).Item(9)
        txttelephone.Text = ds.Tables("tblCustomers").Rows(0).Item(10)

        con.Close()

        MaxavaliableRows = ds.Tables("tblCustomers").Rows.Count
        inc = -1


    End Sub

    Private Sub NavigateRecords()

        txtcustomerid.Text = ds.Tables("tblCustomers").Rows(inc).Item(1)
        txtforename.Text = ds.Tables("tblCustomers").Rows(inc).Item(2)
        txtsurname.Text = ds.Tables("tblCustomers").Rows(inc).Item(3)
        txtgroupname.Text = ds.Tables("tblCustomers").Rows(inc).Item(4)
        txtdob.Text = ds.Tables("tblCustomers").Rows(inc).Item(5)
        txtaddress.Text = ds.Tables("tblCustomers").Rows(inc).Item(6)
        txttown.Text = ds.Tables("tblCustomers").Rows(inc).Item(7)
        txtcounty.Text = ds.Tables("tblCustomers").Rows(inc).Item(8)
        txtpostcode.Text = ds.Tables("tblCustomers").Rows(inc).Item(9)
        txttelephone.Text = ds.Tables("tblCustomers").Rows(inc).Item(10)


    End Sub



    Private Sub btnexitcustomer_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnexitcustomer.Click
        Me.Hide()
        Mainmenu.Show()

    End Sub

    Private Sub btnnext_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnnext.Click

        If inc <> MaxavaliableRows - 1 Then
            inc = inc + 1
            NavigateRecords()
        Else
            MsgBox("No More Rows")
        End If

    End Sub

    Private Sub btnprevious_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnprevious.Click

        If inc > 0 Then
            inc = inc - 1
            NavigateRecords()
        ElseIf inc = -1 Then
            MsgBox("No Records Yet")
        ElseIf inc = 0 Then
            MsgBox("First Record")
        End If

    End Sub

    Private Sub btnlast_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnlast.Click

        If inc <> MaxavaliableRows - 1 Then
            inc = MaxavaliableRows - 1
            NavigateRecords()
        End If


    End Sub

    Private Sub btnfirst_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnfirst.Click

        If inc <> 0 Then
            inc = 0
            NavigateRecords()
        End If


    End Sub

    Private Sub btneditcustomer_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btneditcustomer.Click

        Dim cb As New OleDb.OleDbCommandBuilder(da)

        ds.Tables("tblCustomers").Rows(inc).Item(1) = txtcustomerid.Text
        ds.Tables("tblCustomers").Rows(inc).Item(2) = txtforename.Text
        ds.Tables("tblCustomers").Rows(inc).Item(3) = txtsurname.Text
        ds.Tables("tblCustomers").Rows(inc).Item(4) = txtgroupname.Text
        ds.Tables("tblCustomers").Rows(inc).Item(5) = txtdob.Text
        ds.Tables("tblCustomers").Rows(inc).Item(6) = txtaddress.Text
        ds.Tables("tblCustomers").Rows(inc).Item(7) = txttown.Text
        ds.Tables("tblCustomers").Rows(inc).Item(8) = txtcounty.Text
        ds.Tables("tblCustomers").Rows(inc).Item(9) = txtpostcode.Text
        ds.Tables("tblCustomers").Rows(inc).Item(10) = txttelephone.Text

        da.Update(ds, "tblCustomers")
        MsgBox("Data updated")


    End Sub

    Private Sub btnsavecustomer_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnsavecustomer.Click

        btncommit.Enabled = True
        btnsavecustomer.Enabled = False
        btneditcustomer.Enabled = False
        btndeletecustomer.Enabled = False

        txtcustomerid.Clear()
        txtforename.Clear()
        txtsurname.Clear()
        txtgroupname.Clear()
        txtdob.Clear()
        txtaddress.Clear()
        txttown.Clear()
        txtcounty.Clear()
        txtpostcode.Clear()
        txttelephone.Clear()


    End Sub

    Private Sub btncommit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btncommit.Click
        Dim cb As New OleDb.OleDbCommandBuilder(da)
        Dim dsNewRow As DataRow

        If inc <> -1 Then

            dsNewRow = ds.Tables("tblCustomers").NewRow()

            dsNewRow.Item("Customer ID") = txtcustomerid.Text
            dsNewRow.Item("Forename") = txtforename.Text
            dsNewRow.Item("Surname") = txtsurname.Text
            dsNewRow.Item("Group Name") = txtgroupname.Text
            dsNewRow.Item("Date Of Birth") = txtdob.Text
            dsNewRow.Item("Address") = txtaddress.Text
            dsNewRow.Item("Town") = txttown.Text
            dsNewRow.Item("County") = txtcounty.Text
            dsNewRow.Item("Postcode") = txtpostcode.Text
            dsNewRow.Item("Telephone") = txttelephone.Text


            ds.Tables("tblCustomers").Rows.Add(dsNewRow)
            da.Update(ds, "tblCustomers")
            MsgBox("New Record added to the Database")

            btncommit.Enabled = False
            btnsavecustomer.Enabled = True
            btneditcustomer.Enabled = True
            btndeletecustomer.Enabled = True

        End If


    End Sub

    Private Sub btndeletecustomer_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btndeletecustomer.Click

        If MessageBox.Show("Do you really want to Delete this Record?", "Delete", MessageBoxButtons.YesNo,MessageBoxIcon.Warning) = DialogResult.No Then

            MsgBox("Operation Cancelled")
            Exit Sub
        End If


        Dim cb As New OleDb.OleDbCommandBuilder(da)
        ds.Tables("tblCustomers").Rows(inc).Delete()
        MaxavaliableRows = MaxavaliableRows - 1
        inc = 0
        NavigateRecords()
        da.Update(ds, "tblCustomers")


    End Sub
End Class

try fixin line 14 with a semicolon at the end like this.

con.ConnectionString = "PROVIDER=Microsoft.Jet.OLEDB.4.0;Data Source = c:\LM_NewWork\DA_File.mdb;"

hope it helps

try fixin line 14 with a semicolon at the end like this.

con.ConnectionString = "PROVIDER=Microsoft.Jet.OLEDB.4.0;Data Source = c:\LM_NewWork\DA_File.mdb;"

hope it helps

thsnks for that, ill try it when i get home from work and post back with info,
thanks again if it works anyway !
well actually, thanks if it doesn't too, for trying :P

id did not fix it, there is an error

System.NullReferenceException was unhandled
  Message=Object reference not set to an instance of an object.
  Source=LM_NewWork
  StackTrace:
       at LM_NewWork.Customers.btncommit_Click(Object sender, EventArgs e) in H:\Liam Marney\New Coursework\LM_NewWork\Customers.vb:line 155
       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 LM_NewCourseWork.My.MyApplication.Main(String[] Args) in 17d14f5c-a337-4978-8281-53493378c1071.vb:line 81
       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:

if that is any help , i cant see what is wrong, it should work but it doesnt

dsNewRow = ds.Tables("tblCustomers").NewRow()

this is the error line, it says null reference exception was unhandled

Edited 5 Years Ago by nomorelogic: n/a

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