System.NullReferenceException' occurred in WindowsApplication1.exe Additional information: Object reference not set to an instance of an object

Question

I am writing a very basic database input form for a sql database using vb.net

upon executing the code

dsnewrow = ds.Tables("Car Details").NewRow()

i am declaring dsnewrow just before this in the same sub here:

 Dim dsnewrow As DataRow

and ds is being declared here:

Dim ds As DataSet

in the public class of the form.

I understand that there is a problem with my ds variable, but I don't understand what it is,can anyone help?

full program:

Imports System.Data.SqlClient
Imports System.Windows.Forms

Public Class Form1
    Dim inc As Integer
    Dim ds As New DataSet
    Dim da As SqlDataAdapter
    Dim maxrows As Integer

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles btnDelete.Click
        Dim cb As SqlCommandBuilder = New SqlCommandBuilder(da)

        If MessageBox.Show("Are you sure that you want to delete this record?", _
                           "Delete", MessageBoxButtons.YesNo, _
                           MessageBoxIcon.Warning) = Windows.Forms.DialogResult.No Then
            MsgBox("Operation Cancelled")
        Else
            ds.Tables("Car Details").Rows(inc).Delete()
            maxrows = maxrows - 1
            inc = 0
            NavigateRecords()
            da.Update(ds, "authors2")
        End If

    End Sub

    Public Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Me.Car_DetailsTableAdapter.Fill(Me.CourseworkDataSet.Car_Details)
        Dim sqlstring As String
        Dim conn As SqlConnection
        Dim connstring As String


        connstring = "Data Source=(LocalDB)\v11.0;AttachDbFilename=C:\Users\Daniel\Documents\Coursework.mdf;Integrated Security=True;Connect Timeout=30"

        conn = New SqlConnection(connstring)
        conn.Open()
        MsgBox("successful")

        sqlstring = "SELECT * FROM Car Details"
        da = New SqlDataAdapter(sqlstring, conn)
        ds = New DataSet
        da.Fill(ds, "Car Details")

        conn.Close()
        conn = Nothing

        maxrows = ds.Tables("Car Details").Rows.Count
        inc = 0
        navigaterecords()
    End Sub

    Private Sub Car_DetailsBindingNavigatorSaveItem_Click(sender As Object, e As EventArgs) Handles Car_DetailsBindingNavigatorSaveItem.Click
        Me.Validate()
        Me.Car_DetailsBindingSource.EndEdit()
        Me.TableAdapterManager.UpdateAll(Me.CourseworkDataSet)

    End Sub

    Private Sub NavigateRecords()
        MakeTextBox.Text = ds.Tables("Car Details").Rows(inc).Item(0)
        ModelTextBox.Text = ds.Tables("Car Details").Rows(inc).Item(1)
        Engine_SizeTextBox.Text = ds.Tables("Car Details").Rows(inc).Item(2)
        ColourTextBox.Text = ds.Tables("Car Details").Rows(inc).Item(3)
        DoorsTextBox.Text = ds.Tables("Car Details").Rows(inc).Item(4)
        Buy_PriceTextBox.Text = ds.Tables("Car Details").Rows(inc).Item(5)
        Sell_PriceTextBox = ds.Tables("Car Details").Rows(inc).Item(6)

    End Sub

    Private Sub btnFwd_Click(sender As Object, e As EventArgs) Handles btnFwd.Click
        If inc <> maxrows - 1 Then
            inc = inc + 1
            NavigateRecords()
        Else
            MsgBox("No More Records")

        End If
    End Sub

    Private Sub btnBack_Click(sender As Object, e As EventArgs) Handles btnBack.Click
        If inc > 0 Then
            inc = inc - 1
            NavigateRecords()
        Else
            MsgBox("First Record")
        End If
    End Sub

    Private Sub btnFirst_Click(sender As Object, e As EventArgs) Handles btnFirst.Click
        If inc <> 0 Then
            inc = 0
            NavigateRecords()
        End If

    End Sub

    Private Sub btnLast_Click(sender As Object, e As EventArgs) Handles btnLast.Click
        If inc <> maxrows - 1 Then
            inc = maxrows - 1
            NavigateRecords()

        End If
    End Sub

    Private Sub btnUpdate_Click(sender As Object, e As EventArgs) Handles btnUpdate.Click
        Dim cb As SqlCommandBuilder = New SqlCommandBuilder(da)
        ds.Tables("Car Details").Rows(inc).Item(0) = MakeTextBox.Text
        ds.Tables("Car Details").Rows(inc).Item(1) = ModelTextBox.Text
        ds.Tables("Car Details").Rows(inc).Item(2) = Engine_SizeTextBox.Text
        ds.Tables("Car Details").Rows(inc).Item(3) = ColourTextBox.Text
        ds.Tables("Car Details").Rows(inc).Item(4) = DoorsTextBox.Text
        ds.Tables("Car Details").Rows(inc).Item(5) = Buy_PriceTextBox.Text
        ds.Tables("Car Details").Rows(inc).Item(6) = Sell_PriceTextBox.Text

    End Sub

    Private Sub btnAdd_Click(sender As Object, e As EventArgs) Handles btnAdd.Click
        btnUpdate.Enabled = False
        btnAdd.Enabled = False
        btnConfirm.Enabled = True
        btnDelete.Enabled = False

        ModelTextBox.Clear()
        MakeTextBox.Clear()
        Engine_SizeTextBox.Clear()
        ColourTextBox.Clear()
        DoorsTextBox.Clear()
        Buy_PriceTextBox.Clear()
        Sell_PriceTextBox.Clear()
    End Sub

    Private Sub btnConfirm_Click(sender As Object, e As EventArgs) Handles btnConfirm.Click
        If inc <> -1 Then
            Dim cb As SqlCommandBuilder = New SqlCommandBuilder(da)
            Dim dsnewrow As DataRow

            dsnewrow = ds.Tables("Car Details").NewRow()

            dsnewrow.Item("Make") = MakeTextBox.Text
            dsnewrow.Item("Model") = ModelTextBox.Text
            dsnewrow.Item("Engine Size") = Engine_SizeTextBox.Text
            dsnewrow.Item("Colour") = ColourTextBox.Text
            dsnewrow.Item("Doors") = DoorsTextBox.Text
            dsnewrow.Item("Buy Price") = Buy_PriceTextBox.Text
            dsnewrow.Item("Sell Price") = Sell_PriceTextBox.Text

            btnConfirm.Enabled = False
            btnAdd.Enabled = True
            btnUpdate.Enabled = True
            btnDelete.Enabled = True

        End If
    End Sub

    Private Sub btnCancel_Click(sender As Object, e As EventArgs) Handles btnCancel.Click
        btnUpdate.Enabled = True
        btnAdd.Enabled = True
        btnConfirm.Enabled = True
        btnDelete.Enabled = True
        inc = 0
        NavigateRecords()
    End Sub
    End Class

can you show more of your code please?

Malachi
– Malachi

2013-08-13 16:23:15 +00:00
Commented Aug 13, 2013 at 16:23 — Malachi
– Malachi, Commented Aug 13, 2013 at 16:23
Dim ds As new DataSet

bansi
– bansi

2013-08-13 16:24:04 +00:00
Commented Aug 13, 2013 at 16:24 — bansi
– bansi, Commented Aug 13, 2013 at 16:24
Can post the error message you get?

David Sdot
– David Sdot

2013-08-13 16:46:02 +00:00
Commented Aug 13, 2013 at 16:46 — David Sdot
– David Sdot, Commented Aug 13, 2013 at 16:46
the error is the title of the question

Daniel Barrow
– Daniel Barrow

2013-08-13 22:53:08 +00:00
Commented Aug 13, 2013 at 22:53 — Daniel Barrow
– Daniel Barrow, Commented Aug 13, 2013 at 22:53

bansi · Accepted Answer · 2013-08-13 16:27:00Z

2

You are only declaring the variable ds. You should create an instance, before you can use the methods.

Dim ds As DataSet

should be

Dim ds As New DataSet

or

Dim ds As DataSet
ds = New DataSet

answered Aug 13, 2013 at 16:27

bansi

57.3k6 gold badges44 silver badges52 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Steve · Accepted Answer · 2013-08-13 16:38:18Z

2

This line in Form_Load is wrong

sqlstring = "SELECT * FROM Car Details"

A table name when contains spaces should be enclosed in square brackets

sqlstring = "SELECT * FROM [Car Details]"

when you execute the query it doesn't work and your dataset is never initialized with new. Then when you try to use it you get the NULL Reference Exception. I suppose that you run this code on a 64bit system where the exceptions in a Form_Load event are ignored

edited Aug 13, 2013 at 16:38

answered Aug 13, 2013 at 16:31

Steve

217k22 gold badges242 silver badges296 bronze badges

5 Comments

Daniel Barrow Over a year ago

Correcting that still returns the same error, but thank you for picking up on that, clearly I need to read more around my lecture material!

Steve Over a year ago

It fails on the same line?

Daniel Barrow Over a year ago

yeah, exactly the same place

Steve Over a year ago

I suggest to put a breakpoint in that line and when hit, hover with your cursor on the variable ds to see if it is null, Check also if you have a table named Car Details in your dataset

Daniel Barrow Over a year ago

ds is [system.data.dataset]. I have a table calld Car Details in the Data Connections panel,and I have the table present in the data set.

Collectives™ on Stack Overflow

System.NullReferenceException' occurred in WindowsApplication1.exe Additional information: Object reference not set to an instance of an object

2 Answers 2

Comments

5 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

5 Comments

Your Answer

Sign up or log in

Post as a guest

Related