NullReferenceException error in VB Application?

Question

I'm building a voting system for calls, and have tried to build it in VB. So far this is what I have:

    Dim con As New OleDb.OleDbConnection
    Dim dbProvider As String
    Dim dbSource As String

    dbProvider = "PROVIDER=Microsoft.Jet.OLEDB.4.0;"
    dbSource = "Data Source = C:\PhonePoll.mdb"

    con.ConnectionString = dbProvider & dbSource

    con.ConnectionString = "PROVIDER=Microsoft.Jet.OLEDB.4.0;Data Source = C:\PhonePoll.mdb"

    con.Open()

    'sql = "SELECT * FROM voting"
    'da = New OleDb.OleDbDataAdapter(sql, con)
    'da.Fill(ds, "voting")

    If inc <> -1 Then

        Dim cb As New OleDb.OleDbCommandBuilder(da)
        Dim dsNewRow As DataRow

        dsNewRow = ds.Tables("voting").NewRow()
        dsNewRow.Item("voted") = RadioButton1.Checked.ToString
        dsNewRow.Item("voted") = RadioButton2.Checked.ToString
        dsNewRow.Item("voted") = RadioButton3.Checked.ToString
        dsNewRow.Item("voted") = RadioButton4.Checked.ToString

        ds.Tables("voting").Rows.Add(dsNewRow)

        da.Update(ds, "voting")

        MsgBox("New Record added to the Database")

    End If

    MsgBox("Phone call has been logged")

    con.Close()

This code is contained within a "Record Call" button. On the form, there are four radio buttons, all with different text values which should be entered in to the "voting" table.

My problem is that when I select a radio button and click on "Record Button" it then displays this error:

NullReferenceException: Object reference not set to an instance of an object.

This error is displayed on the line

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

I'm not sure what I've done wrong.

Cheers for the help!

IniTech · Accepted Answer · 2011-04-11T21:48:27.047

2

I am assuming in the real code you don't have the SQL and Fill() method for the dataset commented out and that is just a typo in the code above - right? If I am wrong and that block of code is commented out, then your dataset is null and that's the issue...

edited Apr 11 '11 at 21:48

answered Apr 11 '11 at 21:37

IniTech

781
7
20

I can't understand it, I commented them out because it wasn't working in the first place. I've uncommented them now and it works? Thanks for the help! – mickburkejnr Apr 11 '11 at 22:30

score 0 · Answer 2 · answered Apr 11 '11 at 21:38

Don't put all that code on one line - Split it up. Either ds is null, or ds.Tables("voting") returns something null, but you will never know because it's transitory. And you can't check it, because you didn't store it in a variable

That's why I try to never calls too long:

A b = me.foo.bar.baz.fuz.bom() <- Just asking for trouble!

score 0 · Answer 3 · answered Apr 11 '11 at 21:41

0

ds is null, its not initialized

maybe if you unquote:

'sql = "SELECT * FROM voting"
'da = New OleDb.OleDbDataAdapter(sql, con)
'da.Fill(ds, "voting")

answered Apr 11 '11 at 21:41

Mark Mooibroek

7,636
3
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NullReferenceException error in VB Application?

3 Answers3