NullReferenceException fix?

Question

Im new with vb.net and I know i still got a lot to learn. Research and lots of sample codes help me improve my programming skill but then theres still alot of things to be confused about.

Here's an error I just encountered.

Dim drv As DataRowView
    If e.RowIndex >= 0 Then
        If e.RowIndex <= ds.Tables("entrancequestion").Rows.Count - 1 ***Then***
                                                                          'Object reference not set to an instance of an object.
            drv = ds.Tables("entrancequestion").DefaultView.Item(e.RowIndex)
            Dim c As Color
            If drv.Item("TimesAnswered").Value <= (Convert.ToDouble(lblappcount.Text) * 0.2) Then

                c = Color.Yellow
            ElseIf drv.Item("TimesAnswered").Value >= (Convert.ToDouble(lblappcount.Text) * 0.8) Then
                c = Color.Red
            Else
                c = Color.Black
            End If
            e.CellStyle.ForeColor = c
        End If
    End If

this was written under the DataGridView.Cellformatting event. basicly i just wanted to changethe rows text color on the datagridview along those conditions.

row forecolor changes to yellow if "TimesAnswered" is less than or equal to 20% of the value on lblappcount.text.
row forecolor changes to redif "TimesAnswered" is less than or equal to 80% value on lblappcount.text.
and row for color if conditions above was not satisfied.

any suggestions is greatly appreciated.

Use the debugger to figure out what is null.. Also, learn about the And operator. — SLaks
– SLaks, Commented Mar 14, 2014 at 18:52
possible duplicate of What is a NullReferenceException and how do I fix it? — Ňɏssa Pøngjǣrdenlarp
– Ňɏssa Pøngjǣrdenlarp, Commented Mar 14, 2014 at 20:31

Crono · Accepted Answer · 2014-03-14 19:35:58Z

2

Either ds is null or it does not contains a table named entrancequestion.

Use a little Assert magic here:

Debug.Assert(ds IsNot Nothing)

Dim tblEntranceQuestion As DataTable = ds.Tables("entrancequestion")

Debug.Assert(tblEntranceQuestion IsNot Nothing)

If e.RowIndex <= tblEntranceQuestion.Rows.Count - 1
    (...)

edited Mar 14, 2014 at 19:35

answered Mar 14, 2014 at 19:20

Crono

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Comments

earl chester siaotong · Accepted Answer · 2014-03-15 11:00:23Z

0

Got it. Here's what I did. under the Cell formatting event I wrote this one.

  For i As Integer = 0 To EntranceQuestionDataGridView.Rows.Count - 1
        If EntranceQuestionDataGridView.Rows(i).Cells(10).Value <= (Convert.ToDouble(lblappcount.Text) * 0.2) And EntranceQuestionDataGridView.Rows(i).Cells(10).Value > 0 Then
            EntranceQuestionDataGridView.Rows(i).DefaultCellStyle.BackColor = Color.Red
        ElseIf EntranceQuestionDataGridView.Rows(i).Cells(10).Value >= (Convert.ToDouble(lblappcount.Text) * 0.8) Then
            EntranceQuestionDataGridView.Rows(i).DefaultCellStyle.BackColor = Color.Yellow
        Else
            EntranceQuestionDataGridView.Rows(i).DefaultCellStyle.BackColor = Color.White
        End If
    Next

Thanks anyways guys. I learned lots of stuff :)

answered Mar 15, 2014 at 11:00

earl chester siaotong

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1 Comment

earl chester siaotong Over a year ago

Ooops. what I meant was I was able to get the desired output that I wanted. NOT that I was able to solve the NullReferenceException thingy

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