[RESOLVED] System.Null ReferenceException : Object reference not set to an instance of an object

[sauce1979]

Currently working on the status bar for application. I would like the status bar to display message errors if a user makes an invalid entry.
I have a module which contains the main procedure and procedures to change the text property of my status bar. A Call is made to the procedures from one of the forms that requires the user input. The application compliles but I get an unhandled exception of type 'System.Null ReferenceException' Object reference not set to an instance of an object.

I have relevant code is shown below:

Module MainMod
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    Public sErrorMessage As String
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    Private frmFinancialCalculations As frmFinancialCalculations
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    Public Sub Main()
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        Application.Run(frmFinancialCalculations)
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    End Sub
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    Public Sub DisplayErrorMessage()
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        frmFinancialCalculations.sbFinancialCalculations.Text = sErrorMessage 'This is where exception is happening
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        MessageBox.Show(sErrorMessage, "Financial Calculations")
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    End Sub
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    Public Sub ClearErrorMessage()
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        frmFinancialCalculations.sbFinancialCalculations.Text = ""
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    End Sub
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End Module
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===================================================================================
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Private Sub btnCalculate_Click(ByVal sender As System.Object, _
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        ByVal e As System.EventArgs) Handles btnCalculate.Click
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        If rdoFutureValue.Checked = True Then ' Determine which radio buton is called
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            If ValidEntry(txtMonthlyInvestment.Text, 100, 1000) Then
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                If ValidEntry(txtInterestRate.Text, 0, 24) Then
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                    If ValidEntry(txtYears.Text, 1, 65) Then
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                        Me.CalculateFutureValue()
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                        txtFutureValue.Focus()
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                    Else
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                        sErrorMessage = "Years must be  a number between 1 and 65."
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                        Call DisplayErrorMessage()
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                        'MessageBox.Show("Years must be  a number between 1 and 65.", _
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                        '"Entry error")
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                        txtYears.Focus()
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                    End If
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                Else
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                    sErrorMessage = "Interest rate must be a number between 0 and 24."
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                    Call DisplayErrorMessage()
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                    'MessageBox.Show("Interest rate must be a number between 0 and 24.", _
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                    ' "Entry error")
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                    txtInterestRate.Focus()
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                End If
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            Else
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                sErrorMessage = "Monthly investment must be a number between 100 and 1,000."
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                Call DisplayErrorMessage()
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                'MessageBox.Show("Monthly investment must be a number between 100 and 1,000.", _
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                '"Entry error")
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                txtMonthlyInvestment.Focus()
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            End If
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        ElseIf rdoMonthlyInvestment.Checked = True Then
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            If ValidEntry(txtInterestRate.Text, 0, 24) Then
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                If ValidEntry(txtYears.Text, 1, 65) Then
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                    If ValidEntry(txtFutureValue.Text, 1000, 100000) Then
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                        Me.CalculateMonthlyInvestment()
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                        txtMonthlyInvestment.Focus()
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                    Else
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                        sErrorMessage = "Future Value must be a number between 1,000 and 1,000,00."
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                        Call DisplayErrorMessage()
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                        'MessageBox.Show("Future Value must be a number between 1,000 and 1,000,00.", _
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                        '"Entry error")
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                        txtFutureValue.Focus()
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                    End If
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                Else
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                    sErrorMessage = "Interest rate must be a number between 0 and 24."
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                    Call DisplayErrorMessage()
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                    'MessageBox.Show("Interest rate must be a number between 0 and 24.", _
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                    '"Entry error")
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                    txtInterestRate.Focus()
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                End If
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            Else
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                sErrorMessage = "Years must be  a number between 1 and 65."
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                Call DisplayErrorMessage()
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                'MessageBox.Show("Years must be  a number between 1 and 65.", _
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                '"Entry error")
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                txtYears.Focus()
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            End If
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        Else
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            sErrorMessage = "Years must be  a number between 1 and 65."
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            Call DisplayErrorMessage()
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            'MessageBox.Show("Please specify the calculation as Future Value or Monthly investment", _
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            '"Entry error")
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            GroupBox1.Focus() ' If no radio buttons are selected
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        End If
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    End Sub

Line 15 above is where the exception is occuring but I am not sure why. Any ideas?

[Shaggy Hiker]

The error is on line 5:

Private frmFinancialCalculations As frmFinancialCalculations

Needs to be:

Private frmFinancialCalculations As New frmFinancialCalculations

Otherwise you are just creating the space that will hold the form without actually creating the form to put into that space.

[sauce1979]

Thanks for that. I have spent the best part of 4 hours staring at the code trying to sort this out lol

cheers

[Shaggy Hiker]

When you get that particular error message, highlight each object or method that returns an object, in the line that throws the exception. One of them will be Nothing, and that is where your problem is. The line you said was throwing the exception was this one:

frmFinancialCalculations.sbFinancialCalculations.Text = sErrorMessage

The problem can't be in sErrorMessage, because it wouldn't make any difference if that was Nothing, since you aren't accessing any members of it. Therefore, what remains are these two:

frmFinancialCalculations and frmFinancialCalculations.sbFinancialCalculations

(the .Text is just a property of sbFinancialCalculations, and can be ignored because you are not accessing any members of it)

The first of those is obviously a form, while the second appears to be a member of the form. If either one was Nothing, then you would get that exception as you are accessing members of an object that doesn't exist. I first looked at your code to see how the form was declared, and saw right away that there was no New. That wasn't conclusive, as you could have been creating the instance elsewhere. However, the only safe place to be creating the instance was in Sub Main, and you weren't creating it there. Since no other place was suitable, it was clear that if that was not the problem in this specific case, it was still a problem overall.

[sauce1979]

Many thanks for that explanation. I have been going through Murachs beginning .net for 2 weeks. Thus I am just a beginner. Whilst I find the book quite informative, it doesn't give much help if any exceptions are thrown with the sample applications. What you have said makes perfect sense based on the knowledge I have gained so far. Many thanks for your help.