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Mark01Flag for United States of America

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VB.Net FileName is Used Before Warning

I am trying to work with two radio buttons in a simple VB.net app that allows a user to select and open a PDF using the Process object. One PDF will be assigned to each radio button. The code is shown below. I get the following warning: "Variable ‘fileName’ is used before it has been assigned a value. A null reference exception could result at runtime."

Please help resolve the error.

This is not homework for a class. It is self-study using books.

Code:
Public Class Form1

    Private Sub OpenFile(ByVal AFileName As String)
        Dim psi As New ProcessStartInfo()

        psi.UseShellExecute = True
        psi.FileName = AFileName
        Process.Start(psi)
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim fileName As String
        If RadioButton1.Checked = True Then
            fileName = "c:\test_3\johnson.pdf"
        End If
        If RadioButton2.Checked = True Then
            fileName = "c:\test_3\ross.pdf"
        End If
        MessageBox.Show("File name is: " + fileName)
        OpenFile(fileName)
    End Sub
End Class

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The warning occurs on the following line:
MessageBox.Show("File name is: " + fileName)

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SOLUTION
Avatar of Ryan Chong
Ryan Chong
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ASKER

@Eric: I get the following error with your code: 'IsNullOrWhiteSpace' is not a member of 'String'.

Code:
 Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim fileName As String

        If String.IsNullOrWhiteSpace(fileName) Then
            MessageBox.Show("file name is not set!!!")
        Else
            MessageBox.Show("File name is: " + fileName)
            OpenFile(fileName)
        End If

        If RadioButton1.Checked = True Then
            fileName = "c:\test_3\johnson.pdf"
        End If
        If RadioButton2.Checked = True Then
            fileName = "c:\test_3\ross.pdf"
        End If

        MessageBox.Show("File name is: " + fileName)
        OpenFile(fileName)

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The error is caused by:
        If String.IsNullOrWhiteSpace(fileName) Then

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@Ryan: Your code does not resolve the warning.
@mybosssucks: Your code worked!
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ASKER

Thank you Eric, myboss and Ryan.