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BOOK: Professional Visual Basic 2008 ISBN: 978-0-470-19136-1
This is the forum to discuss the Wrox book Professional Visual Basic 2008 by Bill Evjen, Billy Hollis, Bill Sheldon, Kent Sharkey; ISBN: 9780470191361
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Old August 21st, 2008, 01:25 PM
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Default The DBNull Class and IsDBNull Function

Pages 25,26
The code does not do what the text indicates that it does.
"The first conditional is evaluated to True."
--- The first conditional is NOT evaluated to TRUE


        Dim sysNull As System.DBNull = System.DBNull.Value
        Dim strMyString As String = Nothing

        If strMyString Is sysNull Then
            Console.WriteLine("1st condition is true") 'line_added
            strMyString = "Initialize my String"
        End If
        If Not IsDBNull(strMyString) Then
            Console.WriteLine("2nd condition is true") 'line_added
            Console.WriteLine(strMyString)
        End If
        Console.WriteLine("Done with dbNull test ") 'line_added


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Old September 27th, 2008, 09:13 AM
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Default

You are correct. But this might have worked in a previous version of VB.NET, and the author of that code likely assumed it would still work. Either that, or the author THOUGHT that the code was correct but didn't bother to test it. That's about all I can think of right now.


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