Upgrading VB6 to VB.NET

Introduction

I'm currently working for a company where I have to upgrade over 50 VB6 programs to VB.NET 2008. So far I'm about half way through, and I've learned quite a few tricks that drastically improve the performance of VB.NET apps.

Because there are a lot of programmers that are going to be making this move, I thought I would share this information. I'm certain it will be very valuable to those who are faced with this task.

One of the first things to think about is whether you want to upgrade your VB6 program to a VB.NET 2008 Windows Forms application or a VB.NET 2008 Windows Presentation Foundation (WPF) application. If you are upgrading to VB.NET 2005, then you don't have the WPF option, but if you are upgrading to VB.NET 2008, then you do, and you may choose to use it.

Why would you want to upgrade a VB6 Windows Forms application to WPF? Because that is the future of Windows programming. Windows Forms have been using the same technology for more than 15 years, and are now at the very beginning of their sunset. Windows Forms applications use User32 (User before 32-bit) and GDI/GDI+ for gui rendering, but WPF applications use DirectX for gui rendering, which is much more powerful. Additionally, WPF uses Extensible Application Markup Language (XAML) to define the layout of the interface, and instantiate .NET objects.

By far, the easiest choice is to upgrade a VB6 Windows Forms application to a VB.NET 2008 Windows Forms application. Since Windows Forms are going to be around for quite a while, we'll take a look at that.

Here are some steps and tips for upgrading a VB6 Windows Forms application to a VB.NET 2008 Windows Forms Application:

     1.  Use VS 2008's Upgrade Wizard
     2.  Change the Target Framework
     3.  Delete the Upgrade Report
     4.  Correct all errors
     5.  Update Code
     6.  Add API's to increase DoEvents performance.

Performing the upgrade

Instr(myString, "search for this string")     'Old way
myString.IndexOf("search for this string")    'New way

- Mid - Instead of using the Mid() method to get a portion of a string, use the SubString() method.

Mid(myString, 14)         'Old way
myString.SubString(13)    'New way

- Trim - Instead of using the Trim(), LTrim() and RTrim(), use .Trim(), .TrimStart(), .TrimEnd()

Trim(myString), LTrim(myString), RTrim(myString)             'Old way
myString.Trim(), myString.TrimStart(), mystring.TrimEnd()    'New way

- Len - Instead of using the Len() method, use .Length() to get the length of a string.

Len(myString)        'Old way
myString.Length()    'New way

- Replace the "And" operator with "AndAlso".  (Do this in any non-bitwise comparison).

If 1 = 1 And 2 = 2 And 3 = 3 Then            'And Old way
If 1 = 1 AndAlso 2 = 2 AndAlso 3 = 3 Then    'And New way

- Replace the "Or" operator with "OrElse".  (Do this in any non-bitwise comparison.)

If 1 = 1 Or 2 = 2 Or 3 = 3 Then            'Or old way
If 1 = 1 OrElse 2 = 2 OrElse 3 = 3 Then    'Or new way

- Replace ALL VB6 File I/O classes with the new .NET File I/O Classes. They are faster than VB6's so make sure you use them!

Dim myFile As String = "C:\Temp\myfile.txt"
Dim instring As String = String.Empty

'** VB6 File I/O:
FileOpen(1, myFile, OpenMode.Input)
Do Until EOF(1)
    instring = LineInput(1) 'Read 1 line from a file
Loop
FileClose(1)

'** VB.Net File I/O:
Dim reader As New System.IO.StreamReader(myFile)
Do Until reader.EndOfStream = True
    instring = reader.ReadLine()   'Read 1 line from a file
Loop
reader.Close()
reader.Dispose()

If you follow the steps and tips included in this article, then your upgrade should go pretty smoothly, and your application should perform quite a bit faster in VB.NET than it did in VB6.

Good luck!

VBRocks