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Upgrading VB6 to VB.NET  (Performance Improvements)

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:

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

1. Using the Visual Studio 2008 Upgrade Wizard

     Open Visual Studio 2008
     From the File menu, select Open | Project/Solution

         -  Navigate to the VB6 project that you want to upgrade, and select it.
         -  The Upgrade Wizard will start automatically.
         -  Click "Next" through each window of the Wizard until the Wizard begins the conversion.
     ** Upgrade Errors:
     I have encountered some VB6 projects that did not complete the Upgrade Wizard, and would not
     upgrade. A couple of the errors I received were:  "Upgrade failed:  General error accessing file 'C'"
     and "Unable to read the project file..."  

     If you have a problem upgrading a VB6 application to VB.NET, then you have 3 options:

          1.  Install Visual Studio 2008 Service Pack 1 (SP1) and try it again.

          2.  Use the command-line version of the Wizard.  
               This is the same Upgrade engine that is used by the VS IDE Upgrade Wizard, but for some reason
               it worked every time a VB6 program crashed during upgrade.  Here's how:

                   -  Create a folder on the C:\ with a short name (like "Upgrade")
                   -  Copy and paste the VB6 Project files into this folder.
                   -  Open a Visual Studio Command Prompt
                       (Windows XP:  Start button > All Programs > Microsoft Visual Studio 2008 > 
                       Visual Studio Tools > Visual Studio 2008 Command Prompt)

                            -  Make sure you are in the VB directory (mine opened to VC)

                                     -  Type "cd..", press Enter to move up 1 directory.
                                     -  Type "cd VB", press Enter to change directory.

                            -  Go to the VBUpgrade directory

                                     -  Type "cd VBUpgrade", press Enter.

                            -  Run the command-line version of the Upgrade Wizard:

                                     -  Include "VBUpgrade.exe"
                                     -  Include the input project path <filename>
                                     -  Include the new folder the VB.NET project will be created in (Output directory)

                                     VBUpgrade.exe <filename> /Out <directory>

                                     VBUpgrade.exe "C:\Upgrade\Project1.vbp" /Out "C:\Upgrade\VB Upgrade"                                      

                                     -  Press the Enter key after you type the above, and the Upgrade should begin.
          3.  If the command-line version of the Upgrade Wizard does not work for you, try
               contacting John Hart at Microsoft (, he may be able to help.

2. Change the Target Framework

     By default the Target Framework will be set to ".Net Framework 2.0".  You can use this if you want to.
     I changed it to ".Net Framework 3.5".  If you desire to do so, here's how:
          -  Click on the Project Menu | Properties
          -  Click the Compile tab
          -  Click the "Advanced Compile Options..." button at the bottom of the tab page
          -  Change the "Target framework" to ".Net Framework 3.5"
          -  Click "OK", then "Yes"

3. Delete the Upgrade Report

     When you perform an Upgrade using the Upgrade Wizard, an Upgrade Report is automatically generated.
     If you would like to look at the report, then Open the Solution Explorer in Visual Studio (View menu |
     Solution Explorer), and double-click "_UpgradeReport.htm".  I personally haven't used the report, so I
     delete it (right-click, Delete in Solution Explorer).

          - If you decide to delete the report, you'll also need to open Windows Explorer and navigate to your
            project folder, then delete the "_UpgradeReport_Files" folder.

            Example:  delete "C:\Upgrade\VB Upgrade\_UpgradeReport_Fil es"

4. Error Correction

     Once you upgrade your VB6 Windows Forms application to .NET, you will have lots of errors!  To see a
     list of errors, open the "Error List" (View menu | Error List).

     To actually go to an error, double-click an error from the Error List.  Visual Studio will automatically take
     you to the line of code where the error occurs.  

     Above the line of code where the error occurs, you will notice an "Upgrade Warning".  This warning
     describes the error, and provides a fairly helpful link that can help you get more information about the
     error, plus steps you can take to fix the error.  To use the link, hold down the control button and left-
     click it with your mouse.

          For example, if you had a CommonDialog control on your VB6 form, then you will receive an error
          informing you that the CommonDialog was not upgraded.  The helpful link will provide links to new
          controls that replace the CommonDialog, such as "OpenFileDialog", "SaveFileDialog", etc.

     Correct all of the errors in the project before continuing.

5. Update Code

     VB.Net 2008 continues to support many VB6 methods.  HOWEVER, they are actually SLOWER than their
     VB.NET counterparts, so it is very important to go through each line of code in your project, and replace
     each VB6 method with it's .NET counterpart.

     VB6 code runs good in VB6, but VB6 code in VB.NET runs bad (very bad).  VB.NET code in VB.NET runs
     good (VERY good), much faster than VB6 code runs in VB6 (if that makes sense).

     So here are some examples of how to replace VB6 methods with VB.NET counterparts:

         'TIP:  VB.Net strings are zero based, in other words, the first position of a string is 0.  In VB6, the
                 first position was 1.  This greatly affects how strings are parsed.

         Dim myString As String = "Go ahead and search for this string"

          -  Instr - Instead of using the Instr() method to search a string, use the IndexOf() method.

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

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

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

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

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

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

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

          -  Replace the "And" operator with "AndAlso", replace the "Or" operator with "OrElse".
             Do this in any non-bitwise comparison.

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

               Or Old way:  If 1 = 1 Or 2 = 2 Or 3 = 3 Then
               Or New way:  If 1 = 1 OrElse 2 = 2 OrElse 3 = 3 Then

          -  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 Unil EOF(1)
                    instring = LineInput(1)  'Read 1 line from a file

               ** VB.Net File I/O:
               Dim reader As New System.IO.StreamReader(myF ile)
               Do Until reader.EndOfStream = True
                    instring = reader.ReadLine()

6. DoEvents

     As soon as I upgraded processor intensive VB6 applications to VB.NET, I noticed that the performance
     was terrible!  While code upgrades are contributing factors, DoEvents is one of the biggest culprits!  VB6
     applications ran (in some cases) about 10 times slower when they were upgraded to VB.NET.  With a
     few tweaks, VB.NET application performance can be greatly improved, so that they run about 40% -
     50% FASTER than VB6...  

     1.  Add a Module to your project, and name it something like "Do_Events"

     2.  Insert the following code into the module you added:

          Module Do_Events

               Friend Declare Function SetThreadPriority Lib "kernel32" (ByVal hThread As Integer, _
                    ByVal nPriority As Integer) As Integer

               Friend Declare Function SetPriorityClass Lib "kernel32" (ByVal hProcess As Integer, _
                    ByVal dwPriorityClass As Integer) As Integer

               Friend Declare Function GetCurrentThread Lib "kernel32" () As Integer
               Friend Declare Function GetCurrentProcess Lib "kernel32" () As Integer

               Friend Const THREAD_PRIORITY_HIGHEST As Short = 2
               Friend Const HIGH_PRIORITY_CLASS As Integer = &H80

          End Module

     3.  Add 2 lines of code before the intensive processing begins to set the thread priority:

          SetThreadPriority(GetCurre ntThread, THREAD_PRIORITY_HIGHEST)
          SetPriorityClass(GetCurren tProcess, HIGH_PRIORITY_CLASS)  

     4.  Use DoEvents() sparingly!  Calling DoEvents() has a big performance hit, so use it sparingly.

          Dim iLoops As Integer = 0
          Do Until iLoops = 10000

               'Calling DoEvents() every 500 loops will greatly increase application performance
               If iLoops Mod 500 = 0 Then DoEvents()

               iLoops += 1   'Add 1 to iLoops


     5.  Create a specific Sub routine for updating the controls on your Form, and call the Sub whenever you
          want to update the form.  

          In the example above, you can substitue DoEvents() with the name of your update method

          Private Sub UpdateForm()

               'Update all controls here:
               progressBar1.Value += 1        'Update ProgressBar
               label1.Text = "Processing..."   'Update Labels, TextBoxes, etc...

               Application.DoEvents()  'Call DoEvents() so the form can refresh the changes to the controls

          End Sub

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!  



Comments (2)

Hi VBRocks,

your upgrade article is very helpful, but I have doubts on one point. You are saying that the VB6 string funtions like InStr and Mid do not work fast in VB.NET. But I have found other articles in the Internet claiming that only the first call of the VB6 functions is slow while the following calls are (almost) as fast as the VB.NET functions. Can you confirm this, or did you get different results when you compared the functions?


I have noticed that when compared with Windows Forms in VB.NET (e.g., Visual Studio 2010) a lot of features are not available for WPF, and many users have said forget going down that path.  If you come into the VB.NET space with significant WPF abilities, then perhaps it's another story.  

There may also be many Windows Form issues in what you are converting from VB6 to VB.NET, so it may be better to stick with the Windows Form approach.  

As a specific example, developing a workflow GUI for task handling in which button, pictures can be connected with lines, moved, and right-clicked for command menus can be accomplished more straightforwardly using the ShapeContainer package tools in Windows Forms.   So, when the WPF seems like the logical choice for creating a GUI application for workflow and tasking, most experts have claimed that there are too many limitations with WPF.

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