Visual Basic 6's App object exposes a useful property named PrevInstance, which allows you to determine whether there are other instances of the same application running. This property has never been implemented in VB.NET, even though a VB2005 application can use the StartupNextInstance event for this purpose.

' to display this code, open the Application page of the My Project designer and click the Application Events button
Namespace My
   Partial Friend Class MyApplication
      Private Sub MyApplication_StartupNextInstance(ByVal sender As Object, ByVal e As Microsoft.VisualBasic.ApplicationServices.StartupNextInstanceEventArgs) Handles Me.StartupNextInstance
         ' another instance of this application has been launched
      End Sub
   End Class
End Namespace

Even though the book isn't specifically on the C# language, it adequately covers most of the new features of C# 2.0, such as generics, iterators, and anonymous methods.

Why a book on the BCL? Well, in these years I realized that far too many developers focus solely on high-level features - such as Windows Forms, ADO.NET, and ASP.NET - and often fail to leverage the full potential from other portions of the .NET Framework. For example, I have seen many apps that use verbose and unefficient validation rules that might be replaced by a single regular expression. Or apps that could be written in a fraction of time (and lines of code) if the author had been conscious of the full potential of reflection and custom attributes. Not to mention the fact that new .NET 2.0 features, such as generics, could make things only worse.

In general I find that most books that are "translated" from a different programming language are disappointing, so you might wonder why this book should be different. First, when I signed the contract for my VB 2005 book I already knew that the book would have been translated to C#, thus I planned the book so that its structure wouldn't be too VB-centric. Secoond, in the last four years I have been using C# in virtually all my programming projects - in fact I have surely written more C# code than VB code. For this reason, you'll find that the C# code is carefully optimized to use all the usual C#-specific techniques, such as iterators and anonymous delegates.

Shortly I will prepare a home page for the book on this site, with a couple of sample chapters. In the meantime, you can read more about the book (and hopefully order it) on Amazon's home page.

Yesterday I got an email from reader Claudio Fontana, with the following, deceiptively simple request: how can you avoid flickering while updating many controls on a form? The problem is especially serious when you need to add thousands of items to a ListView or a TreeView.

In VB6 this problem can be solved quite simply by temporarily setting the Visible (or Enabled) property to False for all the controls about to be updated: the control isn't actually hidden, yet the result of the update operation appears istantaneously when the property is reset to True. Just as interesting: the update operation is carried out much faster if the control is invisible, often twice as faster. Alas, this trick doesn't work in .NET, because as soon as you set the Visible property to False the control is immediately hidden. It's necessary to find another solution.

A few Windows Forms controls - namely the ListBox, ComboBox, ListView, and TreeView controls - do expose the BeginUpdate and EndUpdate methods, which allow you to "freeze" the control while you add items to it. Not only do they solve the flickering problem, they also speed up the update operation, tipically by a factor of 2.5x. However, if your form contains many controls that do NOT expose these methods, you must devise something else, and this was exactly the problem that Claudio submitted, after he unsuccessfully googled around on the 'Net looking for a solution.

The problem is quite intriguing, thus I decided to spend some time on it, until I came to the following solution. The idea is simple, and can be split in the following steps: (1) take a snapshot of the current form's appearance, by making a pixel-by-pixel copy into a bitmap, (2) create a PictureBox control as large as the form, and load the bitmap into the PictureBox, (3) add the PictureBox to the form's Controls collection and bring the PictureBox in front of all other controls, (4) while the user looks at the "frozen" image of the form, update your controls, using the BeginUpdate/EndUpdate mthods if possible to speed up execution, (5) when the update operation is completed, remove the PictureBox from the Controls collection, so that the user can now see the real form.

You just need one dozen statements to implement this algorithim, but I prepared a class to make the code more reusable and to ensure that it releases all resources correctly:

Public Class FormFreezer
   Implements IDisposable

   ' The form being frozen
   Dim Form As Form
   ' the auxiliary PictureBox that will cover the form
   Dim PictureBox As PictureBox
   ' the number of times the Freeze method has been called
   Dim FreezeCount As Integer = 0

   ' create an instance associated with a given form
   ' and optionally freeze the form right away
   Public Sub New(ByVal form As Form, Optional ByVal freezeIt As Boolean = False)
      Me.Form = form
      If freezeIt Then Me.Freeze()
   End Sub

   ' freeze the form 
   Public Sub Freeze()
      ' Remember we have frozen the form once more
      FreezeCount += 1
      ' Do nothing if it was already frozen
      If FreezeCount > 1 Then Exit Sub

      ' Create a PictureBox that resizes with its contents
      PictureBox = New PictureBox()
      PictureBox.SizeMode = PictureBoxSizeMode.AutoSize
      ' create a bitmap as large as the form's client area and with same color depth
      Dim frmGraphics As Graphics = Form.CreateGraphics()
      Dim rect As Rectangle = Form.ClientRectangle
      PictureBox.Image = New Bitmap(rect.Width, rect.Height, frmGraphics)
      frmGraphics.Dispose()

      ' copy the screen contents, from the form's client area to the hidden bitmap
      Dim picGraphics As Graphics = Graphics.FromImage(PictureBox.Image)
      picGraphics.CopyFromScreen(Form.PointToScreen(New Point(rect.Left, rect.Top)), New Point(0, 0), New Size(rect.Width, rect.Height))
      picGraphics.Dispose()

      ' Display the bitmap in the picture box, and show the picture box in front of all other controls
      Form.Controls.Add(PictureBox)
      PictureBox.BringToFront()
   End Sub

   ' unfreeze the form
   ' Note: calls to Freeze and Unfreeze must be balanced, unless force=true 
   Public Sub Unfreeze(Optional ByVal force As Boolean = False)
      ' exit if nothing to unfreeze
      If FreezeCount = 0 Then Exit Sub
      ' remember we've unfrozen the form, but exit if it is still frozen
      FreezeCount -= 1
      ' force the unfreeze if so required
      If force Then FreezeCount = 0
      If FreezeCount > 0 Then Exit Sub

      ' remove the picture box control and clean up
      Form.Controls.Remove(PictureBox)
      PictureBox.Dispose()
      PictureBox = Nothing
   End Sub

   ' return true if the form is currently frozen
   Public ReadOnly Property IsFrozen() As Boolean
      Get
         Return FreezeCount > 0
      End Get
   End Property

   ' ensure that resources are cleaned up correctly
   Public Overridable Sub Dispose() Implements IDisposable.Dispose
      Me.Unfreeze(True)
   End Sub
End Class

This is the C# version, translated from VB by Claudio:

Using the FormFreezer class is quite simple. Here's a code sample, which assumes that it is located inside a form class so that the Me keyword points to the current form:

   Dim ff As New FormFreezer(Me, True)
   ' update controls here
   ' ...
   ff.Unfreeze()

Many, if not most, Windows Forms samples you can find on the 'net include one or more calls to unmanaged code in Windows DLLs, often in the form of calls to the SendMessage API methods to fix some of the (very few) missing features of .NET controls. The problem is, such a call to unmanaged code creates a problem when the program runs as a ClickOnce application, because it requires higher CAS privileges.

Even though this problem doesn't have a generic solution, when you just need to send a message to the control you are inheriting from, you can avoid an explicit call to SendMessage by invoking the protected DefWndProc method instead. For example, let's say that you are writing an enhanced ComboBox that exposes the TopIndex property, which can set or return the index of the first visible item in the list area. These two operations can be implemented by sending the control the CB_SETTOPINDEX or CB_GETTOPINDEX message, respectively. Here's how you can use the DefWndProc method instead of SendMessage:

Public Class ComboBoxEx
   Inherits System.Windows.Forms.ComboBox

   Public Property TopIndex() As Integer
      Get
         Const CB_GETTOPINDEX As Int32 = &H15B
         Dim m As New Message()
         m.HWnd = Me.Handle
         m.Msg = CB_GETTOPINDEX
         Me.DefWndProc(m)
         Return m.Result.ToInt32()
      End Get
      Set(ByVal value As Integer)
         Const CB_SETTOPINDEX As Int32 = &H15C
         Dim m As New Message()
         m.HWnd = Me.Handle
         m.Msg = CB_SETTOPINDEX
         m.WParam = New IntPtr(value)
         Me.DefWndProc(m)
      End Set
   End Property

End Class

MsgHookX is an ActiveX DLL that allows VB6 developers to perform safe and efficient intra-applicaton subclassing. (In this context, intra-application sublclassing means that you can intercept any message that Windows sends to a window or a control in the current application, as opposed to a window created by another application, a much more difficult task.) I wrote this DLL many years ago, when VB5 was released, and mentioned it in several books and magazine articles. I made the DLL available on the vb2themax site, but I omitted to upload the DLL in this new, .NET-only site.

Well, given the many mails I continue to receive from readers, it seems that VB6 is still alive and in good shape, and many VB6 developers continune to happily subclass their controls. For this reason I decided to make the DLL available again on this site. Here's a summary of what it does:

• safe subclassing: can be used within the IDE and in break mode without any risk of system crashes.
• it provides the BeforeMessage and AfterMessage events for easy event-driven programming model
• it additionally can notify incoming messages through the IMsgHookEvents secondary interface, for better performance and easier debugging (in some cases, events are inhibited in the IDE)
• highest flexibility: you can decide to call the original window procedure yourself from within the BeforeMessage event/method and/or cancel the default processing for the message. You can also browse and modify the value that will be returned to the operating system.
• the DLL's type library includes the definition of over 300 symbolic constants that define the most common Windows messages, so you don't have to use the API Viewer to include them in your applications.

Have fun with it, but - please, please! - turn to VB.NET as soon as you can, if you haven't yet.

I am working at the migration of a large VB6 project and at one point I needed to drop a few methods in the VB6 app, in such a way that the methods would be "invisible" to VB.NET. This action was necessary because these methods performed similarly to a .NET native method. Obviously, I had the option to manually delete the methods after the migration, but if their number is high and if you need to run the wizard more than once on the same VB6 app (as it happens frequently, in the process of preparing the app for the migration), then deleing these portions of code each time becomes a nuisance.

Apparently, you can't instruct the migration wizard to ignore one or more pieces of code. Nevertheless, the solution is quite simple: you just need to bracket these pieces of code - entire methods or just individual statements - in a #If Win32 ...#End If block. The Win32 compilation constant - that is probably ignored by most VB developers today - was introduced when Visual Basic 4 was released, and was recognized also by VB5 and VB6 (but not by any version of VB.NET). Visual Basic 4 is the only version of this language that is available in 16-bit and 32-bit edition, and this compilation constant (together with Win16) allowed to define blocks of code that were compiled under only one of those versions, while allowing to mantain a single source code for both. Therefore, the following VB6 code:

#If WIN32 Then
   Private Sub Do Something(ByVal n As Integer)   
      ' ...
   End Sub
#End If

is correctly migrated to VB.NET by the migration wizard as follows:

#If WIN32 Then
   Private Sub DoSomething(ByVal n As Short)
      ' ...
   End Sub
#End If

I am reorganizing my MP3 collection and found that I needed to rename a large quantity of files. Of course, there are many free utilities that allow this operation - and that can use MP3 tags in the process - but I thought that I might write one myself. Thanks to regular expressions, the task shouldn't be that hard. In fact, in a few minutes I came up with the following console application. As you see, most of the code is used to extract and validate arguments on the command line:

Imports System.Text.RegularExpressions
Imports System.IO

Module Renx

   Function Main(ByVal args() As String) As Integer
      Console.WriteLine("RENX (C) Francesco Balena / Code Architects Srl")

      Dim recurse As Boolean = False
      Dim renameMode As Boolean = False
      Dim oldNamePattern As String = Nothing
      Dim newNamePattern As String = Nothing

      ' analyze each argument
      For Each arg As String In args
         Select Case arg.ToLower()
            Case "/s", "-s"
               recurse = True
            Case "/r", "-r"
               renameMode = True
            Case "/h", "-h"
               Return ShowHelp(0)
            Case Else
               If oldNamePattern Is Nothing Then
                  oldNamePattern = "^" & arg & "$"
               ElseIf newNamePattern Is Nothing Then
                  newNamePattern = arg
               Else
                  Return ShowHelp(1)
               End If
         End Select
      Next

      ' check that we have both mandatory arguments
      If oldNamePattern Is Nothing OrElse newNamePattern Is Nothing Then
         Return ShowHelp(1)
      End If
      ' create the regex and check that pattern syntax is ok
      Dim reSearch As Regex
      Try
         reSearch = New Regex(oldNamePattern, RegexOptions.IgnoreCase)
         ' test the replace pattern as well
         Dim tmp As String = reSearch.Replace("a dummy string", newNamePattern)
      Catch ex As Exception
         Console.WriteLine("SYNTAX ERROR: {0}", ex.Message)
         Return 3
      End Try
      Console.WriteLine()

      ' iterate over all files in current directory (and its subdirectories, if recurse mode)
      Dim searchOpt As SearchOption = SearchOption.TopDirectoryOnly
      If recurse Then searchOpt = SearchOption.AllDirectories

      Dim parsedFilesCount As Integer = 0
      Dim renamedFilesCount As Integer = 0
      Dim errorsCount As Integer = 0
      For Each oldFile As String In Directory.GetFiles(Directory.GetCurrentDirectory(), "*.*", searchOpt)
         parsedFilesCount += 1
         ' the regex applies to name only
         Dim oldName As String = Path.GetFileName(oldFile)
         Dim ma As Match = reSearch.Match(oldName)
         If ma.Success Then
            ' this is the new name
            Dim newName As String = ma.Result(newNamePattern)
            Console.WriteLine(oldFile)
            Console.Write(" => {0}", newName)
            renamedFilesCount += 1
            ' proceed with rename only if not in simulation mode
            If renameMode Then
               Try
                  Dim dirName As String = Path.GetDirectoryName(oldFile)
                  Dim newFile As String = Path.Combine(dirName, newName)
                  File.Move(oldFile, newFile)
               Catch ex As Exception
                  Console.Write(" -- ERROR: {0}", ex.Message)
                  errorsCount += 1
               End Try
            End If
            Console.WriteLine()
         End If
      Next

      ' Display a report
      If renameMode Then
         Console.WriteLine("Summary: {0} parsed files, {1} renamed files, {2} errors", parsedFilesCount, renamedFilesCount, errorsCount)
      Else
         Console.WriteLine("Summary: {0} parsed files, {1} files affected", parsedFilesCount, renamedFilesCount)
         Console.WriteLine()
         Console.WriteLine("NOTE: Running in simulation mode. Specify the /R option to actually rename files.")
      End If
      ' Return an error code
      If errorsCount = 0 Then
         Return 0
      Else
         Return 2
      End If
   End Function

   Function ShowHelp(ByVal exitCode As Integer) As Integer
      Console.WriteLine()
      Console.WriteLine("Syntax: RENX <oldnamepattern> <newnamepattern> [/R] [/S] [/H]")
      Console.WriteLine(" oldnamepattern : regex that selects the files to be renamed")
      Console.WriteLine(" newnamepattern : regex that specifies how files must be renamed")
      Console.WriteLine(" /R : rename files")
      Console.WriteLine(" /S : iterate over subdirectories")
      Console.WriteLine(" /H : display this help")
      Console.WriteLine("NOTE: By default the program runs in simulation mode, and just displays how files would be renamed.")
      Console.WriteLine(" You must specify the /R option to actually rename the files.")
      Return exitCode
   End Function

End Module

At the very minimum, the RENX utility requires two arguments: a regex that specifies which files in the current directory (and its subdirectories, if you add the /S option) must be renamed, and a second regex that specifies how to rename the files that are matched by the first regex. The power of RENX is the fact that the first regex can (actually, must) specify one or more groups of characters, and these groups are then referenced in the second regex. For example, let's suppose that I have a folder with the following files:

        01 Speak to Me.mp3
        02 On the Run.mp3
        03 Time.mp3
        04 The Great Gig in the Sky.vb3
        05 Money.mp3
        06 Us and Them.mp3
        07 Any Colour You Like.vbr
        08 Brain Damage.mp3
        09 Eclipse.vb3

and that I want to rename them as follows:

        01 - Speak to Me - The Dark Side of the Moon.mp3
        02 - On the Run - The Dark Side of the Moon.mp3
        03 - Time - The Dark Side of the Moon.mp3
        04 - The Great Gig in the Sky - The Dark Side of the Moon.vbr
        05 - Money - The Dark Side of the Moon.mp3
        06 - Us and Them - The Dark Side of the Moon.mp3
        07 - Any Colour You Like - The Dark Side of the Moon.vb3
        08 - Brain Damage - The Dark Side of the Moon.mp3
        09 - Eclipse - The Dark Side of the Moon.vbr

Here's the RENX command that does it:

        RENX "(\d\d) (.+?)(\..+)"    "${1} - ${2} - The Dark Side of the Moon.${3}"

Notice that the first regex creates three groups by enclosing them in parenthesis: (\d\d) matches the song number, (.+?) matches the song title, and (\..+) matches the file extension, dot included. The second argument can then reorder these three groups, using the ${N}, where N is the position of the group as specified in the first regex. It is therefore to insert a dash after the song number, and the albumname after the song title.

Because the RENX utility is quite dangerous, by default it doe NOT rename the files, and it just lists how files would be renamed. To actually proceed with the rename operation, you must specify the /R option:

        RENX "(\d\d) (.+?)(\..+)"    "${1} - ${2} - The Dark Side of the Moon${3}" /R

That's all. You can play with the source code to extend the RENX utility as you prefer, and maybe turn it into a Windows Form application, or you can download the binary version from this link: Renx.zip (5.51 KB)

A few minutes ago I made all the code samples for Programming Microsoft Visual Basic 2005: The Language available on the book home page. It's a 7.5M download that contains several thousand lines of carefully crafted, optimized, reusable source code, including the following:

• a VB class that works with fractions
• a base form for simplified data entry
• a class to cache text files
• several custom iterators for better For Each loops
• tons of examples with generics
• two expression evaluators, the former built on regexes, the latter implemented via on-the-fly compilation
• a utility to display project statistics (a demo for regexes)
• a RegexTester stand-alone utility, to help you build, test and compile regular expressions
• an example of custom provider for My.Settings
• an example of how you can intercept ANY event from ANY set of Windows Forms controls
• attribute-based benchmarks
• a complete infrastructure for writing Windows Forms plug-ins
• an attribute-based library to write data-centric N-tier applications
• several Visual Studio macros
• Visual Studio visualizers for files, regex, and images
• .... and a lot more

On the same page you can also find an errata document for typos and mistakes found after the book went to print.

Enjoy the code (and buy the book if you like it! )

The longer I work with generics, the more I like them, and I continue to discover new ways to simplify my code by using them. More specifically, I like the ability to write type-safe code that is also more concise, efficient, and (above all) readable, because I don't have to use tons of CType and DirectCast operators. Today I gathered the generic methods I use more frequently in the following module. They are tiny and simple, yet they save me a lot of time and code.

Module GenericFunctions

   ' Swap two variables
   Public Sub Swap(Of T)(ByRef var1 As T, ByRef var2 As T)
      Dim tmp As T = var1
      var1 = var2
      var2 = tmp
   End Sub

   ' Type-safe version of the IIF function
   ' returns valueOnTrue if expression is True, else returns valueOnFalse
   Public Function IIf(Of T)(ByVal expression As Boolean, ByVal valueOnTrue As T, ByVal valueOnFalse As T) As T
      If expression Then
         Return valueOnTrue
      Else
         Return valueOnFalse
      End If
   End <