VB.NET: Syntax Highlighting in a RichTextBox control

This last weekend I expirimented a little bit with extending the functionality of the RichTextBox control. Below you'll find an example of a small class that enherits from the RichTextBox control and allows you to implement syntax highlighting (with the use of a couple Win32 API call to smooth over the process of course.) The code pretty much speaks for itself.

PublicClass SyntaxRTB

   Inherits System.Windows.Forms.RichTextBox

   PrivateDeclareFunction SendMessage Lib "user32" Alias "SendMessageA" _
      (ByVal hWnd As IntPtr, ByVal wMsg AsInteger, ByVal wParam AsInteger, ByVal lParam AsInteger) AsInteger

   PrivateDeclareFunction LockWindowUpdate Lib "user32" (ByVal hWnd AsInteger) AsInteger

   Private _SyntaxHighlight_CaseSensitive AsBoolean = False

   Private Words AsNew DataTable

   'Contains Windows Messages for the SendMessage API call
   PrivateEnum EditMessages
      LineIndex = 187
      LineFromChar = 201
      GetFirstVisibleLine = 206
      CharFromPos = 215
      PosFromChar = 1062
   EndEnum

   ProtectedOverridesSub OnTextChanged(ByVal e As System.EventArgs)
      ColorVisibleLines()
   EndSub

   PublicSub ColorRtb()
      Dim FirstVisibleChar AsInteger
      Dim i AsInteger = 0

      While i < Me.Lines.Length
         FirstVisibleChar = GetCharFromLineIndex(i)
         ColorLineNumber(i, FirstVisibleChar)
         i += 1
      EndWhile
   EndSub

   PublicSub ColorVisibleLines()
      Dim FirstLine AsInteger = FirstVisibleLine()
      Dim LastLine AsInteger = LastVisibleLine()
      Dim FirstVisibleChar AsInteger

      If (FirstLine = 0) And (LastLine = 0) Then
         'If there is no text it will error, so exit the sub
         ExitSub
      Else
         While FirstLine < LastLine
            FirstVisibleChar = GetCharFromLineIndex(FirstLine)
            ColorLineNumber(FirstLine, FirstVisibleChar)
            FirstLine += 1
         EndWhile
      EndIf

   EndSub

   PublicSub ColorLineNumber(ByVal LineIndex AsInteger, ByVal lStart AsInteger)
      Dim i AsInteger = 0
      Dim Instance AsInteger
      Dim LeadingChar, TrailingChar AsString
      Dim SelectionAt AsInteger = Me.SelectionStart
      Dim MyRow As DataRow
      Dim Line() AsString, MyI AsInteger, MyStr AsString

      ' Lock the update
      LockWindowUpdate(Me.Handle.ToInt32)

      MyI = lStart

      If CaseSensitive Then
         Line = Split(Me.Lines(LineIndex).ToString, " ")
      Else
         Line = Split(Me.Lines(LineIndex).ToLower, " ")
      EndIf

      ForEach MyStr In Line
         Me.SelectionStart = MyI
         Me.SelectionLength = MyStr.Length

         If Words.Rows.Contains(MyStr) Then
            MyRow = Words.Rows.Find(MyStr)
            If (Not CaseSensitive) Or (CaseSensitive And MyRow("Word") = MyStr) Then
               Me.SelectionColor = Color.FromName(MyRow("Color"))
            EndIf
         Else
            Me.SelectionColor = Color.Black
         EndIf

         MyI += MyStr.Length + 1
      Next

      ' Restore the selectionstart
      Me.SelectionStart = SelectionAt
      Me.SelectionLength = 0
      Me.SelectionColor = Color.Black

      ' Unlock the update
      LockWindowUpdate(0)
   EndSub

   PublicFunction GetCharFromLineIndex(ByVal LineIndex AsInteger) AsInteger
      Return SendMessage(Me.Handle, EditMessages.LineIndex, LineIndex, 0)
   EndFunction

   PublicFunction FirstVisibleLine() AsInteger
      Return SendMessage(Me.Handle, EditMessages.GetFirstVisibleLine, 0, 0)
   EndFunction

   PublicFunction LastVisibleLine() AsInteger
      Dim LastLine AsInteger = FirstVisibleLine() + (Me.Height / Me.Font.Height)

      If LastLine > Me.Lines.Length Or LastLine = 0 Then
         LastLine = Me.Lines.Length
      EndIf

      Return LastLine
   EndFunction

   PublicSubNew()
      Dim MyRow As DataRow
      Dim arrKeyWords() AsString, strKW AsString

      Me.AcceptsTab = True

      ''Load all the keywords and the colors to make them 
      Words.Columns.Add("Word")
      Words.PrimaryKey = New DataColumn() {Words.Columns(0)}
      Words.Columns.Add("Color")

      arrKeyWords = NewString() {"select", "insert", "delete", _
         "truncate", "from", "where", "into", "inner", "update", _
         "outer", "on", "is", "declare", "set", "use", "values", "as", _
         "order", "by", "drop", "view", "go", "trigger", "cube", _
         "binary", "varbinary", "image", "char", "varchar", "text", _
         "datetime", "smalldatetime", "decimal", "numeric", "float", _
         "real", "bigint", "int", "smallint", "tinyint", "money", _
         "smallmoney", "bit", "cursor", "timestamp", "uniqueidentifier", _
         "sql_variant", "table", "nchar", "nvarchar", "ntext", "left", _
         "right", "like","and","all","in","null","join","not","or"}

      ForEach strKW In arrKeyWords
         MyRow = Words.NewRow()
         MyRow("Word") = strKW
         MyRow("Color") = Color.LightCoral.Name
         Words.Rows.Add(MyRow)
      Next

   EndSub

   PublicProperty CaseSensitive() AsBoolean
      Get
         Return _SyntaxHighlight_CaseSensitive
      EndGet
      Set(ByVal Value AsBoolean)
         _SyntaxHighlight_CaseSensitive = Value
      EndSet
   EndProperty

EndClass   

Update July 8th, 2008: Here's a link that shows a couple tips that may help in writing your own Syntax Highlighting RichTextBox control:

http://codebetter.com/blogs/patricksmacchia/archive/2008/07/07/some-richtextbox-tricks.aspx