Chris Pietschmann

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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.

 

Public Class SyntaxRTB

   Inherits System.Windows.Forms.RichTextBox

   Private
Declare Function SendMessage Lib "user32" Alias "SendMessageA" _
      
(ByVal hWnd As IntPtr, ByVal wMsg As Integer, ByVal wParam As Integer, ByVal lParam As Integer) As Integer

 

 

   Private Declare Function LockWindowUpdate Lib "user32" (ByVal hWnd As Integer) As Integer

   Private _SyntaxHighlight_CaseSensitive As Boolean = False

   Private Words As New DataTable

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

 

   Protected Overrides Sub OnTextChanged(ByVal e As System.EventArgs)
      
ColorVisibleLines()
   
End Sub

 

   Public Sub ColorRtb()
      
Dim FirstVisibleChar As Integer
      
Dim i As Integer = 0

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

 

   Public Sub ColorVisibleLines()
      
Dim FirstLine As Integer = FirstVisibleLine()
      Dim LastLine As Integer = LastVisibleLine()
      Dim FirstVisibleChar As Integer

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

   
End Sub

 

   Public Sub ColorLineNumber(ByVal LineIndex As Integer, ByVal lStart As Integer)
      
Dim i As Integer = 0
      
Dim Instance As Integer
      
Dim LeadingChar, TrailingChar As String
      
Dim SelectionAt As Integer = Me.SelectionStart
      
Dim MyRow As DataRow
      
Dim Line() As String, MyI As Integer, MyStr As String

      
' 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, " ")
      
End If

      
For Each 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"))
            
End If
         Else
            
Me.SelectionColor = Color.Black
         
End If

         
MyI += MyStr.Length + 1
      Next

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

      
' Unlock the update
      
LockWindowUpdate(0)
   
End Sub

 

   Public Function GetCharFromLineIndex(ByVal LineIndex As Integer) As Integer
      
Return SendMessage(Me.Handle, EditMessages.LineIndex, LineIndex, 0)
   
End Function

 

   Public Function FirstVisibleLine() As Integer
      
Return SendMessage(Me.Handle, EditMessages.GetFirstVisibleLine, 0, 0)
   
End Function

 

   Public Function LastVisibleLine() As Integer
      
Dim LastLine As Integer = FirstVisibleLine() + (Me.Height / Me.Font.Height)

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

      
Return LastLine
   
End Function

 

   Public Sub New()
      
Dim MyRow As DataRow
      
Dim arrKeyWords() As String, strKW As String

      
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 =
New String() {"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"}

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

   
End Sub

 

   Public Property CaseSensitive() As Boolean
      
Get
         
Return _SyntaxHighlight_CaseSensitive
      
End Get
      
Set(ByVal Value As Boolean)
         _SyntaxHighlight_CaseSensitive = Value
      
End Set
   End Property

 

 

End Class   

 

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

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