引用Wayne's帖子，这里是有关code。它使用GDI绘制行号旁边的文本框。

Referencing Wayne's post, here is the relevant code. It is using GDI to draw line numbers next to the text box.

Public Sub New()
    MyBase.New()

    'This call is required by the Windows Form Designer.
    InitializeComponent()

    'Add any initialization after the InitializeComponent() call
    SetStyle(ControlStyles.UserPaint, True)
    SetStyle(ControlStyles.AllPaintingInWmPaint, True)
    SetStyle(ControlStyles.DoubleBuffer, True)
    SetStyle(ControlStyles.ResizeRedraw, True)
End Sub

Private Sub RichTextBox1_SelectionChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles RichTextBox1.SelectionChanged
    FindLine()
    Invalidate()
End Sub

Private Sub FindLine()
    Dim intChar As Integer

    intChar = RichTextBox1.GetCharIndexFromPosition(New Point(0, 0))
    intLine = RichTextBox1.GetLineFromCharIndex(intChar)
End Sub

Private Sub DrawLines(ByVal g As Graphics, ByVal intLine As Integer)
    Dim intCounter As Integer, intY As Integer

    g.Clear(Color.Black)

    intCounter = intLine + 1
    intY = 2
    Do
        g.DrawString(intCounter.ToString(), Font, Brushes.White, 3, intY)
        intCounter += 1

        intY += Font.Height + 1
        If intY > ClientRectangle.Height - 15 Then Exit Do
    Loop
End Sub

Protected Overrides Sub OnPaint(ByVal e As System.Windows.Forms.PaintEventArgs)
    DrawLines(e.Graphics, intLine)
End Sub

Private Sub RichTextBox1_VScroll(ByVal sender As Object, ByVal e As System.EventArgs) Handles RichTextBox1.VScroll
    FindLine()
    Invalidate()
End Sub

Private Sub RichTextBox1_UserScroll() Handles RichTextBox1.UserScroll
    FindLine()
    Invalidate()
End Sub

RichTextBox的是像这样覆盖：

The RichTextBox is overridden like this:

Public Class UserControl1
Inherits System.Windows.Forms.RichTextBox

Public Event UserScroll()

Protected Overrides Sub WndProc(ByRef m As System.Windows.Forms.Message)
    If m.Msg = &H115 Then
        RaiseEvent UserScroll()
    End If

    MyBase.WndProc(m)
End Sub
End Class

（code。通过divil在xtremedotnettalk.com论坛。）

(Code by divil on the xtremedotnettalk.com forum.)