This article demonstrates how to add line numbers to a rich text box control. This is done by adding a picture box control on the left side of the rich text box control. When the appropriate events happen on the Form or on the RichTextBox control we call a method that paints the line numbers on the PictureBox control. This approach is more accurate and efficient than other approaches I’ve seen where another textbox control was used for printing the line numbers. The PictureBox will only print the line numbers that are currently visible in the RichTextBox control.
During the process of constructing this code sample, I initially based it on the code sample provided in the article http://www.codeproject.com/cs/miscctrl/numberedtextbox.asp and enhanced it by doing the following:
- Replace the Label control for numbering with a PictureBox
- I fixed the scrolling problem with that implementation due to the fact that RichTextBox uses smooth scrolling (scrolling with the scrollbar scrolls the text in pixels, not in lines), as a result sometimes the first line may be displayed in half, at which case the line numbering should address it.
Here is the code for printing the line numbers. Note that we have a RichTextBox control
called MyRichTextBox and a PictureBox control called MyPictureBox. The method gets one
argument which is the Graphics of the PictureBox control.
This is the method DrawRichTextBoxLineNumbers:
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Private Sub DrawRichTextBoxLineNumbers(ByRef g As Graphics)
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'Calculate font heigth as the difference in Y coordinate
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'between line 2 and line 1
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'Note that the RichTextBox text must have at least two lines.
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' So the initial Text property of the RichTextBox
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' should not be an empty string. It could be something
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' like vbcrlf & vbcrlf & vbcrlf
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With MyRichTextBox
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Dim font_height As Single
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font_height = .GetPositionFromCharIndex(.GetFirstCharIndexFromLine(2)).Y _
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- .GetPositionFromCharIndex(.GetFirstCharIndexFromLine(1)).Y
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If font_height = 0 Then Exit Sub
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'Get the first line index and location
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Dim first_index As Integer
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Dim first_line As Integer
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Dim first_line_y As Integer
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first_index = .GetCharIndexFromPosition(New _
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Point(0, g.VisibleClipBounds.Y + font_height / 3))
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first_line = .GetLineFromCharIndex(first_index)
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first_line_y = .GetPositionFromCharIndex(first_index).Y
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'Print on the PictureBox the visible line numbers of the RichTextBox
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g.Clear(Control.DefaultBackColor)
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Dim i As Integer = first_line
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Dim y As Single
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Do While y < g.VisibleClipBounds.Y + g.VisibleClipBounds.Height
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y = first_line_y + 2 + font_height * (i - first_line - 1)
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g.DrawString((i).ToString, .Font, Brushes.DarkBlue, MyPictureBox.Width _
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- g.MeasureString((i).ToString, .Font).Width, y)
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i += 1
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Loop
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'Debug.WriteLine("Finished: " & firstLine + 1 & " " & i – 1)
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End With
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End Sub
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Private Sub r_Resize(ByVal sender As Object, ByVal e As System.EventArgs) _Handles MyRichTextBox.Resize
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DrawRichTextBoxLineNumbers(Me.MyPictureBox.CreateGraphics)
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MyPictureBox.Invalidate()
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End Sub
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Private Sub r_VScroll(ByVal sender As Object, ByVal e As System.EventArgs) _
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Handles MyRichTextBox.VScroll
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DrawRichTextBoxLineNumbers(Me.MyPictureBox.CreateGraphics)
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MyPictureBox.Invalidate()
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End Sub
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Private Sub p_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) _
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Handles MyPictureBox.Paint
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DrawRichTextBoxLineNumbers(e.Graphics)
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End Sub
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Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) _
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Handles MyBase.Load
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MyRichTextBox.Text = vbCrLf & vbCrLf & vbCrLf
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End Sub
Source: Line Numbering of RichTextBox in .NET 2.0