Creating Line Numbers for RichTextBox in C#

Pritam Zope

25 Comments

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ridtichai borseen4y ago
Thank you for the code. it worked for me
Cedric Ouellet4y ago
*FIX* Initially it won't work, and will keep adding everytime. This is because you need to do LineNumberTextBox.Clear(); at the beginning of AddLineNumbers(). Then, it will re-render line numbers and work as intended.
- Cedric Ouellet4y ago
  Also in richTextBox1_TextChanged, removed if statement, simply call AddLineNumbers() so that it refreshes all the time. For example: If i erase a line, I want it to disapear
Chand Bhandari5y ago
It is not working
Noman Ali5y ago
Not working tried almost 10 times
Yogi Grantz6y ago
This is awesome Pritam, I love it! it works great for me. John Fisher , to optimize the += just use Stringbuilder like this: StringBuilder sb = new StringBuilder(); for (int i = First_Line; i <= Last_Line + 2; i++) { sb.AppendLine($"{i + 1}."); } rtbLineNumber.Text += sb.ToString(); The whole thing works for me
- Yogi Grantz6y ago
  Sorry it should be just rtbLineNumber.Text = sb.ToString();
Sushma M7y ago
Thank you for the code. I understand well and it also worked perfectly :)
Carl Haney7y ago
This s crap the Linenumberbox don't add number as you goto next line...try doing a video tutorial on how to do this and we'll see if it works visually !
John Fisher7y ago
I mean, thanks though for posting but I can't spend any more time trying to get this to work,... sigh ...
John Fisher7y ago
For (int i = First_Line; i <= Last_Line + 2; i++) { LineNumberTextBox.Text += i + 1 + "\n"; }
John Fisher7y ago
Having hard time getting this to work ... you have bug ... this loop creates a super long string just tacking on the line number ...
Jayesh Betala7y ago
Need help regarding the code. only numbers from 1-3 is being displayed. Even after i press i enter the code isn't working. i tried atleast 3-4 times and made sure i made no error in following the steps above
- Chand Bhandari5y ago
  Same as you
Lord Chariot8y ago
I'm sorry, but I cannot find any reference to the object LineNumberTextBox above. Where/what is it?
- Pritam Zope8y ago
  LineNumberTextBox is the name of the RichTextBox, added on the left side of a form to display line numbers
Johnny Bravo8y ago
Hey how about LineNumberTextBox?
- Pritam Zope8y ago
  What about it ?
Tim Severance8y ago
Hi, Thanks for the great information, this is exactly what I have been searching for! Question: you don't mention setting up and adding the LineNumberTextbox. How do I set that up and add it to the form since the richtextbox1 is already filling the form? Thanks!Tim
- Tim Severance8y ago
  Sorry, after reading in more detail I see you explain it. It works great, thanks so much for the information!
Jill Bustillo10y ago
hello, i have a problem. the output when i tried the code is that it does not display the line numbers. how can i solve this?
- Jill Bustillo10y ago
  It already worked. thank you for your hard work :) i was wondering if i could modify it so that it for example i have a text that occupies lines 1 and 2, but since i didnt press enter it should only be counted as line number1, even though it occupies 2 spaces?
- Pritam Zope10y ago
  Did you perform above all steps correctly ? because above code is working perfectly without any error................
Pritam Zope10y ago
Thanks...
Santhakumar Munuswamy10y ago
Thanks for nice share

code

I am using AddLineNumbers() function to call anywhere in the program.

I am also using the getWidth() function that returns the specific width according to number of lines for auto resizing the line numbers width.

Here's code of AddLineNumbers() function:

public void AddLineNumbers()
{
// create & set Point pt to (0,0)
Point pt = new Point(0, 0);
// get First Index & First Line from richTextBox1
int First_Index = richTextBox1.GetCharIndexFromPosition(pt);
int First_Line = richTextBox1.GetLineFromCharIndex(First_Index);
// set X & Y coordinates of Point pt to ClientRectangle Width & Height respectively
pt.X = ClientRectangle.Width;
pt.Y = ClientRectangle.Height;
// get Last Index & Last Line from richTextBox1
int Last_Index = richTextBox1.GetCharIndexFromPosition(pt);
int Last_Line = richTextBox1.GetLineFromCharIndex(Last_Index);
// set Center alignment to LineNumberTextBox
LineNumberTextBox.SelectionAlignment = HorizontalAlignment.Center;
// set LineNumberTextBox text to null & width to getWidth() function value
LineNumberTextBox.Text = "";
LineNumberTextBox.Width = getWidth();
// now add each line number to LineNumberTextBox upto last line
for (int i = First_Line; i <= Last_Line + 2; i++)
{
LineNumberTextBox.Text += i + 1 + "\n";
}
}

Procedure

Step 1: Start Visual Studio & create new Windows Forms Application in C#.

Step 2: Drag & Drop RichTextBox onto Form1 & Set following properties to it.

Name	LineNumberTextBox
BackColor	White
BorderStyle	None
Cursor	PanNE
Dock	Left
ForeColor	Black
ReadOnly	true
ScrollBars	None

You can set BackColor & ForeColor to LineNumberTextBox as you wish.

Here you can also set Enabled property to false, but you can not see ForeColor & BackColor.

For ForeColor & BackColor we are set as above properties to LineNumberTextBox.

Step 3: Drag & Drop RichTextBox onto Form1 & Set Dock property to Fill. T he default name could be richTextBox1.

Step 4: Add above AddLineNumbers() function to your Form1 code or see Complete Code next.

Step 5: Add following events & code to Form1.

Load:
1. private void Form1_Load(object sender, EventArgs e)
2. {
3. LineNumberTextBox.Font = richTextBox1.Font;
4. richTextBox1.Select();
5. AddLineNumbers();
6. }
Resize
1. private void Form1_Resize(object sender, EventArgs e)
2. {
3. AddLineNumbers();
4. }

Step 6: Add following events & code to richTextBox1.

SelectionChanged
1. private void richTextBox1_SelectionChanged(object sender, EventArgs e)
2. {
3. Point pt = richTextBox1.GetPositionFromCharIndex(richTextBox1.SelectionStart);
4. if (pt.X == 1)
5. {
6. AddLineNumbers();
7. }
8. }
VScroll
1. private void richTextBox1_VScroll(object sender, EventArgs e)
2. {
3. LineNumberTextBox.Text = "";
4. AddLineNumbers();
5. LineNumberTextBox.Invalidate();
6. }
TextChanged
1. private void richTextBox1_TextChanged(object sender, EventArgs e)
2. {
3. if (richTextBox1.Text == "")
4. {
5. AddLineNumbers();
6. }
7. }
FontChanged
1. private void richTextBox1_FontChanged(object sender, EventArgs e)
2. {
3. LineNumberTextBox.Font = richTextBox1.Font;
4. richTextBox1.Select();
5. AddLineNumbers();
6. }

Step 7: Add following events & code to LineNumberTextBox.

MouseDown
1. private void LineNumberTextBox_MouseDown(object sender, MouseEventArgs e)
2. {
3. richTextBox1.Select();
4. LineNumberTextBox.DeselectAll();
5. }

Step 8: Debug your Form & check it out.

Complete Code

using System;
using System.Drawing;
using System.Windows.Forms;
namespace LineNumbers_CSharp
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
public int getWidth()
{
int w = 25;
// get total lines of richTextBox1
int line = richTextBox1.Lines.Length;
if (line <= 99)
{
w = 20 + (int)richTextBox1.Font.Size;
}
else if (line <= 999)
{
w = 30 + (int)richTextBox1.Font.Size;
}
else
{
w = 50 + (int)richTextBox1.Font.Size;
}
return w;
}
public void AddLineNumbers()
{
// create & set Point pt to (0,0)
Point pt = new Point(0, 0);
// get First Index & First Line from richTextBox1
int First_Index = richTextBox1.GetCharIndexFromPosition(pt);
int First_Line = richTextBox1.GetLineFromCharIndex(First_Index);
// set X & Y coordinates of Point pt to ClientRectangle Width & Height respectively
pt.X = ClientRectangle.Width;
pt.Y = ClientRectangle.Height;
// get Last Index & Last Line from richTextBox1
int Last_Index = richTextBox1.GetCharIndexFromPosition(pt);
int Last_Line = richTextBox1.GetLineFromCharIndex(Last_Index);
// set Center alignment to LineNumberTextBox
LineNumberTextBox.SelectionAlignment = HorizontalAlignment.Center;
// set LineNumberTextBox text to null & width to getWidth() function value
LineNumberTextBox.Text = "";
LineNumberTextBox.Width = getWidth();
// now add each line number to LineNumberTextBox upto last line
for (int i = First_Line; i <= Last_Line + 2; i++)
{
LineNumberTextBox.Text += i + 1 + "\n";
}
}
private void Form1_Load(object sender, EventArgs e)
{
LineNumberTextBox.Font = richTextBox1.Font;
richTextBox1.Select();
AddLineNumbers();
}
private void richTextBox1_SelectionChanged(object sender, EventArgs e)
{
Point pt = richTextBox1.GetPositionFromCharIndex(richTextBox1.SelectionStart);
if (pt.X == 1)
{
AddLineNumbers();
}
}
private void richTextBox1_VScroll(object sender, EventArgs e)
{
LineNumberTextBox.Text = "";
AddLineNumbers();
LineNumberTextBox.Invalidate();
}
private void richTextBox1_TextChanged(object sender, EventArgs e)
{
if (richTextBox1.Text == "")
{
AddLineNumbers();
}
}
private void richTextBox1_FontChanged(object sender, EventArgs e)
{
LineNumberTextBox.Font = richTextBox1.Font;
richTextBox1.Select();
AddLineNumbers();
}
private void LineNumberTextBox_MouseDown(object sender, MouseEventArgs e)
{
richTextBox1.Select();
LineNumberTextBox.DeselectAll();
}
private void Form1_Resize(object sender, EventArgs e)
{
AddLineNumbers();
}
}
}