c＃richtextbox行号列

Question

所以我在C＃中有一个Windows窗体，只有2个富文本框。

我用作文本编辑器的主框和左边的另一个框作为行号列。一切都很好。我想知道如何使行号列富文本框，如果启用自动换行则不打印行号，如果按下回车键则再次开始打印行号。这应该类似于Notepad ++。

1 line 1
2 line 2
3 line 3
4 line 4 - This is a word wrap line that carries on and on. This is a 
  word wrap line that carries on and on. word wrap line that carries on
  and on. This is a word wrap line that carries on and on.
5 line 5
6 line 6

这是我正在使用的代码

  public Form1()
    {
        InitializeComponent();
    }

    public void AddLineNumbers()
    {
        richTextBox1.Select();
        Point pt = new Point(0, 0);
        int First_Index = richTextBox1.GetCharIndexFromPosition(pt);
        int First_Line = richTextBox1.GetLineFromCharIndex(First_Index);
        pt.X = ClientRectangle.Width;
        pt.Y = ClientRectangle.Height;
        int Last_Index = richTextBox1.GetCharIndexFromPosition(pt);
        int Last_Line = richTextBox1.GetLineFromCharIndex(Last_Index);
        richTextBox2.SelectionAlignment = HorizontalAlignment.Center;
        richTextBox2.Text = "";
        for (int i = First_Line; i <= Last_Line + 1; i++)
        {
            richTextBox2.Text += i + 1 + "\n";
        }
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        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)
    {
        AddLineNumbers();
    }