[C#]richtextbox實作行号

editorControl是一個userControl，其包含兩個控件：左側是一個用來顯示行号的RichTextBox（使用label等均可），右側是一個繼承自RichTextBox的componenteditorGrid1。

/*實作行号 begin*/

(1) 添加事件
        private void richTextBoxMain_TextChanged(object sender, EventArgs e)
        {
            updateLabelRowIndex();
        }

        private void richTextBoxMain_FontChanged(object sender, EventArgs e)
        {
            updateLabelRowIndex();
            richTextBoxMain_VScroll(null, null);
        }

        private void richTextBoxMain_Resize(object sender, EventArgs e)
        {
            richTextBoxMain_VScroll(null, null);
        }

        private void richTextBoxMain_VScroll(object sender, EventArgs e)
        {
            //move location of numberLabel for amount of pixels caused by scrollbar
            int p = richTextBoxMain.GetPositionFromCharIndex(0).Y % (richTextBoxMain.Font.Height + 1);
            labelRowIndex.Location = new Point(0,p);
            updateLabelRowIndex();
        }

(2)更新行号的函數

        private void updateLabelRowIndex()
        {
            //we get index of first visible char and number of first visible line
            Point pos = new Point(0,0);
            int firstIndex = this.richTextBoxMain.GetCharIndexFromPosition(pos);
            int firstLine = this.richTextBoxMain.GetLineFromCharIndex(firstIndex);

            //now we get index of last visible char and number of last visible line
            pos.X += this.richTextBoxMain.ClientRectangle.Width;
            pos.Y += this.richTextBoxMain.ClientRectangle.Height;
            int lastIndex = this.richTextBoxMain.GetCharIndexFromPosition(pos);
            int lastLine = this.richTextBoxMain.GetLineFromCharIndex(lastIndex);

            //this is point position of last visible char, 
            //we'll use its Y value for calculating numberLabel size
            pos = this.richTextBoxMain.GetPositionFromCharIndex(lastIndex);

            labelRowIndex.Text = "";
            for (int i = firstLine; i <= lastLine +1 ; i++)
            {
                labelRowIndex.Text += i + 1 + "\r\n";
            }
        }     
        /*end*/