用c#写一个记事本,想把子窗体中的字体加粗,应该怎么办啊,请各位大虾多多指教.急啊

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private void buttonBold_Click(object sender, EventArgs e)
        {
            Font  oldFont;
            Font newFont;
            oldFont = this.richTextBoxText.SelectionFont;
            if (oldFont.Bold)
                //newFont = new Font(oldFont, oldFont.Style &  ~FontStyle.Bold);
                newFont = new Font(oldFont,oldFont.Style & ~FontStyle.Bold);
            else
                newFont = new Font(oldFont, oldFont.Style | FontStyle.Bold);
            this.richTextBoxText.SelectionFont = newFont;
           // this.richTextBoxText.Focus();
            this.richTextBoxText.Focus();
        }