richTextBoxFontClass

使用

private void button1_Click(object sender, EventArgs e)
{
    RichTextBoxCtrl.richTextBoxFontClass r = new RichTextBoxCtrl.richTextBoxFontClass();
    r.richTextBox = richTextBox1;
    r.ToggleBold();
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Drawing;

////使用
//RichTextBoxCtrl.richTextBoxFontClass r = new RichTextBoxCtrl.richTextBoxFontClass();
//r.richTextBox = richTextBox1;
//r.ToggleBold();

namespace RichTextBoxCtrl
{
    class richTextBoxFontClass
    {

        public richTextBoxFontClass()
        {
            richTextBox = new RichTextBox();
        }
        public RichTextBox richTextBox;

        //粗体
        public void ToggleBold()
        {
            if (richTextBox.SelectionFont == null)
                richTextBox.SelectionFont = richTextBox.Font;

            FontStyle style = richTextBox.SelectionFont.Style;

            if (richTextBox.SelectionFont.Bold)

                style &= ~FontStyle.Bold;//恢复正常
            else
                style |= FontStyle.Bold;

            richTextBox.SelectionFont = new Font(richTextBox.SelectionFont, style);
        }

        //斜体
        public void ToggleItalic()
        {
            if (richTextBox.SelectionFont == null)
                richTextBox.SelectionFont = richTextBox.Font;

            FontStyle style = richTextBox.SelectionFont.Style;

            if (richTextBox.SelectionFont.Italic)
                style &= ~FontStyle.Italic;//恢复正常
            else
                style |= FontStyle.Italic;

            richTextBox.SelectionFont = new Font(richTextBox.SelectionFont, style);
        }

        //下划线
        public void ToggleUnderLine()
        {
            if (richTextBox.SelectionFont == null)
                richTextBox.SelectionFont = richTextBox.Font;

            FontStyle style = richTextBox.SelectionFont.Style;

            if (richTextBox.SelectionFont.Underline)
                style &= ~FontStyle.Underline;//恢复正常
            else
                style |= FontStyle.Underline;

            richTextBox.SelectionFont = new Font(richTextBox.SelectionFont, style);
        }

        //删除线
        public void ToggleStrikeout()
        {
            if (richTextBox.SelectionFont == null)
                richTextBox.SelectionFont = richTextBox.Font;

            FontStyle style = richTextBox.SelectionFont.Style;

            if (richTextBox.SelectionFont.Strikeout)
                style &= ~FontStyle.Strikeout;//恢复正常
            else
                style |= FontStyle.Strikeout;
            richTextBox.SelectionFont = new Font(richTextBox.SelectionFont, style);
        }
    }
}