C#中关于打开文本更改其中字体并保存的代码

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Windows;
using System.IO;

namespace exer_2
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}

private void button4_Click(object sender, EventArgs e)
{
this.Close();
}

private void button2_Click(object sender, EventArgs e)
{
if (openFileDialog1.ShowDialog() == System.Windows.Forms.DialogResult.OK)
richTextBox1.LoadFile(openFileDialog1.FileName, System.Windows.Forms.
RichTextBoxStreamType.PlainText);

}

private void button3_Click(object sender, EventArgs e)
{

SaveFileDialog saveFile1 = new SaveFileDialog();
saveFile1.DefaultExt = "*.rtf"; ;
saveFile1.Filter = "RTF Files|*.rtf";
if (saveFile1.ShowDialog() == System.Windows.Forms.DialogResult.OK &&
saveFile1.FileName.Length > 0)
{

richTextBox1.SaveFile(saveFile1.FileName, RichTextBoxStreamType.RichNoOleObjs);
}

MessageBox.Show("已保存", "提示：");

}

private void button1_Click(object sender, EventArgs e)
{

fontDialog1.ShowColor = true;

fontDialog1.Font = richTextBox1.SelectionFont;
fontDialog1.Color = richTextBox1.SelectionColor;

if (fontDialog1.ShowDialog() != DialogResult.Cancel)
{
richTextBox1.SelectionFont = fontDialog1.Font;
richTextBox1.SelectionColor = fontDialog1.Color;
}

}

private void richTextBox1_MouseDown(object sender, MouseEventArgs e)
{

this.richTextBox1.TabIndex = 0;
this.richTextBox1.SelectionStart = 0;
this.richTextBox1.SelectionColor = Color.Red;

}

private void richTextBox1_MouseUp(object sender, MouseEventArgs e)
{
this.richTextBox1.SelectionColor = Color.Red;
this.richTextBox1.Show();

}

}
}