练习：WinForm 对话框控件（文件读取、写入）

设计界面：

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

namespace 对话框
{
    public partial class Form2 : Form
    {
        public Form2()
        {
            InitializeComponent();
        }

        #region 读取数据
        private void button2_Click(object sender, EventArgs e)
        {
            //显示工具
            DialogResult dr = openFileDialog1.ShowDialog();

            //取值
            if (dr == DialogResult.OK)
            {
                //文件路径
                string path = openFileDialog1.FileName;

                //文件流
                FileStream fs = new FileStream(path,FileMode.Open,FileAccess.Read);

                //读取
                byte[] sj=new byte[fs.Length]; //造一个二进制数组，用来存储读到的数据
                
                fs.Read(sj,0,sj.Length); //将文件读取为二进制数据，并且放到二进制数组里边

                //将二进制数据转为字符串
                richTextBox1.Text = Encoding.Default.GetString(sj);

                //关闭流
                fs.Close();
            }
        }
        #endregion

        #region 写入数据
        private void button1_Click(object sender, EventArgs e)
        {
            //显示选择文件对话框
            DialogResult dr=saveFileDialog1.ShowDialog();
            
            //获取路径
            if (dr == DialogResult.OK)
            {
                string path = saveFileDialog1.FileName;   //文件路径
                string nr = richTextBox1.Text; //取出文本框中的内容
                byte[] sj = Encoding.Default.GetBytes(nr);  //将字符串转为二进制数组

                //造文件流
                FileStream fs = new FileStream(path,FileMode.Create);

                //向文件里边写数据
                fs.Write(sj,0,sj.Length);

                //关闭流
                fs.Close();
            }
        }
        #endregion
    }
}