二进制文件需要通过FileStream实例化的对象来实例化二进制写入流对象，在读取的时候则需要转换为二进制的内容

设计界面.PNG

代码

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

namespace WindowsFormsApp14
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void btnSave_Click(object sender, EventArgs e)
        {
            if (textBox1.Text == "")
            {
                MessageBox.Show("请输入写入内容！");
            }
            else
            {
                saveFileDialog1.Filter = "二进制文件(*.bmp)|*.bmp";
                //设置文件保存格式
                if (saveFileDialog1.ShowDialog() == DialogResult.OK)
                {
                    ////如果保存对话框打开了
                    FileStream f = new FileStream(saveFileDialog1.FileName, FileMode.OpenOrCreate,
                        FileAccess.ReadWrite);
                    //实例化FileStream对象，saveFileDialog1.FileName为用户输入的文件名
                    BinaryWriter w = new BinaryWriter(f);
                    //实例化BinaryWriter对象
                    w.Write(textBox1.Text);
                    //写入内容
                    w.Close();//关闭二进制写入流
                    f.Close();//关闭文件流
                    textBox1.Clear();
                }
            }
        }

        private void btnRead_Click(object sender, EventArgs e)
        {
            openFileDialog1.Filter = "二进制文件(*.bmp)|*.bmp";
            //设置文件读取格式
            if (openFileDialog1.ShowDialog() == DialogResult.OK)
            {
                ////如果保存对话框打开了
                FileStream f = new FileStream(saveFileDialog1.FileName, FileMode.Open,
                    FileAccess.Read);
                //实例化FileStream对象，saveFileDialog1.FileName为用户输入的文件名
                BinaryReader r = new BinaryReader(f);
                //实例化BinaryReader对象
                if (r.BaseStream.Position < r.BaseStream.Length)
                {
                    //判断不超出流的结尾
                    textBox1.Text = Convert.ToString(r.ReadUInt32());
                }
                r.Close();//关闭二进制读取流
                f.Close();//关闭文件流

            }
        }
    }
}