一个简单的文件MD5码自动计算比较器（附源码）

主要对 多线程更新 winform 不是特别清楚，绕来绕去，搞得很晕乎，主要代码如下， 还请各位大侠多多指点，谢谢！

代码如下:
using System;
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Data;
 using System.Drawing;
 using System.Linq;
 using System.Text;
 using System.Windows.Forms;
 using System.Security.Cryptography;
 using System.IO;
 using System.Threading;

 namespace FileMD5 {
     public partial class MainForm : Form {
         public MainForm() {
             InitializeComponent();
         }

         private void button_file_Click(object sender, EventArgs e) {
             OpenFileDialog fileDialog = new OpenFileDialog();
             fileDialog.Title = "请选择文件";
             fileDialog.RestoreDirectory = true;

             if (fileDialog.ShowDialog() == DialogResult.OK) {
                 textBox_file.Text = fileDialog.FileName;
                 textBox_result.Text = "";
                 FileInfo file = new FileInfo(fileDialog.FileName);
                 fileSzie = file.Length;
                 showFilesize(fileSzie);
             }

         }

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

         private void button_check_Click(object sender, EventArgs e) {
             checkResult();
         }

         MD5 md5 = (MD5)CryptoConfig.CreateFromName("MD5");
         long fileSzie = 0;

         private void button_calc_Click(object sender, EventArgs e) {