C# winform实现下载带进度条

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 MetroFramework.Forms;
 
 namespace KMS_Starter
 {
     public partial class Form2 : MetroForm
     {
         public Form2()
         {
             InitializeComponent();
         }
 
         private void Form2_Load(object sender, EventArgs e)
         {
 
         }
 
         private void metroButton1_Click(object sender, EventArgs e)
         {
             DownloadFile("http://localhost:1928/WebServer/downloader/123.rar", @"C:123.rar", metroProgressBar1, label2);
         }
         /// <summary>        
         /// c#,.net 下载文件        
         /// </summary>        
         /// <param name="URL">下载文件地址</param>       
         /// 
         /// <param name="Filename">下载后的存放地址</param>        
         /// <param name="Prog">用于显示的进度条</param>        
         /// 
         public void DownloadFile(string URL, string filename, System.Windows.Forms.ProgressBar prog, System.Windows.Forms.Label label1)
         {
             float percent = 0;
             try
             {
                 System.Net.HttpWebRequest Myrq = (System.Net.HttpWebRequest)System.Net.HttpWebRequest.Create(URL);
                 System.Net.HttpWebResponse myrp = (System.Net.HttpWebResponse)Myrq.GetResponse();
                 long totalBytes = myrp.ContentLength;
                 if (prog != null)
                 {
                     prog.Maximum = (int)totalBytes;
                 }
                 System.IO.Stream st = myrp.GetResponseStream();
                 System.IO.Stream so = new System.IO.FileStream(filename, System.IO.FileMode.Create);
                 long totalDownloadedByte = 0;
                 byte[] by = new byte[1024];
                 int osize = st.Read(by, 0, (int)by.Length);
                 while (osize > 0)
                 {
                     totalDownloadedByte = osize + totalDownloadedByte;
                     System.Windows.Forms.Application.DoEvents();
                     so.Write(by, 0, osize);
                     if (prog != null)
                     {
                         prog.Value = (int)totalDownloadedByte;
                     }
                     osize = st.Read(by, 0, (int)by.Length);
 
                     percent = (float)totalDownloadedByte / (float)totalBytes * 100;
                     label2.Text = "当前补丁下载进度" + percent.ToString() + "%";
                     System.Windows.Forms.Application.DoEvents(); //必须加注这句代码，否则label1将因为循环执行太快而来不及显示信息
                 }
                 so.Close();
                 st.Close();
             }
             catch (System.Exception)
             {
                 throw;
             }
         }
     }
 }