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;
            }
        }
    }
}