C#限速下载网络文件的方法，具体如下：

using System;using System.Collections.Concurrent;using System.Collections.Generic;using System.ComponentModel;using System.Data;using System.Drawing;using System.IO;using System.Linq;using System.Net;using System.Text;using System.Text.RegularExpressions;using System.Threading;using System.Threading.Tasks;using System.Windows.Forms;using Common.Utils;using Utils;namespace 爬虫{ public partial class Form1 : Form { #region 变量 /// <summary> /// 已完成字节数 /// </summary> private long completedCount = 0; /// <summary> /// 是否完成 /// </summary> private bool isCompleted = true; /// <summary> /// 数据块队列 /// </summary> private ConcurrentQueue<MemoryStream> msQueue = new ConcurrentQueue<MemoryStream>(); /// <summary> /// 下载开始位置 /// </summary> private long range = 0; /// <summary> /// 文件大小 /// </summary> private long total = 0; /// <summary> /// 一段时间内的完成节点数，计算网速用 /// </summary> private long unitCount = 0; /// <summary> /// 上次计时时间，计算网速用 /// </summary> private DateTime lastTime = DateTime.MinValue; /// <summary> /// 一段时间内的完成字节数，控制网速用 /// </summary> private long unitCountForLimit = 0; /// <summary> /// 上次计时时间，控制网速用 /// </summary> private DateTime lastTimeForLimit = DateTime.MinValue; /// <summary> /// 下载文件sleep时间，控制速度用 /// </summary> private int sleepTime = 1; #endregion #region Form1 public Form1() { InitializeComponent(); } #endregion #region Form1_Load private void Form1_Load(object sender, EventArgs e) { lblMsg.Text = string.Empty; lblByteMsg.Text = string.Empty; lblSpeed.Text = string.Empty; } #endregion #region Form1_FormClosing private void Form1_FormClosing(object sender, FormClosingEventArgs e) { } #endregion #region btnDownload_Click 下载 private void btnDownload_Click(object sender, EventArgs e) { isCompleted = false; btnDownload.Enabled = false; string url = txtUrl.Text.Trim(); string filePath = CreateFilePath(url); #region 下载线程 Thread thread = new Thread(new ThreadStart(() => { int tryTimes = 0; while (!HttpDownloadFile(url, filePath)) { Thread.Sleep(10000); tryTimes++; LogUtil.Log("请求服务器失败，重新请求" + tryTimes.ToString() + "次"); this.Invoke(new InvokeDelegate(() => { lblMsg.Text = "请求服务器失败，重新请求" + tryTimes.ToString() + "次"; })); HttpDownloadFile(url, filePath); } })); thread.IsBackground = true; thread.Start(); #endregion #region 保存文件线程 thread = new Thread(new ThreadStart(() => { while (!isCompleted) { MemoryStream ms; if (msQueue.TryDequeue(out ms)) { using (FileStream fs = new FileStream(filePath, FileMode.Open, FileAccess.Write)) { fs.Seek(completedCount, SeekOrigin.Begin); fs.Write(ms.ToArray(), 0, (int)ms.Length); fs.Close(); } completedCount += ms.Length; } if (total != 0 && total == completedCount) { Thread.Sleep(100); isCompleted = true; } Thread.Sleep(1); } })); thread.IsBackground = true; thread.Start(); #endregion #region 计算网速/进度线程 thread = new Thread(new ThreadStart(() => { while (!isCompleted) { Thread.Sleep(1000); if (lastTime != DateTime.MinValue) { double sec = DateTime.Now.Subtract(lastTime).TotalSeconds; double speed = unitCount / sec / 1024; try { #region 显示速度 if (speed < 1024) { this.Invoke(new InvokeDelegate(() => { lblSpeed.Text = string.Format("{0}KB/S", speed.ToString("0.00")); })); } else { this.Invoke(new InvokeDelegate(() => { lblSpeed.Text = string.Format("{0}MB/S", (speed / 1024).ToString("0.00")); })); } #endregion #region 显示进度 this.Invoke(new InvokeDelegate(() => { string strTotal = (total / 1024 / 1024).ToString("0.00") + "MB"; if (total < 1024 * 1024) { strTotal = (total / 1024).ToString("0.00") + "KB"; } string completed = (completedCount / 1024 / 1024).ToString("0.00") + "MB"; if (completedCount < 1024 * 1024) { completed = (completedCount / 1024).ToString("0.00") + "KB"; } lblMsg.Text = string.Format("进度：{0}/{1}", completed, strTotal); lblByteMsg.Text = string.Format("已下载：{0}\r\n总大小：{1}", completedCount, total); if (completedCount == total) { MessageBox.Show("完成"); } })); #endregion } catch { } lastTime = DateTime.Now; unitCount = 0; } } })); thread.IsBackground = true; thread.Start(); #endregion #region 限制网速线程 thread = new Thread(new ThreadStart(() => { while (!isCompleted) { Thread.Sleep(100); if (lastTimeForLimit != DateTime.MinValue) { double sec = DateTime.Now.Subtract(lastTimeForLimit).TotalSeconds; double speed = unitCountForLimit / sec / 1024; try { #region 限速/解除限速 double limitSpeed = 0; if (double.TryParse(txtSpeed.Text.Trim(), out limitSpeed)) { if (speed > limitSpeed && sleepTime < 1000) { sleepTime += 1; } if (speed < limitSpeed - 10 && sleepTime >= 2) { sleepTime -= 1; } } else { this.Invoke(new InvokeDelegate(() => { txtSpeed.Text = "100"; })); } #endregion } catch { } lastTimeForLimit = DateTime.Now; unitCountForLimit = 0; } } })); thread.IsBackground = true; thread.Start(); #endregion } #endregion #region HttpDownloadFile 下载文件 /// <summary> /// Http下载文件 /// </summary> public bool HttpDownloadFile(string url, string filePath) { try { if (!File.Exists(filePath)) { using (FileStream fs = new FileStream(filePath, FileMode.Create)) { fs.Close(); } } else { FileInfo fileInfo = new FileInfo(filePath); range = fileInfo.Length; } // 设置参数 HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest; request.UserAgent = "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0; Trident/4.0)"; request.Proxy = null; //发送请求并获取相应回应数据 HttpWebResponse response = request.GetResponse() as HttpWebResponse; if (response.ContentLength == range) { this.Invoke(new InvokeDelegate(() => { lblMsg.Text = "文件已下载"; })); return true; } // 设置参数 request = WebRequest.Create(url) as HttpWebRequest; request.UserAgent = "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0; Trident/4.0)"; request.Proxy = null; request.AddRange(range); //发送请求并获取相应回应数据 response = request.GetResponse() as HttpWebResponse; //直到request.GetResponse()程序才开始向目标网页发送Post请求 Stream responseStream = response.GetResponseStream(); total = range + response.ContentLength; completedCount = range; MemoryStream ms = new MemoryStream(); byte[] bArr = new byte[1024]; lastTime = DateTime.Now; lastTimeForLimit = DateTime.Now; int size = responseStream.Read(bArr, 0, (int)bArr.Length); unitCount += size; unitCountForLimit += size; ms.Write(bArr, 0, size); while (!isCompleted) { size = responseStream.Read(bArr, 0, (int)bArr.Length); unitCount += size; unitCountForLimit += size; ms.Write(bArr, 0, size); if (ms.Length > 102400) { msQueue.Enqueue(ms); ms = new MemoryStream(); } if (completedCount + ms.Length == total) { msQueue.Enqueue(ms); ms = new MemoryStream(); } Thread.Sleep(sleepTime); } responseStream.Close(); return true; } catch (Exception ex) { LogUtil.LogError(ex.Message + "\r\n" + ex.StackTrace); return false; } } #endregion #region 根据URL生成文件保存路径 private string CreateFilePath(string url) { string path = Application.StartupPath + "\\download"; if (!Directory.Exists(path)) { Directory.CreateDirectory(path); } string fileName = Path.GetFileName(url); if (fileName.IndexOf("?") > 0) { return path + "\\" + fileName.Substring(0, fileName.IndexOf("?")); } else { return path + "\\" + fileName; } } #endregion } //end Form1类}

测试截图：

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