C# 使用Parallel去执行并行下载

直接上代码：

	//最大线程下载数量ParallelOptions options = new ParallelOptions{MaxDegreeOfParallelism = 5};public async Task DownloadMusicUrl(List<MusicTags> musicTags){DateTime currentTime = DateTime.Now;DateTime startTime = new DateTime(1970, 1, 1);TimeSpan timeSpan = currentTime - startTime;string timestamp = ((long)timeSpan.TotalMilliseconds).ToString();string type = string.Empty;if (this.mp3.Checked) type = this.mp3.Text;if (this.flac.Checked) type = this.flac.Text;if (this.mv.Checked) type = this.mv.Text; 并行下载URL列表中的所有文件List<Task> downloadTasks = new List<Task>();Parallel.ForEach(musicTags, options, tag =>{Task task = Download(tag, timestamp, type);downloadTasks.Add(task); // 将下载任务的 Task 添加到 downloadTasks 列表中await Task.Delay(500);});await Task.WhenAll(downloadTasks C#有偿Q群：927860652); // 等待所有下载任务完成}

这里切记先用 Task task = Download(tag, timestamp, type);把任务添加到集合，不要直接await在ForEach的委托里面执行代码，这样会出现一些无法控制的bug，任务添加完成后，在最外面await Task.WhenAll(downloadTasks); 通过这个等待下载完成。
这样就可以很好的控制并行下载呢。

       public async Task Download(MusicTags tag, string timestamp, string type = "mp3"){using (WebClient webClient = new WebClient()){try{string solutionPath = Path.GetDirectoryName(Path.GetDirectoryName(Path.GetDirectoryName(Path.GetDirectoryName(AppDomain.CurrentDomain.BaseDirectory))));string folderPath = Path.Combine(solutionPath, "资源下载", DateTime.Now.ToString("yyyyMMdd"), timestamp);gloFolderPath = folderPath;Directory.CreateDirectory(folderPath);string name = $"{tag.baseMusic.SongTitle}-{tag.baseMusic.Singer}.{type}";// 设置下载完成后保存的本地路径和文件名string localPath = Path.Combine(folderPath, name); // 替换为保存路径// 订阅 DownloadProgressChanged 事件来更新进度条webClient.DownloadProgressChanged += (s, args) =>{int progress = args.ProgressPercentage;long bytesReceived = args.BytesReceived;long totalBytesToReceive = args.TotalBytesToReceive;UpdateProgressBar(progress, bytesReceived, totalBytesToReceive, name);};await webClient.DownloadFileTaskAsync(new Uri(tag.tag), localPath);//Console.WriteLine("音乐下载完成，保存路径：" + localPath);}catch (Exception ex){Console.WriteLine("音乐下载失败：" + ex.Message + ex.StackTrace);}}// 下载完成后，更新进度条为 100%UpdateProgressBar(100, 0, 0, "下载完成");AppendLog($"{tag.baseMusic.SongTitle}-{tag.baseMusic.Singer} 已下载");}