WebClient多文件下载错误

本文关键字：错误 文件下载 WebClient | 更新日期: 2023-09-27 18:10:39

我使用以下代码从我的web服务器下载50多个文件

private void button5_Click(object sender, EventArgs e)
{
WebClient client = new WebClient();
client.DownloadProgressChanged += new DownloadProgressChangedEventHandler(client_DownloadProgressChanged);
client.DownloadFileCompleted += new AsyncCompletedEventHandler(client_DownloadFileCompleted);
//downloads
client.DownloadFileAsync(new Uri("http://www.site.com/file/loc.file"), @"c:'app'loc ");
client.DownloadFileAsync(new Uri("http://www.site.com/file/loc.file"), @"c:'app'loc ");
client.DownloadFileAsync(new Uri("http://www.site.com/file/loc.file"), @"c:'app'loc ");
 }
           void client_DownloadProgressChanged(object sender, DownloadProgressChangedEventArgs e)
    {
        double bytesIn = double.Parse(e.BytesReceived.ToString());
        double totalBytes = double.Parse(e.TotalBytesToReceive.ToString());
        double percentage = bytesIn / totalBytes * 100;
        progressBar.Value = int.Parse(Math.Truncate(percentage).ToString());
    }
    private void client_DownloadFileCompleted(object sender, AsyncCompletedEventArgs e)
    {
        MessageBox.Show("Game Update Finished!");
    }

我想下载一个文件在一个持续的进度条，我得到了大部分的编码完成，但当我点击"下载"按钮，我得到以下错误

WebClient不支持并发I/O操作

我需要做什么?

WebClient多文件下载错误

感受不同:

  • 它可以以并行方式下载多个文件(每一个流)一个文件)。
  • 但是不能使用多个流下载一个文件。

下面是一个例子(主窗口包含一个"开始"按钮和五个进度条):

public partial class MainWindow : Window
{
    private WebClient _webClient;
    private ProgressBar[] _progressBars;
    private int _index = 0;
    public MainWindow()
    {
        InitializeComponent();
        _progressBars = new [] {progressBar1, progressBar2, progressBar3, progressBar4, progressBar5};
        ServicePointManager.DefaultConnectionLimit = 5;
    }
    private void button1_Click(object sender, RoutedEventArgs e)
    {
        Interlocked.Increment(ref _index);
        if (_index > _progressBars.Length)
            return;
        _webClient = new WebClient();
        _webClient.DownloadProgressChanged += WebClient_DownloadProgressChanged;
        _webClient.DownloadFileCompleted += WebClient_DownloadFileCompleted;
        _webClient.DownloadFileAsync(new Uri("http://download.thinkbroadband.com/5MB.zip"),
                                     System.IO.Path.GetTempFileName(),
                                     _index);
    }
    private void WebClient_DownloadProgressChanged(object sender, DownloadProgressChangedEventArgs args)
    {
        var index = (int) args.UserState;
        _progressBars[index-1].Value = args.ProgressPercentage;
    }
    private void WebClient_DownloadFileCompleted(object sender, AsyncCompletedEventArgs args)
    {
        var index = (int)args.UserState;
        MessageBox.Show(args.Error == null
                            ? string.Format("Download #{0} completed!", index)
                            : string.Format("Download #{0} error!'n'n{1}", index, args.Error));
    }
}

您正在使用同一个WebClient实例并行运行多个下载-错误告诉您这是不支持的-您要么:

  • 使用多个WebClient实例(每次并行下载一个)或
  • 一个接一个下载

相关信息:

  • http://msdn.microsoft.com/en-us/library/system.net.webclient.aspx
  • http://msdn.microsoft.com/en-us/magazine/cc700359.aspx

WebClient不支持每个实例并发I/O操作(多个下载)，因此您需要为每个下载创建一个单独的WebClient实例。您仍然可以异步执行每个下载，并使用相同的事件处理程序。

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