Question

我使用以下代码从我的网络服务器下载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!");
    }

我希望一次下载1个文件并继续进度栏iv完成大部分编码但是当我点击“下载”按钮时出现以下错误

WebClient不支持并发I / O操作。

我需要做什么？

Answer 1

感受不同之处：

它可以并行方式下载多个文件（每个流一个流）一个文件）。
但它无法使用多个流下载一个文件。

以下是示例（MainWindow包含一个按钮'Start'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));
    }
}

Answer 2

您正在使用相同的WebClient实例并行运行多个下载 - 错误告诉您不支持此操作 - 您可以：

使用WebClient的多个实例（每个并行下载一个） OR
在另一个文件之后下载一个文件

WebClient多文件下载程序错误

3 个答案: