如何在.net上为WebClient设置TimeOut？

我下载了一些文件，但我也想为webclient设置超时 . 我看到没有变化只是我们可以使用重写WebRequest . 我已经做了但它不起作用 . 我的意思是重写GetWebRequest方法不起作用..这是我的代码

public class VideoDownloader : Downloader
{
    /// <summary>
    /// Initializes a new instance of the <see cref="VideoDownloader"/> class.
    /// </summary>
    /// <param name="video">The video to download.</param>
    /// <param name="savePath">The path to save the video.</param>
    public VideoDownloader(VideoInfo video, string savePath)
        : base(video, savePath)
    { }


    /// <summary>
    /// Starts the video download.
    /// </summary>
    public override void Execute()
    {
        // We need a handle to keep the method synchronously
        var handle = new ManualResetEvent(false);

        var client = new WebClient();


        client.DownloadFileCompleted += (sender, args) => handle.Set();
        client.DownloadProgressChanged += (sender, args) =>
        this.OnProgressChanged(new ProgressEventArgs(args.ProgressPercentage));

        this.OnDownloadStarted(EventArgs.Empty);

      client.DownloadFileAsync(new Uri(this.Video.DownloadUrl), this.SavePath);

        handle.WaitOne();
        handle.Close();


        this.OnDownloadFinished(EventArgs.Empty);
    }

    protected override WebRequest GetWebRequest(Uri address)
    {
        WebRequest w = base.GetWebRequest(address);
        w.Timeout = 10*1000; // 20 * 60 * 1000;
        return w;

    }

}

And the Download class

public abstract class Downloader: WebClient
{
    /// <summary>
    /// Initializes a new instance of the <see cref="Downloader"/> class.
    /// </summary>
    /// <param name="video">The video to download/convert.</param>
    /// <param name="savePath">The path to save the video/audio.</param>
    protected Downloader(VideoInfo video, string savePath)
    {
        this.Video = video;
        this.SavePath = savePath;
    }

    protected override WebRequest GetWebRequest(Uri address)
    {
        WebRequest w = base.GetWebRequest(address);
        w.Timeout = 10 * 1000; // 20 * 60 * 1000;
        return w;

    }

    /// <summary>
    /// Occurs when the download finished.
    /// </summary>
    public event EventHandler DownloadFinished;

    /// <summary>
    /// Occurs when the download is starts.
    /// </summary>
    public event EventHandler DownloadStarted;

    /// <summary>
    /// Occurs when the progress has changed.
    /// </summary>
    public event EventHandler<ProgressEventArgs> ProgressChanged;

    /// <summary>
    /// Gets the path to save the video/audio.
    /// </summary>
    public string SavePath { get; private set; }

    /// <summary>
    /// Gets the video to download/convert.
    /// </summary>
    public VideoInfo Video { get; private set; }

    /// <summary>
    /// Starts the work of the <see cref="Downloader"/>.
    /// </summary>
    public abstract void Execute();

    protected void OnDownloadFinished(EventArgs e)
    {
        if (this.DownloadFinished != null)
        {
            this.DownloadFinished(this, e);
        }

    }

    protected void OnDownloadStarted(EventArgs e)
    {
        if (this.DownloadStarted != null)
        {
            this.DownloadStarted(this, e);
        }
    }

    protected void OnProgressChanged(ProgressEventArgs e)
    {
        if (this.ProgressChanged != null)
        {
            this.ProgressChanged(this, e);
        }
    }
}

我的错误在哪里？注意：我想下载异步