如何限制DownloadString(url)允许的时间为500毫秒？

我正在编写一个程序，当 textBox1 更改时：

URL = "http://example.com/something/";
URL += System.Web.HttpUtility.UrlEncode(textBox1.Text);
s = new System.Net.WebClient().DownloadString(URL);

我想将 DownloadString(URL) 允许的时间限制为 500 毫秒。如果超过，则取消。

没有这样的属性，但您可以轻松扩展WebClient:

public class TimedWebClient: WebClient
{
    // Timeout in milliseconds, default = 600,000 msec
    public int Timeout { get; set; }

    public TimedWebClient()
    {
        this.Timeout = 600000; 
    }

    protected override WebRequest GetWebRequest(Uri address)
    {
        var objWebRequest= base.GetWebRequest(address);
        objWebRequest.Timeout = this.Timeout;
        return objWebRequest;
    }
}

// use
string s = new TimedWebClient {Timeout = 500}.DownloadString(URL);