C# 使用webclient时，如何在OpenReadCompletedEvent中获取URL

当我使用webclient时，如何在OpenReadCompletedEvent中获取URL

 WebClient webClient = new WebClient();
 webClient.OpenReadAsync(url);       // in event method I want get this url       
 webClient.OpenReadCompleted += new OpenReadCompletedEventHandler(CardInfoDown_Completed);   


 private void CardInfoDown_Completed(object sender, OpenReadCompletedEventArgs e)
    {
        if (e.Error == null)
        {           
            using (System.IO.StreamReader reader = new System.IO.StreamReader(e.Result))
            {
                // I want get the url here,
                // How to do this?
                string strStream = reader.ReadToEnd();              
            }
        }          
    }

谢谢大家!

    WebClient webClient = new WebClient();
    webClient.BaseAddress = "http://hhh.com";
    webClient.OpenReadAsync(new Uri("http://hhh.com"));       // in event method I want get this url       
    webClient.OpenReadCompleted += new OpenReadCompletedEventHandler(CardInfoDown_Completed);

以及：

---

Anton Sizikov的解决方案很好，但只有在URL是绝对的（比如

http://hhh.com

）。如果使用相对URL，.NET将自动将基址与相对URL合并（因此可能导致无效URL）

要将值发送到

OpenReadCompleted

事件处理程序，您应该使用此

OpenRead

重载来提供自定义令牌（在本例中为您的URL）：

然后检索该值：

private void CardInfoDown_Completed(object sender, OpenReadCompletedEventArgs e)
{
    if (e.Error == null)
    {
        using (System.IO.StreamReader reader = new System.IO.StreamReader(e.Result))
        {
            var url = (string)e.UserState;
            string strStream = reader.ReadToEnd();
        }
    }
}

---

对我来说，即使是一个简单的变化，从上述工程罚款

    private void CardInfoDown_Completed(object sender, DownloadStringCompletedEventArgs e)
    {
        string url;

        if (e.Error == null)
        {
            url  = (string)e.UserState;
        }
       // ...
    }

---

为什么不将url保持为全局？并在活动中访问它？是的，我忘记了UserState，谢谢！在已完成的事件中，我将baseaddress设置为null。。你能猜出原因吗？嗯，我使用了DownloadStringCompletedEventArgs，但实际上它的成分可能与前面的示例相同。。

private void CardInfoDown_Completed(object sender, OpenReadCompletedEventArgs e)
{
    if (e.Error == null)
    {
        using (System.IO.StreamReader reader = new System.IO.StreamReader(e.Result))
        {
            var url = (string)e.UserState;
            string strStream = reader.ReadToEnd();
        }
    }
}

    private void CardInfoDown_Completed(object sender, DownloadStringCompletedEventArgs e)
    {
        string url;

        if (e.Error == null)
        {
            url  = (string)e.UserState;
        }
       // ...
    }