使用webclient时如何在OpenReadCompletedEvent中获取URL

Question

How can I get the URL in OpenReadCompletedEvent when I use webclient.

 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();              
            }
        }          
    }

Thank you!

Answer 1

    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);

And:

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?
            var client = sender as WebClient;
            if (client != null)
            {
                var url = client.BaseAddress; //returns hhh.com
            }
            string strStream = reader.ReadToEnd();
        }
    }

Answer 2

Anton Sizikov's solution is good, but will only work if the URL is absolute (like http://hhh.com ). If using a relative URL, .NET will automatically merge the base address with the relative URL (therefore potentially resulting in an invalid URL).

To send a value to the OpenReadCompleted event handler, you're supposed to use this OpenRead overload to provide a custom token (in this case, your URL): http://msdn.microsoft.com/en-us/library/ms144212(v=vs.95).aspx

WebClient webClient = new WebClient();
webClient.OpenReadAsync(new Uri("http://hhh.com"), "http://hhh.com");
webClient.OpenReadCompleted += new OpenReadCompletedEventHandler(CardInfoDown_Completed);

Then to retrieve the value:

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();
        }
    }
}

Answer 3

For me even a simpler variation from the above works fine

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

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