Why is this hanging?

Question

private async void button1_Click(object sender, EventArgs e)
    {
        var cookie = webBrowser1.Document.Cookie;
        await
            Task.WhenAll(
                listBox1
                .Items
                .Cast<string>()
                .Select(async s =>
                {
                    var data = "action=relationship&user_id=" + s + "&relation=follow";
                    var req = WebRequest.Create("http://example.com") as HttpWebRequest;
                    req.Method = "POST";
                    req.ContentType = "application/x-www-form-urlencoded";
                    req.ContentLength = data.Length;
                    req.Headers["cookie"] = cookie;
                    using (var sw = new StreamWriter(await req.GetRequestStreamAsync(), Encoding.ASCII))
                    {
                        sw.Write(data);
                        sw.Close();
                    }
                }));
        listBox1.Items.Clear();
    }

I've tried this a million times, and it runs it two times every time. And when it runs it those two times, it does what it's supposed to.

What it's supposed to do is take items from a listbox, and use each item as part of a POST request. Then when it's done, it clears the listbox.

Can someone explain what's wrong?

Answer 1

You should call req.GetResponseAsync() to actually send the request.