C＃Thread UI被阻止了| WebRequest.Create的可能原因？

Question

I'm currently having the issue, that something is blocking my UI thread . I know it is happening in the following function:

public async Task<string> function(string username, string password, string handle)
{
    try
    {
        string finalStr;

        HttpWebRequest request = (HttpWebRequest)WebRequest.Create("https://url.com");
        request.CookieContainer = cookie;
        request.AllowAutoRedirect = true;

        var response = await request.GetResponseAsync();

        string str = new StreamReader(response.GetResponseStream(), Encoding.UTF8).ReadToEnd();

        string str2 = this.getToken(str, "_token\" value=\"", "\">", 0);
        string[] textArray1 = new string[] { "postVariables=" + str2 };

        HttpWebRequest httpWebRequest_0 = (HttpWebRequest)WebRequest.Create("https://url.com");
        httpWebRequest_0.CookieContainer = cookie;
        httpWebRequest_0.Method = "POST";
        httpWebRequest_0.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8";
        httpWebRequest_0.Referer = "https://twitter.com/settings/account";
        httpWebRequest_0.UserAgent = "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/535.2 (KHTML, like Gecko) Chrome/15.0.874.121 Safari/535.2";
        httpWebRequest_0.AllowAutoRedirect = true;
        httpWebRequest_0.ContentType = "application/x-www-form-urlencoded";

        byte[] bytes = Encoding.ASCII.GetBytes(string.Concat(textArray1));
        httpWebRequest_0.ContentLength = bytes.Length;

        Stream requestStream = await httpWebRequest_0.GetRequestStreamAsync();
        await requestStream.WriteAsync(bytes, 0, bytes.Length);

        var response2 = await httpWebRequest_0.GetResponseAsync();

        using (StreamReader reader = new StreamReader(response2.GetResponseStream()))
        {
            finalStr = reader.ReadToEnd();
        }

        if (finalStr.Contains(handle))
        {
            return "success";
        }
        else
        {
            requestStream.Close();
            return "error";
        }
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message);
    }
}

I believe it's this part of the function:

HttpWebRequest httpWebRequest_0 = (HttpWebRequest)WebRequest.Create("https://url.com");

How could I create a async WebRequest.Create? Is there something else I'm doing wrong?

I appreciate any kind of help and suggestions.

Answer 1

Since WebRequest.Create uses Dns.GetHostByName internally which is a blocking method (and sometimes really slow) your code can be blocked at that point.

A simple workaround can be creating a task and awating it

HttpWebRequest request = await Task.Run(()=> WebRequest.Create("https://google.com") as HttpWebRequest);

Answer 2

I would suggest switching to HttpClient as the recommended client moving forward. (Thanks for the reminder Erik)

This will need some updates to fit your needs but it is a starting point for making the transition.

            using (var client = new HttpClient(new HttpClientHandler
            {
                AllowAutoRedirect = true,
                CookieContainer = new CookieContainer()
            }))
            {
                client.DefaultRequestHeaders.Clear();
                client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8"));
                client.DefaultRequestHeaders.Referrer = new Uri("https://twitter.com/settings/account");
                client.DefaultRequestHeaders.UserAgent.ParseAdd("Mozilla/5.0 (Windows NT 6.1) AppleWebKit/535.2 (KHTML, like Gecko) Chrome/15.0.874.121 Safari/535.2");

                // Get
                var result = await client.GetAsync(new Uri(""));
                if (result.IsSuccessStatusCode)
                {
                    var content = await result.Content.ReadAsStringAsync();
                }
                else
                {
                    Console.WriteLine($"{result.StatusCode}: {await result.Content.ReadAsStringAsync()}");
                }

                // Post
                var post = await client.PostAsync("Uri", new StringContent("could be serialized json or you can explore other content options"));
                if (post.IsSuccessStatusCode)
                {
                    var contentStream = await post.Content.ReadAsStreamAsync();
                    var contentString = await post.Content.ReadAsStringAsync();
                }
            }

Answer 3

you can convert any piece of code into async code by using

Task.Run(()=>{
  //any code here...
});

but i think as long as your entry method is async then everything under that runs in async with reference to the code calling that method.

public async Task<string> function(string username, string password, string handle)

should therefore be running without blocking your UI cuz you are not expected to convert everthing to be async.

please also check when you are calling this "function" you are using async/await over there. if you have resharper, that will generally tell you when you are missing async/await in such scenario, because without that you could be calling your method synchronously.