UI hangs when using threads C#

Question

I am using multithreading to do some tasks but when I start the process, the UI hangs, I am using the same method in another solution and its working fine!

Here is a snippet. I tried to use HTMLagality as well, but I don't think this is the reason, this method uses the normal http web request

Using C#, VS 2015, .Net Framework 4.6.1

 var th = new Thread(() =>
            {
                if (LinksToGetEmailsListView.InvokeRequired)
                {
                    LinksToGetEmailsListView.Invoke((MethodInvoker)delegate ()
                    {
                        foreach (ListViewItem link in LinksToGetEmailsListView.Items)
                        {       
                            #region Extracting Emails from Html Page
                            //instantiate with this pattern 

                            HttpWebRequest httpWebRequest = (HttpWebRequest)WebRequest.Create(link.Text);
                            httpWebRequest.UseDefaultCredentials = true;
                            httpWebRequest.UserAgent = @"Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.2; Trident/6.0)";

                            httpWebRequest.Method = WebRequestMethods.Http.Get;
                            httpWebRequest.Accept = "application/json; charset=utf-8";

                            string file;
                            var response = (HttpWebResponse)httpWebRequest.GetResponse();
                            using (var sr = new StreamReader(response.GetResponseStream()))
                            {
                                file = sr.ReadToEnd();
                            }


                            string[] result = GetEmailsFromWebContent(file);
                            foreach (string r in result)
                            {
                                XtraMessageBox.Show(r);
                            }
                            #endregion






                            //   string[] result = GetEmailsFromWebContent(iWeb.Load(link.Text).DocumentNode.OuterHtml);
                            link.Focused = true;
                           // foreach (string email in result)
                            //{
                 //               XtraMessageBox.Show(email);
                            //}

                        }
                    });
                }
                else
                {
                    foreach (ListViewItem link in LinksToGetEmailsListView.Items)
                    {

                        #region Extracting Emails from Html Page
                        //instantiate with this pattern 

                        HttpWebRequest httpWebRequest = (HttpWebRequest)WebRequest.Create(link.Text);
                        httpWebRequest.UseDefaultCredentials = true;
                        httpWebRequest.UserAgent = @"Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.2; Trident/6.0)";

                        httpWebRequest.Method = WebRequestMethods.Http.Get;
                        httpWebRequest.Accept = "application/json; charset=utf-8";

                        string file;
                        var response = (HttpWebResponse)httpWebRequest.GetResponse();
                        using (var sr = new StreamReader(response.GetResponseStream()))
                        {
                            file = sr.ReadToEnd();
                        }


                        string[] result = GetEmailsFromWebContent(file);
                        foreach (string r in result)
                        {
                            XtraMessageBox.Show(r);
                        }
                        #endregion
                    }

                }


            });
            th.SetApartmentState(ApartmentState.STA);
            th.Start();

There is what we call UI Thread where all UI-related behaviors should be placed. On your sample code you are creating a new thread and you're trying to perform UI-related actions such as XtraMessageBox.Show(r);. Make sure that it runs on the UI thread instead. Try looking up on how to invoke to the UI thread. — jegtugado
– jegtugado, Commented Feb 4, 2019 at 9:00
I already removed XtraMessagebox from the thread and it didn't solve it ! — JamesRick
– JamesRick, Commented Feb 4, 2019 at 9:02
This is way too much code to post. Try to be concise and only post the Code that actually gives you trouble. It makes the entire thing a lot easier for us to read and understand — MindSwipe
– MindSwipe, Commented Feb 4, 2019 at 9:03

Marc Gravell · Accepted Answer · 2019-02-04 09:03:28Z

4

You're actually running all that code on the UI thread, which is why the UI is hanging. You start a secondary thread, but then you immediately do a InvokeRequired / Invoke check. Well; it will be required, because you're on a secondary thread. So... the first thing you do in your secondary thread is push the work right back to the UI thread.

You probably wanted to defer the Invoke until you're actually ready to update the UI, i.e. around the final XtraMessageBox.Show (and possibly the foreach around that). And importantly: remove it from earlier in the method.

answered Feb 4, 2019 at 9:03

Marc Gravell

1.1m273 gold badges2.6k silver badges3k bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

JamesRick Over a year ago

when I removed the http web request the UI didn't hang up ! do you have any idea how I can fix that ! I already removed XtraMessage

Marc Gravell Over a year ago

@JamesRick like I said: get rid of the premature InvokeRequired / Invoke, so that you aren't doing the http on the UI thread; move the Invoke lower down, when you're actually ready to update the UI

Collectives™ on Stack Overflow

UI hangs when using threads C#

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related