C# - Program Freeze

Question

I made proxy checker, and for some reason when I click the "Check" button, the program just freeze until the work is done.

I tried to move the code to Backgroundworker:

private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
    {
        WebProxy myproxy;
        foreach (string proxy in Proxies)
        {
            try
            {
                myproxy = new WebProxy(proxy);
                WebRequest request = WebRequest.Create("https://www.google.co.il/");
                request.Timeout = TimeOut;
                request.Proxy = myproxy;
                WebResponse re = request.GetResponse();
                richTextBox1.AppendText(proxy + "\r\n");
                Good++;
                label3.Text = "Good: " + Good.ToString();
            }
            catch (Exception)
            {
                Bad++;
                label4.Text = "Bad: " + Bad.ToString();
            }
        }
        MessageBox.Show("Done");
    }

but for some reason I get this error:

System.InvalidOperationException: 'Cross-thread operation not valid: Control 'richTextBox1' accessed from a thread other than the thread it was created on.'

so I tried to remove the label3.Text and label4.Text. but then I saw that nothing happen when I click the "Check" Button.

so I tried to add MessageBox.Show("some text") to see if it's working, I saw the messagebox but it looks like the Thread skip the check.

what can I do?

"Check" button code:

 label1.Text = "Lines: 0";
        richTextBox1.Clear();
        backgroundWorker1.RunWorkerAsync();

The full code:

 public partial class Form1 : Form
{
    WebClient X = new WebClient();
    string url = "";
    ArrayList Proxies = new ArrayList();
    int TimeOut = 3000, Good = 0, Bad = 0;

    public Form1()
    {
        InitializeComponent();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        try
        {
            if (radioHTTP.Checked)
            {
                byte[] proxies = X.DownloadData(new Uri("https://www.free-proxy-list.net/"));
                MatchCollection M = Regex.Matches(Encoding.UTF8.GetString(proxies, 0, proxies.Length), "\\d{1,3}[.]\\d{1,3}[.]\\d{1,3}[.]\\d{1,3}</td><td>\\d{1,6}");
                foreach (Match m in M)
                    richTextBox1.AppendText(m.Value.Replace("</td><td>", ":") + "\r\n");
            }
            if (radioSocks.Checked)
            {
                byte[] proxies = X.DownloadData(new Uri("https://www.socks-proxy.net/"));
                MatchCollection M = Regex.Matches(Encoding.UTF8.GetString(proxies, 0, proxies.Length), "\\d{1,3}[.]\\d{1,3}[.]\\d{1,3}[.]\\d{1,3}</td><td>\\d{1,6}");
                foreach (Match m in M)
                    richTextBox1.AppendText(m.Value.Replace("</td><td>", ":") + "\r\n");
            }
            if (radioSSL.Checked)
            {
                byte[] proxies = X.DownloadData(new Uri("https://www.sslproxies.org/"));
                MatchCollection M = Regex.Matches(Encoding.UTF8.GetString(proxies, 0, proxies.Length), "\\d{1,3}[.]\\d{1,3}[.]\\d{1,3}[.]\\d{1,3}</td><td>\\d{1,6}");
                foreach (Match m in M)
                    richTextBox1.AppendText(m.Value.Replace("</td><td>", ":") + "\r\n");
            }
            if (radioCustom.Checked)
            {
                byte[] proxies = X.DownloadData(new Uri(url));
                MatchCollection A = Regex.Matches(Encoding.UTF8.GetString(proxies, 0, proxies.Length), "\\d{1,3}[.]\\d{1,3}[.]\\d{1,3}[.]\\d{1,3}</td><td>\\d{1,6}");
                MatchCollection B = Regex.Matches(Encoding.UTF8.GetString(proxies, 0, proxies.Length), "\\d{1,3}[.]\\d{1,3}[.]\\d{1,3}[.]\\d{1,3}\\d{1,6}");
                MatchCollection C = Regex.Matches(Encoding.UTF8.GetString(proxies, 0, proxies.Length), "\\d{1,3}[.]\\d{1,3}[.]\\d{1,3}[.]\\d{1,3}\",\"port\":\"\\d{2,6}");
                MatchCollection D = Regex.Matches(Encoding.UTF8.GetString(proxies, 0, proxies.Length), "\\d{1,3}[.]\\d{1,3}[.]\\d{1,3}[.]\\d{1,3}</td><td class=\"column-2\">\\d{2,6}");
                foreach (Match m in A)
                    richTextBox1.AppendText(m.Value.Replace("</td><td>", ":") + "\r\n");
                foreach (Match m in B)
                    richTextBox1.AppendText(m.Value + "\r\n");
                foreach (Match m in C)
                    richTextBox2.AppendText(m.Value.Replace("\",\"port\":\"", ":") + "\r\n");
                foreach (Match m in D)
                    richTextBox2.AppendText(m.Value.Replace("</td><td class=\"column-2\">", ":") + "\r\n");
            }
            string[] lines = richTextBox1.Lines;
            foreach (string line in lines)
                Proxies.Add(line);
            label1.Text = "Lines: " + Proxies.Count;
        }catch
        {

        }

    }
    private void button4_Click(object sender, EventArgs e)
    {
        label1.Text = "Lines: 0";
        richTextBox1.Clear();
        backgroundWorker1.RunWorkerAsync();
    }
    private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
    {
        // backgroundWorker1.ReportProgress(0, "Working...");
        WebProxy myproxy;
        foreach (string proxy in Proxies)
        {
            try
            {
                myproxy = new WebProxy(proxy);
                WebRequest request = WebRequest.Create("https://www.google.co.il/");
                request.Timeout = TimeOut;
                request.Proxy = myproxy;
                WebResponse re = request.GetResponse();
                richTextBox1.AppendText(proxy + "\r\n");
                Good++;
                this.Invoke((Action)delegate {
                    label3.Text = "Good: " + Good.ToString();
                });
            }
            catch (Exception)
            {
                Bad++;
                this.Invoke((Action)delegate {
                    label4.Text = "Bad: " + Good.ToString();
                });
            }
        }
        //backgroundWorker1.ReportProgress(100, "Done");
    }

Thank you very much

Answer 1

WinForms controls cannot be modified outside of the thread they were created in.

So doing something like this:

label3.Text = "Good: " + Good.ToString();

Will fail in a background worker as background worker tasks are run in a separate thread.

To get around this you can invoke a delegate on the form's thread like so:

this.Invoke((Action) delegate {
    label3.Text = "Good: " + Good.ToString();
});

Using the invoke function will force the code to run on the same thread as the form's UI.