问For循环停止在列表框中的第一项之后迭代

EN

for(int i = 0; i < listBox8.Items.Count; i++) {
    listBox8.SetSelected(i, true);
    listBox8.SelectedIndex = 0;

    Thread t = new Thread(signinmobile);
    t.Start();
    CheckForIllegalCrossThreadCalls = false;
}

public void signinmobile()
{
    string yourString = listBox8.SelectedItem.ToString();
    string[] strArray = yourString.Split(':');

    System.Net.ServicePointManager.Expect100Continue = false;
    string postData = "authenticity_token=401538d41ace8f334c3d&username=" + strArray[0] + "&password=" + strArray[1] + "";
    CookieContainer tempCookies = new CookieContainer();
    UTF8Encoding encoding = new UTF8Encoding();
    byte[] byteData = encoding.GetBytes(postData);

    HttpWebRequest postReq = (HttpWebRequest)WebRequest.Create("https://mobile.twitter.com/session");
    postReq.Method = "POST";
    postReq.KeepAlive = true;
    postReq.CookieContainer = tempCookies;
    postReq.ContentType = "application/x-www-form-urlencoded";
    postReq.Referer = "https://mobile.twitter.com/session";
    postReq.UserAgent = "Mozilla/5.0 (Windows; U; Windows NT 6.1; ru; rv:1.9.2.3) Gecko/20100401 Firefox/4.0 (.NET CLR 3.5.30729)";
    postReq.ContentLength = byteData.Length;

    Stream postreqstream = postReq.GetRequestStream();
    postreqstream.Write(byteData, 0, byteData.Length);
    postreqstream.Close();
    HttpWebResponse postresponse = default(HttpWebResponse);

    postresponse = (HttpWebResponse)postReq.GetResponse();
    tempCookies.Add(postresponse.Cookies);
    StreamReader postreqreader = new StreamReader(postresponse.GetResponseStream());

    string accountstatus = postreqreader.ReadToEnd();

    webBrowser1.DocumentText = accountstatus;

    if (accountstatus.Contains("Sign in information is not correct"))
    {
        listBox9.Items.Add(listBox8.SelectedItem.ToString() + "\r");
        while (listBox8.SelectedItems.Count > 0)
        {
            listBox8.Items.Remove(listBox8.SelectedItems[0]);
        }
    }
    else
    {
        listBox2.Items.Add(listBox8.SelectedItem.ToString() + "\r");

        while (listBox8.SelectedItems.Count > 0)
        {
            listBox8.Items.Remove(listBox8.SelectedItems[0]);
        }
    }
}