updating listbox from separate thread c#

Question

So I am trying to update a listbox from some data I'm receiving over my local network.

I know there is something fundamental I'm missing. Could anyone explain what I might be doing wrong here? I realize that you cannot update UI from any thread other than the UI thread. I guess my issue is that I do not know how to specify that I want the UI thread to update the values.

You can see in the monitor thread what I am trying to accomplish.

namespace FrontEnd
{
    public partial class Form1 : Form
    {
        TcpClient clientSocket = new TcpClient();
        //CommandQueue commandqueue;
        private List<String> COMMANDS = new List<String>();
        private object m_lock = new object();
        delegate void AddListItemDelegate(string text);

        public void enqueue(string command)
        {
            lock (m_lock)
            {
                Debug.WriteLine("Enqueue");
                COMMANDS.Add(command);
            }
        }

        public string dequeue()
        {
            lock (m_lock)
            {
                string tmp = COMMANDS.First();
                COMMANDS.RemoveAt(0);
                return tmp;
            }
        }


        public void monitor()
        { // need a better mechanism

            while (true)
            { // bad algorithm
                lock (m_lock)
                {
                    if (COMMANDS.ToArray().Length > 0)
                    { // if queue is not empty
                        do
                        { // this is okay
                            string dequeued = dequeue();
                            string command = dequeued.Split(':')[0];
                            string data = dequeued.Split(':')[1];
                            if (command.Equals("add"))
                            { // add student
                                Debug.WriteLine("adding item to listbox");

                                //lbStudents.Items.Add(data);
                                //lbStudents.Update();
                            }
                        } while (COMMANDS.ToArray().Length > 0);
                    }
                }
            }
        }

        public Form1()
        {
            InitializeComponent();
        }
        public void launchThread()
        {

            Form1 f1 = new Form1();
                        Thread oThread = new Thread(monitor);
            oThread.Start(f1);
            while (!oThread.IsAlive) ;
            Debug.WriteLine("THREAD LAUNCHED");
        }

        private void cleanResponse(string response)
        {
            string[] responses = response.Split(':');
            string command = responses[0];
            string[] data = responses.ToList().GetRange(1, responses.Length - 2).ToArray();
            for (int i=0;i<data.Length;i++)
            {
                Debug.WriteLine("thing in here debug");
                try
                {
                    enqueue(command + ':' + data[i]);
                }
                catch (Exception e)
                {
                    Debug.WriteLine("EXCEPTION: " + e);
                }
            }
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            launchThread();
            lblStatus.Text = "Connecting...";
            clientSocket.Connect("10.108.45.120", 9001);
            Stream stm = clientSocket.GetStream();
            byte[] ba = new ASCIIEncoding().GetBytes("start");
            stm.Write(ba, 0, ba.Length);
            byte[] bb = new byte[100];
            lblStatus.Text = "Connected!";
            stm.Read(bb, 0, bb.Length);
            string response = System.Text.ASCIIEncoding.UTF8.GetString(bb);
            cleanResponse(response);
            clientSocket.Close();
            grpbxSparseMatrix.ForeColor = Color.White;
        }
    }
}

Answer 1

Use BeginInvoke from the non-UI thread.

Action<string> add = str => {
    lbStudents.Items.Add(str);
}

BeginInvoke(add, data);