How can I correct the error "accessed from a thread other than the thread it was created on"?

Question

This following code gives me the error below . I think I need "InvokeRequired" . But I don't understand how can I use?

Cross-thread operation not valid: Control 'listBox1' accessed from a thread other than the thread it was created on.

The code:

using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Threading;

namespace WindowsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        protected static DataSet dataset = null;
        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void timer1_Tick(object sender, EventArgs e)
        {
            SimulationFrameWork.MCSDirector run = new SimulationFrameWork.MCSDirector();
            DataSet ds = run.Get();

            if (ds.Tables[0].Rows.Count > 0)
            {
                for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
                {
                    if (ds.Tables[0].Rows[i]["result"].ToString() == "0")
                    {
                       dataset = run.Get(int.Parse(ds.Tables[0].Rows[i]["ID"].ToString()));
                       WorkerObject worker = 
                         new WorkerObject(
                           int.Parse(dataset.Tables[0].Rows[i]["ID"].ToString()),
                           int.Parse(dataset.Tables[0].Rows[i]["Iteration"].ToString()),
                           listBox1, timer1);
                       Thread thread1 = new Thread(new ThreadStart(worker.start));
                       thread1.Start();
                    }
                }
            }
        }
    }

    public class WorkerObject
    {
        private int id;
        private int nmax;
        private ListBox list1;
        private System.Windows.Forms.Timer timer1;

        public WorkerObject(int _id, int _nmax, ListBox _list1, 
                            System.Windows.Forms.Timer _timer1)
        {
            id = _id;
            nmax = _nmax;
            list1 = _list1;
            timer1 = _timer1;
        }
        public void start()
        {
            timer1.Stop();
            int i, idaire, j;
            double pi = 0.0, x, y;

            Random rnd = new Random();
            for (i = 0; i < 100; i++)
            {
                idaire = 0;
                for (j = 0; j < nmax; j++)
                {
                    x = rnd.Next(1, 10000) / (double)10000;
                    y = rnd.Next(1, 10000) / (double)10000;
                    if (Math.Pow(x, 2) + Math.Pow(y, 2) <= 1.0)
                        idaire += 1;
                }
                pi = 4 * (double)idaire / (double)nmax;
                nmax *= 10;

                list1.Items.Add(
                  "Iterasyon:" + 
                  nmax.ToString() + 
                  " ----->" + 
                  pi.ToString() + 
                  "\n");
                System.Threading.Thread.Sleep(100);
            }
            SimulationFrameWork.MCSDirector run = new SimulationFrameWork.MCSDirector();
            run.Update(id, pi);
            list1.Items.Add("\n\n islem bitti...");
        }
    }
}

Answer 1

This should get you around it

private delegate void stringDelegate(string s);
private void AddItem(string s)
{
    if (list1.InvokeRequired)
    {
        stringDelegate sd = new stringDelegate(AddItem);
        this.Invoke(sd, new object[] { s });
    }
    else
    {
        list1.Items.Add(s);
    }
}

Just call AddItem and this will invoke the add using a delegate if it is required otherwise it will just add the item directly to the box.

OneSHOT

Answer 2

Just encapsulate adding the text to the listbox to another method:

private void timer1_Tick(object sender, EventArgs e)
{
   // ...
   AddTextToListBox("\n\n işlem bitti...");
}

private void AddTextToListBox(string text)
{
   if(list1.InvokeRequired)
   {
      list1.Invoke(new MethodInvoker(AddTextToListBox), new object[] { text }); 
      return;
   }

   list1.Items.Add(text);
}