跨线程调用问题

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Linq;

using System.Text;

using System.Windows.Forms;



namespace WindowsFormsApplication1

{

    public partial class Form1 : Form

    {

        public Form1()

        {

            InitializeComponent();

        }



        public delegate void GUIDelegate(string paramString);

        BackgroundWorker bgw = new BackgroundWorker();



        private void button1_Click(object sender, EventArgs e)

        {

            bgw.DoWork += new DoWorkEventHandler(bgw_DoWork);

            bgw.WorkerSupportsCancellation = true;

            bgw.RunWorkerAsync();

            

        }



        void bgw_DoWork(object sender, DoWorkEventArgs e)

        {

            while (!bgw.CancellationPending)

            {

                DoGUIUpdate((i++).ToString());

                System.Threading.Thread.Sleep(1000);

            }

        }



        int i = 0;



        public void DoGUIUpdate(string paramString)

        {

            if (this.InvokeRequired)

            {

                GUIDelegate delegateMethod = new GUIDelegate(DoGUIUpdate);

                this.Invoke(delegateMethod, new object[] { paramString });

            }

            else

            {

                listBox1.Items.Add("the count is:" + paramString);

            }

        }

    }

}

我有点不太明白，backgroundworker算是建立了一个线程，这个时候去调用窗口上空间的线程，于是this.InvokeRequired等于true，就开始执行this.Invoke，但是他怎么执行到listBox1.Items.Add("the count is:" + paramString);这一行的，不是太明白，而且好像这样的程序没办法debug。

总结就是2个问题：

1.他怎么执行到listBox1.Items.Add("the count is:" + paramString);这一行的

2.这样的程序如何debug