C#試寫一個多線程問題（委託，Invoke（），beginInvoke（））

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

namespace _
{
    public partial class Form1 : Form
    {
        public delegate void del(string str);
        public delegate void del1(string str1);
        Thread thread1,thread2;
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            this.thread1 = new Thread(new ThreadStart(this.sa));
            this.thread1.Start();
            //MessageBox.Show(this,);
            this.button1.Enabled = false;
            //擷取當前的線程好
            int thread1id = Thread.CurrentThread.GetHashCode();
            string strThreadId = Convert.ToString(thread1id);
            MessageBox.Show(this,strThreadId);
        }       

        private void progressSet(string text)
        {
                progressBar1.Value = 0;
                progressBar1.Maximum = 999999;
                for (int i = 0; i < 999999; i++)
                {
                    progressBar1.Value++;
                }
                progressBar1.Value = 0;           
        }

        private void sa()
        {
            del pro = new del(progressSet);
            this.Invoke(pro, new object[] { "hello" });
        }

        private void button2_Click(object sender, EventArgs e)
        {
            this.thread2 = new Thread(this.sa1);
            thread2.Start();
            this.button2.Enabled = false;
            //擷取當前的線程好
            int thread2id = Thread.CurrentThread.GetHashCode();
            string strThreadId = Convert.ToString(thread2id);
            MessageBox.Show(this, strThreadId);
        }

        private void sa1()
        {
            //其他動作
            //比如將介面的TextBox內容設定一下
            del1 mi1 = new del1(UpdateTextBox);
            this.Invoke(mi1, new object[] { "我是一個文字框" });
        }

        //更新介面的方法
        private void UpdateTextBox(string str)
        {
            //更新
            this.textBox1.Text = str;
        }
    }
}