C# 迴圈時，操作另外一個程式直到操作完成，迴圈繼續執行

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

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

        static EventWaitHandle eHandle = new EventWaitHandle(false, EventResetMode.ManualReset);
        bool flag = false;

        private void button1_Click(object sender, EventArgs e)
        {
            richTextBox1.Clear();
            for (int i = 1; i <= 100; i++) {
                richTextBox1.AppendText(i + "
");
                if (i % 10 == 0) {
                    eHandle = new EventWaitHandle(false, EventResetMode.ManualReset);
                    Thread currentThread = new Thread(new ThreadStart(TestProcess));//開闢一個進度條執行緒
                    currentThread.Start();
                    eHandle.WaitOne();
                    richTextBox1.AppendText("i是10的倍數: i = " + i + "
");
                    if (flag == true)
                    {
                        richTextBox1.AppendText("程式結束" + "
");
                        break;
                    }
                }
            }
        }


        private void TestProcess() {
            if (MessageBox.Show("確定要退出嗎？", "Message", MessageBoxButtons.OKCancel, MessageBoxIcon.Question) == DialogResult.Cancel)
            {
                flag = false;
            }
            else
            {
                flag = true;
            }
            eHandle.Set();
        }

        private void richTextBox1_TextChanged(object sender, EventArgs e)
        {
            richTextBox1.SelectionStart = richTextBox1.Text.Length;
            richTextBox1.ScrollToCaret();
        }
    }
}