public class Test
    {
        int _index = 0;
        Thread _thread;
        public int Index
        {
            get { return _index; }
            set { _index = value; }
        }
        public Thread Thread
        {
            get { return _thread; }
            set { _thread = value; }
        }
        public void Run()
        {
            string result = DateTime.Now.ToString("HH:mm:ss:fff") + "  " + _thread.ManagedThreadId.ToString("00") + " is " + _thread.IsAlive.ToString() + ":" + _index.ToString();
            try
            {
                File.AppendAllText("result.txt", result + "\r\n");
            }
            catch (Exception ex)
            {
                File.AppendAllText("result_failed.txt", result + "    " + ex.Message + "\r\n");
            }
            //请问在这里如何给textBox1.Text赋值 result 呢：（
            //想实现每一个进程执行完后都在textBox1.Text中输出 result 结果
        }
    }

using System;
using System.IO;
using System.Threading;
using System.Windows.Forms;

namespace 多线程操作FORM
{
    public delegate void ChangeTextBox(string text);
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        private void button1_Click(object sender, EventArgs e)
        {
            for (int i = 0; i < 24; i++)
            {
                Test test = new Test();
                test.Index = i;
                test.WorkCompleted += new EventHandler(test_WorkCompleted);
                Thread thread = new Thread(new ThreadStart(test.Run));
                thread.IsBackground = true;
                test.Thread = thread;
                thread.Start();
                //Thread.Sleep(1);
            }
            //textBox1.Text = "完成";
        }

        void test_WorkCompleted(object sender, EventArgs e)
        {
            int i = ((Test)sender).Index;
            if (this.InvokeRequired)
            {
                this.Invoke(new ChangeTextBox(ChangeTextBoxMethod), i.ToString());
            }
            else
            {
                ChangeTextBoxMethod(i.ToString());
            }
        }

        private void ChangeTextBoxMethod(string value)
        {
            textBox1.Text += string.Format("Work {0} done.{1}", value, Environment.NewLine);
        }
    }
    public class Test
    {
        int _index = 0;
        Thread _thread;
        public event EventHandler WorkCompleted;
        public int Index
        {
            get { return _index; }
            set { _index = value; }
        }
        public Thread Thread
        {
            get { return _thread; }
            set { _thread = value; }
        }
        public void Run()
        {
            string result = DateTime.Now.ToString("HH:mm:ss:fff") + "  " + _thread.ManagedThreadId.ToString("00") + " is " + _thread.IsAlive.ToString() + ":" + _index.ToString();
            try
            {
                File.AppendAllText("result.txt", result + "\r\n");
            }
            catch (Exception ex)
            {
                File.AppendAllText(string.Format("result{0}_failed.txt", Index.ToString()), result + "    " + ex.Message + "\r\n");
            }
            if (WorkCompleted != null)
            {
                WorkCompleted(this, EventArgs.Empty);
            }
            //请问在这里如何给textBox1.Text赋值 result 呢：（
            //想实现每一个进程执行完后都在textBox1.Text中输出 result 结果
        }
    }
}