多線程中使用委託和invoke方法訪問視窗

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.Windows.Forms;

namespace WindowsFormsApplication1
{

    public partial class Form1 : Form
    {
        delegate void AppendStringDelegate(string str);
        AppendStringDelegate appendStringDelegate;
        public Form1()
        {
            InitializeComponent();
            appendStringDelegate = new AppendStringDelegate(AppendString);

        }
     
        public StringBuilder sb = new StringBuilder();
        Thread thread1;
        Thread thread2;

        private void AppendString(string s)
        {
            richTextBox1.Text += s;
        }

        public void Method1()
        {
            while (true)
            {
                Thread.Sleep(100);
                richTextBox1.Invoke(appendStringDelegate, "a");
            }
       
        }

        public void Method2()
        {
            while (true)
            {
                Thread.Sleep(100);
                richTextBox1.Invoke(appendStringDelegate, "b");
            }

        }

 

        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void button1_Click(object sender, EventArgs e)
        {
            richTextBox1.Text = "";
            thread1 = new Thread(new ThreadStart(Method1));
            thread2 = new Thread(new ThreadStart(Method2));
            thread1.Start();
            thread2.Start();
        }

        private void button2_Click(object sender, EventArgs e)
        {
            thread1.Abort();
            thread1.Join(10);
            thread2.Abort();
            thread2.Join(10);
            MessageBox.Show("線程1、2終止成功");
        }

    
    }
}