C#关于Textbox滚动显示最后一行,不闪烁问题

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
 
namespace AliWorkbenchProgram
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        int y = 0;
 
        private void button1_Click(object sender, EventArgs e)
        {
            showmessage();
        }
 
        public void showmessage()
        {
            y++;
            string msg= "";
            for (int i=0;i<5000; i++)
            {
               msg = "【第" + y.ToString() + "运行】"+"序号： " +i.ToString() + "\r\n";//改变文本内容
             //this.textBox1.Text += msg  ;//改变文本内容
 
               this.textBox1.AppendText(msg);//追加文本
 
               this.textBox1.SelectionStart = this.textBox1.Text.Length;
               this.textBox1.ScrollToCaret();//滚动到最后一行
 
            }
 
        }
 
 
    }
}

        /// <summary>
        /// textBox多行文本框，自动滚动到最后一行
        /// </summary>
        /// <param name="msg"></param>
        public void add_textbox_msg(string msg)
        {
            //容错处理
            if (string.IsNullOrEmpty(msg))
            {
                return;
            }
            textBox1.AppendText(msg);
            textBox1.AppendText("\r\n");//换行
            textBox1.ScrollToCaret();
        }