C＃-我的项目没有从listbox1移动到listbox2

这就是我的GUI的样子

我当时正在为一个大学工作

它所做的是读取文本文件

放入listbox1

那么第二个按钮应该让成功进入listbox2的学生

但是每当我按下按钮时，我都会得到一个错误

我尽力在所有地方搜寻，但找不到问题

只是没有原因而没有在listbox2中写入它

有人知道我该怎么办？

我该怎么做才能使其正常工作？？？

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;
using System.IO;

namespace second_Project
{

    public partial class FSS : Form
    {
        private void FSS_Load(object sender, EventArgs e)
        {
        }

        public FSS()
        {
            InitializeComponent();
        }



        public class StdScore   
        {

            public int id;
            public string name;
            public double xam, Score, Pract;
            public string content;

            public string[] xx;


        }


        OpenFileDialog ofd = new OpenFileDialog();


        private void button1_Click(object sender, EventArgs e)
        {
            StdScore StdScore = new StdScore();      

            ofd.Filter = "TXT|*.txt";

            if (ofd.ShowDialog() == DialogResult.OK)
            {

                StreamReader sr = new StreamReader(ofd.FileName);


                while (!sr.EndOfStream)
                {

                    StdScore.content = sr.ReadLine();

                    string[] info = StdScore.content.Split(' ');

                    StdScore.xx = new string[info.Length];

                    listBox1.Items.Add(StdScore.content);
                  
                }
                sr.Close();
            }
        }



        private void button2_Click(object sender, EventArgs e)
        {
            StdScore StdScore = new StdScore();      


            StdScore.xam = 0;
            StdScore.Pract = 0;
            StdScore.Score = 0;

            StdScore.xam += int.Parse(StdScore.xx[2]);   

            StdScore.Pract += int.Parse(StdScore.xx[3]);  

            StdScore.Score = StdScore.xam * 0.7 + StdScore.Pract * 0.3; 



            if (StdScore.xam >= 40 && StdScore.Pract >= 40 && StdScore.Score >= 60)  
            {

                StdScore.xam = (StdScore.xam * 70) / 100;
                StdScore.Pract = (StdScore.Pract * 30) / 100;
                StdScore.Score = StdScore.xam + StdScore.Pract;

                listBox2.Items.Add(StdScore.xx[0] + " " + StdScore.xx[1] + " " + StdScore.xx[2] + " " + StdScore.xx[3] + " " + StdScore.Score + " " + "Succes");


            }

        }


    }
}