更改文件名后出现错误

更改文件名后出现几个错误。从默认表单名称（Form2.cs），（Form1.cs）等到System.cs，LoginPage.cs，当我改回默认表单名称（Form2.cs）时，会发生这种情况，并出现错误。我该怎么办？有什么解决方案可以将这个问题恢复到更改文件名之前的时间吗？

这是“ Form1.cs”的完整代码：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Globalization;
using System.Data.OleDb;
using System.Security.Principal;

namespace Sell_System
{
    public partial class Form1 : Form
    {
        string connectionString = (@"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=\Archives\Projects\Program\Sell System\Sell System\App_Data\db1.accdb;Persist Security Info=False;");

        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            label4.Visible = false;
            comboBox1.Items.Add("English");
            comboBox1.Items.Add("Indonesian");
            comboBox1.SelectedIndex = 0;

            OleDbDataReader dReader;
            OleDbConnection conn = new OleDbConnection(connectionString);
            conn.Open();
            OleDbCommand cmd = new OleDbCommand("SELECT DISTINCT [Username] FROM [Member]", conn); 
            dReader = cmd.ExecuteReader();
            AutoCompleteStringCollection namesCollection = new AutoCompleteStringCollection();

            while (dReader.Read())
            {
               namesCollection.Add(dReader.GetString(0));
            }

            textBox1.AutoCompleteMode = AutoCompleteMode.Suggest;
            textBox1.AutoCompleteSource = AutoCompleteSource.CustomSource;
            textBox1.AutoCompleteCustomSource = namesCollection;

            dReader.Close();
            conn.Close();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            OleDbConnection conn = new OleDbConnection(connectionString);

            conn.Open();

            DataTable dt = new DataTable();

            OleDbCommand cmd = new OleDbCommand("SELECT * FROM [Member] WHERE [Username]='" + textBox1.Text + "'AND [Password]='" + textBox2.Text + "'", conn);

            OleDbDataAdapter da = new OleDbDataAdapter(cmd);

            da.Fill(dt);

            if (dt.Rows.Count != 0)
            {
                this.Hide();

                Form2 secondaryForm = new Form2(this);
                secondaryForm.ShowDialog();

                this.Close();
            }

            else if (textBox1.Text == "Admin" && textBox2.Text == "")
            {
                this.Hide();

                Form5 fifthForm = new Form5();
                fifthForm.ShowDialog();

                this.Close();
            }

            else
            {
                label4.Visible = true;

                if (comboBox1.SelectedItem.ToString() == "English")
                {
                    RecursiveClearTextBoxes(this.Controls);
                    label4.Text = "Invalid Username or Password!";
                    label4.ForeColor = Form1.Drawing.Color.Red;
                }

                else if (comboBox1.SelectedItem.ToString() == "Indonesian")
                {
                    RecursiveClearTextBoxes(this.Controls);
                    label4.Text = "Username atau Password anda salah!";
                    label4.ForeColor = Form1.Drawing.Color.Red;
                }
            }

            conn.Close();
        }

        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            if (comboBox1.SelectedItem.ToString() == "English")
            {
                ChangeLanguage("en");
            }

            else if (comboBox1.SelectedItem.ToString() == "Indonesian")
            {
                ChangeLanguage("id");
            }
        }

        private void ChangeLanguage(string language)
        {
            foreach (Control c in this.Controls)
            {
                ComponentResourceManager resources = new ComponentResourceManager(typeof(Form1));
                resources.ApplyResources(c, c.Name, new CultureInfo(language));
            }
        }

        private void RecursiveClearTextBoxes(Control.ControlCollection cc)
        {
            foreach (Control ctrl in cc)
            {
                TextBox tb = ctrl as TextBox;

                if (tb != null)
                {
                    tb.Clear();
                }

                else
                {
                    RecursiveClearTextBoxes(ctrl.Controls);
                }
            }
        }

        private void linkLabel1_LinkClicked(object sender, LinkLabelLinkClickedEventArgs e)
        {
            this.Hide();

            Form3 thirdForm = new Form3();
            thirdForm.ShowDialog();

            this.Close();
        }

        protected virtual void ClosedHandler(object sender, EventArgs e)
        {
            FormsHandler.Remove(this);
        }

    }
}

在“ Form1.cs”上的错误是：

“ Sell_System.Form1.cs”不包含“绘图”的定义