Csharp読み書きファイル内容検索自動ポップアップAutoCompleteMode

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.IO;

namespace WindowsFormsStyle
{
    public partial class LoginForm : Form
    {
        protected string fileName = "login.dat";
        string path = Directory.GetCurrentDirectory();
        string file;
        /// <summary>
        /// 
        /// </summary>
        public LoginForm()
        {
            InitializeComponent();
        }
        /// <summary>
        /// 2011-11-2  
        ///  
        ///  
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void LoginForm_Load(object sender, EventArgs e)
        {
            file = path + "\\" + fileName;

            textBox1.AutoCompleteMode = AutoCompleteMode.SuggestAppend;
            textBox1.AutoCompleteSource = AutoCompleteSource.CustomSource;
            if (File.Exists(file))// 
            {
                StreamReader sr = new StreamReader(file, true);
                string str = sr.ReadLine();
                while (str != null) // 
                {
                    if (!this.textBox1.AutoCompleteCustomSource.Contains(str))// 
                    {
                        this.textBox1.AutoCompleteCustomSource.Add(str);// 
                    }
                    str = sr.ReadLine();
                }
                sr.Close();
            }
        }
        /// <summary>
        ///  
        ///  
        ///  
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void button1_Click(object sender, EventArgs e)
        {
            file = path + "\\" + fileName;
            textBox1.AutoCompleteMode = AutoCompleteMode.SuggestAppend;
            textBox1.AutoCompleteSource = AutoCompleteSource.CustomSource;
            if (File.Exists(file))
            {
               if(!this.textBox1.AutoCompleteCustomSource.Contains(this.textBox1.Text.Trim()))// 
               {
                   StreamWriter sw=new StreamWriter(file,true);
                   sw.WriteLine(this.textBox1.Text.Trim()); // 
                   sw.Close();// 
                   if(!this.textBox1.AutoCompleteCustomSource.Contains(this.textBox1.Text))
                   {
                       this.textBox1.AutoCompleteCustomSource.Add(this.textBox1.Text);
                   }
               }
            }
            this.Close();

        }
    }
}