C#(winform) 操作.txt文本的例子

背景：一个可输入textbox，可以实现搜索功能
功能改进需求：把textbox改造成一个可输入的下拉框,下拉框的内容是历史搜索记录(最近20次输入搜索的内容)

代码：

using System.IO;
using System.Text.RegularExpressions;

   private ArrayList _arrSearchHistory = null; // 全局变量  form_load时读取.txt文本中的内容

   // 放在form_load中
   ReadTxtFile(out _arrSearchHistory);
   if (_arrSearchHistory != null && _arrSearchHistory.Count > 0)
   {
   	SetComboList(cboFilter, _arrSearchHistory, null, "", false, true);
   }

   // 加到搜索功能中
   if (!string.IsNullOrEmpty(cboFilter.Text) && cboFilter.Text.Trim().Length>1)
   {
        AddItemToTxt(System.Windows.Forms.Application.StartupPath.Replace(@"bin\Debug", "") + "/Data/SearchHistory.txt", cboFilter.Text,out _arrSearchHistory);
   }
 
   //公共函数部分
        private void ReadTxtFile(out ArrayList arrFile,int iTopRow=20)
        {
            arrFile = new ArrayList();
            try
            {
                string sFileFullName = System.Windows.Forms.Application.StartupPath.Replace(@"bin\Debug", "") + @"/Data";
                if (!System.IO.Directory.Exists(sFileFullName))
                {
                    System.IO.Directory.CreateDirectory(sFileFullName);
                }

                sFileFullName += @"/SearchHistory.txt";
                if (!System.IO.File.Exists(sFileFullName))
                {
                    //System.IO.File.CreateText(sFileName);
                    FileStream fs;
                    fs = File.Create(sFileFullName);
                    fs.Close();
                }

                FileStream fsTxtFile = new FileStream(sFileFullName, FileMode.Open, FileAccess.Read);
                StreamReader sr = new StreamReader(fsTxtFile, System.Text.Encoding.Default);
                string sTemp;

                sTemp = sr.ReadLine();
                int iTempRow=0;
                while (!string.IsNullOrEmpty(sTemp))
                {
                    iTempRow++;
                    if (iTempRow > iTopRow)
                    {
                        break;
                    }
                    arrFile.Add(sTemp);
                    sTemp = sr.ReadLine();
                }

                sr.Close();
                sr.Dispose();
                fsTxtFile.Dispose();
            }
            catch (Exception ex)
            {
                Common.DisplayMsg(this.Text, ex.Message.ToString());
            }
        }

        /// <summary>
        /// 计算字符串中子串出现的次数
        /// </summary>
        /// <param name="str">字符串</param>
        /// <param name="substring">子串</param>
        /// <returns>出现的次数</returns>
        public  static int SubstringCount(string str, string substring)
        {
            if (str.Contains(substring))
            {
                string strReplaced = str.Replace(substring, "");
                return (str.Length - strReplaced.Length) / substring.Length;
            }

            return 0;
        }

        private void AddItemToTxt(string sFileFullName, string sNewItem,out ArrayList arrFile)
        {
            arrFile = _arrSearchHistory;

            try
            {
                string sTemp="";
                using (StreamReader sr = new StreamReader(sFileFullName))
                {
                    sr.BaseStream.Flush();
                    sTemp = sr.ReadToEnd();

                    int iCount = SubstringCount(sTemp, "\r\n");
                    if (iCount > 20)
                    {
                        Regex reg = new Regex("\r\n");
                        Match mat = reg.Match(sTemp);
                        int iCountTemp = 0;
                        while (mat.Success)
                        {
                            iCountTemp++;
                            //MessageBox.Show(mat.Index.ToString());//位置
                            if (iCountTemp > 20)
                            {
                                sTemp = sTemp.Substring(0, mat.Index);
                                break;
                            }
                            mat = reg.Match(sTemp, mat.Index + mat.Length);
                        }
                    }
                }

                //if (File.Exists(sFileFullName))
                //{
                //    File.Delete(sFileFullName);
                //}
 
                FileStream fsTxtWrite = new FileStream(sFileFullName, FileMode.Create, FileAccess.Write);
                StreamWriter srWrite = new StreamWriter(fsTxtWrite, System.Text.Encoding.UTF8);
                //StreamWriter srWrite = new StreamWriter(fsTxtWrite, System.Text.Encoding.Default);
                if (!sTemp.Contains(sNewItem))
                {
                    arrFile.Insert(0, sNewItem);
                    srWrite.WriteLine(sNewItem);
                    srWrite.Write(sTemp);
                }
                else
                {
                    srWrite.Write(sTemp);
                }
  
                srWrite.Close();
                srWrite.Dispose();
                fsTxtWrite.Dispose();
            }
            catch (Exception ex)
            {
                Common.DisplayMsg(this.Text, ex.Message.ToString());
            }
        }

        //  设置下拉框   传入参数(需要设置的下拉框控件，查询的语句，默认第一行的内容)
        public static void SetComboList(DevExpress.XtraEditors.ComboBoxEdit ComboList, ArrayList arrSource = null, DataTable dtSource = null, string FirstRowText = "", bool bSelectFirstItem = false, bool bEditable = false)
        {
            DataTable dtList = null;
            if (dtSource != null)
            {
                dtList = dtSource;
            }
            else if (arrSource != null)
            {
                dtList = new DataTable();
                dtList.Columns.Add("name");
                foreach (string s in arrSource)
                {
                    dtList.Rows.Add(s);
                }
            }
            else { return; }

            int intCount = (dtList != null) ? dtList.Rows.Count : 0;
            if (bEditable)
            {
                ComboList.Properties.TextEditStyle = TextEditStyles.Standard;
            }
            else
            {
                ComboList.Properties.TextEditStyle = TextEditStyles.DisableTextEditor; // 设置 comboBox的文本值不能被编辑
            }
            ComboList.Properties.Items.Clear();
            if (!string.IsNullOrEmpty(FirstRowText)) ComboList.Properties.Items.Add(FirstRowText);

            if (intCount > 0)
            {
                for (int i = 0; i < intCount; i++)
                {
                    ComboList.Properties.Items.Add(dtList.Rows[i][0].ToString());
                }
            }
            if (bSelectFirstItem) ComboList.SelectedIndex = 0; // 设置选中第1项
        }

        public static void DisplayMsg(string sCaption, string sMsg)
        {
            XtraMessageBox.Show(sMsg, sCaption);
        }

希望能帮助到有需要的人。