/// <summary>

        /// 将DataTable里面的内容写入txt文件

        /// </summary>

        /// <param name="dt">数据表</param>

        /// <param name="columnNames">要写的字段列表</param>

        /// <param name="fileName">文件名，全路径，建议以.txt为后缀</param>

        /// <param name="encoding">文件编码格式</param>

        /// <param name="fieldsTerminated">字段分隔符，默认为\t制表符</param>

        /// <returns></returns>

        public void WriteDataTableIntoFile(DataTable dt, List<string> columnNames, string fileName, Encoding encoding, string fieldsTerminated = "\t")

        {

            if (dt == null)

            {

                return;

            }

            //写数据文件

            using (StreamWriter streamWriter = new StreamWriter(fileName, false, encoding))

            {

                int col = ;

                foreach (DataRow dr in dt.Rows)

                {

                    col = ;

                    foreach (string column in columnNames)

                    {

                        if (col > )

                        {

                            streamWriter.Write(fieldsTerminated);

                        }

                        if (dt.Columns[column].DataType == typeof(DateTime))

                        {

                            if (dr[column] == DBNull.Value)

                            {

                                //streamWriter.Write("0000-00-00 00:00:00");

                            }

                            else

                            {

                                streamWriter.Write(((DateTime)dr[column]).ToString("yyyy-MM-dd HH:mm:ss"));

                            }

                        }

                        else

                        {

                            streamWriter.Write(Convert.ToString(dr[column]).Replace('\t', ' ').Replace('\r', ' ').Replace('\n', ' '));

                        }

                        col++;

                    }

                    streamWriter.WriteLine();

                    streamWriter.Flush();

                }

                streamWriter.Close();

                streamWriter.Dispose();

            }

        }