c# IO操作（带进度的文件复制器，读取文本文件的指定行）

 

带进度的文件复制器

     基本原理就是通过Stream的BeginRead来异步复制文件，同时刷新进度条的状态

 

 

 代码

读取文件的指定行

1、通过StreamReader的Readline

            StreamReader sr = new StreamReader("E:\\abc.txt");
            Console.WriteLine("Peek读取");
            var i = 0;
            while (sr.Peek() >= 0)
            {
                if (++i == 50000000-1)
                {
                    Console.WriteLine(sr.ReadLine());
                    break;
                }
                continue;
            }
            sr.Close();

2、通过 FileStream.seek()来读取

Seek（）方法的定义如下

public override long Seek (
long offset,
SeekOrigin origin
)

只要知道offset就可以了！

于是我们可以定义一个类，将每行开始的offset找出来，有了每行开始的offset，读取就自然不成问题了

 public class ReadByLine

    {

        public ReadByLine(string name)

        {

            PositionMap=new List<long>();

            FileName = name;

            Done = false;

        }

        public bool Done

        {

            get;

            set;

        }



        /**//// <summary>

        /// 当前流位置

        /// </summary>

        public long Position { get; set; }



        /**//// <summary>

        /// 文件的行数

        /// </summary>

        public long Lines { get; set; }



        /**//// <summary>

        /// 文件名(包含路径)

        /// </summary>

        public string FileName { get; set; }



        /**//// <summary>

        ///  行位置列表

        /// </summary>

        public List<long> PositionMap { get; set; }



        private StreamReader sr;

        private FileStream fs;



        /**//// <summary>

        /// 打开文件

        /// </summary>

        /// <returns></returns>

        public bool Open()

        {

            try

            {

                //初始化各流

                sr = new StreamReader(FileName);

                InitMap();

                return true;

            }

            catch (Exception e)

            {

                return false;

            }

        }



        private void InitMap()

        {

      

            Lines = 1;

            Position = 0;

            //在地图中加入首条数据的位置信息

            PositionMap.Add(Position);



            //顺序建立文件地图

            while (sr.Peek()>0)

            {

                var str = sr.ReadLine();

                Position +=Encoding.UTF8.GetBytes(str).Length+ 2;

                PositionMap.Add(Position);

                Lines++;

            }

            Done = true;

            sr.Close();

        }



        public string ReadLine(int line)

        {

            bool flag = true;

            var str="";

            while (flag)

            {

                if (!Done) continue;

                fs = new FileStream(FileName, FileMode.Open);

                fs.Seek(PositionMap[line], SeekOrigin.Begin);

                var reader = new StreamReader(fs);

                str = reader.ReadLine();

                reader.Close();

                fs.Close();

                flag = false;

            }

            return str;

        }



        public bool Close()

        {

            try

            {

                //fs.Close();

                sr.Close();

                return true;

            }

            catch

            {

                return false;

            }

        }

    }