c# IO操作（带进度的文件复制器，读取文本文件的指定行）

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();

public override long Seek (
long offset,
SeekOrigin origin
)

Code

 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;
            }
        }
    }