FileStream实例重复利用要小心

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;

namespace FileStreamTest
{
    class Program
    {
        static void Main(string[] args)
        {
            String file = @"D:\temp.txt";
            FileStream fileStream;

            if (File.Exists(file))
            {
                fileStream = File.OpenRead(file);
            }
            else
            {
                fileStream = File.Create(file);
            }

            //这里对StreamWriter使用using，会导致在这个域结束之后，对fileStream的流关闭
            using (StreamWriter writer=new StreamWriter(fileStream))
            {
                writer.WriteLine("test some plain text!");
            }

            //这里再传入fileStream的文件流已经被关闭，所以会在运行时报错
            using (StreamReader reader=new StreamReader(fileStream))
            {
                Console.WriteLine(reader.ReadLine());
            }

            fileStream.Close();
            fileStream.Dispose();
        }
    }
}