//Stream to File

MemoryStream ms=...Stream;

ms.Position = ;

byte[] buffer = new byte[ms.Length];

ms.Read(buffer, , (int)ms.Length);

File.WriteAllBytes(filepath, buffer);//写入文件

// StreamRead,StreamWrite,File只能操作文本文件 
//FileStream可以操作所有格式 包括文本，文件，图片，视频

//SreamRead读取文件

using (StreamReader reader = new StreamReader(filepath))

 {

        //reader.ReadLine();读取第一行

        string data = reader.ReadToEnd();//读取所有

 }

//StreamWrite写入文件

 using (StreamWriter writer = new StreamWriter(filepath))

 {

         //writer.Write("写入的内容");

         //也可以如下面一行一行写入

         writer.WriteLine("");

         writer.WriteLine("");

         writer.WriteLine(picName);

         writer.WriteLine(txtCount.Text);

 }  

//File即可以读取文本 也可以写入文本

//读取

string data = File.ReadAllText(filepath);

string[] datas = File.ReadAllLines(filepath);

//写入

string[] ss = new string[] {"arr1","arr2" };

File.WriteAllLines(filepath, ss);

File.WriteAllText(filepath, "\r\n换行\r\n"); 
//附加
File.AppendAllLines(filepath,ss);
File.AppendAllText(filepath,str); 

//FileStream可以操作所有格式 包括文本，文件，图片，视频

//FileStream读取

string ss = null;

byte[] buffer = new byte[ *  * ];  //针对大文件1M1M的读取

 using (FileStream sr = new FileStream(sfilepath, FileMode.OpenOrCreate, FileAccess.Read))

 {

    int sss = sr.Read(buffer, , buffer.Length);

    ss = Encoding.Default.GetString(buffer, , sss);

 }

//FileStream写入

using (FileStream fsWrite = new FileStream(filepath, FileMode.OpenOrCreate, FileAccess.Write))

{

    byte[] buffer = Encoding.Default.GetBytes(str);

    fsWrite.Write(buffer, , buffer.Length);

}

/// <summary>

/// 将 Stream 写入文件

/// </summary>

public void StreamToFile(Stream stream,string filepath)

{

    // 把 Stream 转换成 byte[]

    byte[] bytes = new byte[stream.Length];

    stream.Read(bytes, , bytes.Length);

    // 设置当前流的位置为流的开始

    stream.Seek(, SeekOrigin.Begin);

    // 把 byte[] 写入文件

    FileStream fs = new FileStream(filepath, FileMode.Create);

    BinaryWriter bw = new BinaryWriter(fs);

    bw.Write(bytes);

    bw.Close();

    fs.Close();

}

/// <summary>

/// 从文件读取 Stream

/// </summary>

public Stream FileToStream(string filepath)

{

    // 打开文件

    FileStream fileStream = new FileStream(filepath, FileMode.Open, FileAccess.Read, FileShare.Read);

    // 读取文件的 byte[]

    byte[] bytes = new byte[fileStream.Length];

    fileStream.Read(bytes, , bytes.Length);

    fileStream.Close();

    // 把 byte[] 转换成 Stream

    Stream stream = new MemoryStream(bytes);

    return stream;

}  

public static void CopyFile(string soucre, string target)

        {

            //读取的流

            using (FileStream fsRead = new FileStream(soucre, FileMode.Open, FileAccess.Read))

            {

                //写入的流

                using (FileStream fsWrite = new FileStream(target, FileMode.OpenOrCreate, FileAccess.Write))

                {

                    byte[] buffer = new byte[ *  * ];

                    while (true)

                    {

                        int r = fsRead.Read(buffer, , buffer.Length);

                        //0代表已经读取完

                        if (r == )

                        {

                            break;

                        }

                        fsWrite.Write(buffer, , r);

                    }

                }

            }

        }