最简单的:

--------写

 //content是要写入文本的字符串

 //(@txtPath + @"\" + rid + ".txt");要被写入的TXT

  StreamWriter sw = new StreamWriter(@txtPath + @"\" + rid + ".txt");

  sw.WriteLine(content);

  sw.Close();

 ---------读

 //folder被读取的文件路径

 text = File.ReadAllText(folder, System.Text.Encoding.GetEncoding("gb2312"));

-------写入流

             //将string写入文件

             try

                 {

                     FileStream fs = new FileStream(@"d:\数据处理\法规20080116HTML\" + Actid.ToString() + ".html", FileMode.OpenOrCreate, FileAccess.Write);

                     StreamWriter sw = new StreamWriter(fs,System.Text.Encoding.GetEncoding("gb2312"));

                     sw.Flush();

                     sw.BaseStream.Seek(0, SeekOrigin.Begin);

                     sw.Write(pageContent);

                     sw.Close();

                 }

                 catch (Exception ex) { }

 //HTTP向应后写出文件

HttpWebRequest myWebRequest = (HttpWebRequest)WebRequest.Create("http://www.microsoft.com");

 WebResponse result = null;

 try

 {

     myWebRequest = (HttpWebRequest)WebRequest.Create(Url);

     result = myWebRequest.GetResponse();

     Stream response = result.GetResponseStream();

     byte[] bytes = new byte[10240];

     int n = 1;

    FileStream fs = File.Create(@"d:\数据处理\法规20080116HTML\" + Actid.ToString() + ".html");

     while (n > 0)

     {

         n = response.Read(bytes, 0, 10240);

         fs.Write(bytes, 0, n);

     }

     response.Close();

     fs.Close();

 }

 catch (Exception ex) { }

//读取

string FileContent = File.ReadAllText(path, System.Text.Encoding.GetEncoding("gb2312"));