//把txt清空

            FileStream stream = File.Open(Adr,FileMode.OpenOrCreate,FileAccess.Write);

            stream.Seek(0, SeekOrigin.Begin);

            stream.SetLength(0);

            stream.Close();

            //向txt里面追加信息

            StreamWriter sw = new StreamWriter(Adr,true,Encoding.GetEncoding("gb2312"));

            sw.WriteLine(str);

            sw.Flush();

            sw.Close();