Asp.net implements attachment download (garbled)

Code

    Private     Void  Page_load (  Object  Sender, system. eventargs E)
{
  If  (Request. querystring [  "  Recordid  " ]  ! =     Null     &&  Request. querystring [  "  Recordid  "  ]. Tostring ()  ! =     ""  )
{
Startech. dbutility. adohelper  = Startech. dbutility. adohelper. createhelper (  "  News_instance  "  );
System. Data. datatable resourceds  =  Adohelper. executesqldataset (  "  Select * From t_news_resource where recordid ='  "     +  Request. querystring [  "  Recordid "  ]. Tostring ()  +     "  '  "  ). Tables [  0  ];
  If  (Resourceds. Rows. Count  >     0  )
{
  String Filepath  =     This  . Mappath (resourceds. Rows [  0  ] [  "  Path  "  ]. Tostring ());
  Byte  [] Bytefile  =  Getfilebyte (filepath );
  If  (Bytefile ! =     Null  )
{
  String  Filetype  =  System. Io. Path. getextension (filepath );
  String  Filename  =  System. Io. Path. getfilename (filepath );
Response. Clear ();
Response. headerencoding  = System. Text. encoding. default;
Response. addheader (  "  Content-Disposition  "  ,  "  Attachment; filename =  "     +  Filename );
Response. addheader (  "  Content-Length  " , Bytefile. length. tostring ());
Response. contenttype  =  Checktype (filetype );
Response. binarywrite (bytefile );
Response. End ();
}
  Else  
{
Response. Write (  "  <Font color = Red> no attachment is found! [<A href = 'javascript: window. Opener = NULL; window. Close () '> close </a>] </font>  "  );
}
}
}
  Else 
{
Response. Write (  "  <Font color = Red> parameter error or insufficient permissions [<a href = 'javascript: window. Close () '> close </a>] </font>  "  );
}
}
  //  Obtain the binary stream of a file  
    Private  Byte [] getfilebyte (  String  Path)
{
  Try 
{
System. Io. filestream File  =     New  System. Io. filestream (path, system. Io. filemode. Open, system. Io. fileaccess. Read );
Byte [] imgbyte  =     New  Byte;
File. Read (imgbyte,  0  , Imgbyte. Length );
File. Close ();
  Return  Imgbyte;
}
 Catch  (Exception ex)
{
  String  Str  =  Ex. message;
  Return     Null  ;
}
}
  ///     <Summary>  
  ///  Obtains the corresponding "http mime" type of the output stream based on the file extension.
 ///     </Summary>  
  ///     <Param name = "filetype"> </param>  
  ///     <Returns> </returns>  
    Private     String Checktype (  String  Filetype)
{
  String  Contenttype;
  Switch  (Filetype. tolower ())
{
  Case     "  . ASF  "  :
Contenttype  =     " Video/X-MS-ASF  "  ;
  Break  ;
  Case     "  . Avi  "  :
Contenttype  =     "  Video/Avi  "  ;
 Break  ;
  Case     "  . Doc  "  :
Contenttype  =     "  Application/MSWord  "  ;  Break  ;
  Case    "  . Zip  "  :
Contenttype  =     "  Application/zip  "  ;  Break  ;
  Case     "  . Xls "  :
Contenttype  =     "  Application/vnd. MS-Excel  "  ;  Break  ;
  Case     "  . Gif  "  :
Contenttype  =    "  Image/GIF  "  ;  Break  ;
  Case     "  . Jpg  "  :
Contenttype  =     "  Image/JPEG "  ;  Break  ;
  Case     "  JPEG  "  :
Contenttype  =     "  Image/JPEG  "  ;  Break ;
  Case     "  . Wav  "  :
Contenttype  =     "  Audio/WAV  "  ;  Break  ;
  Case    "  . MP3  "  :
Contenttype  =     "  Audio/mpeg3  "  ;  Break  ;
  Case     "  . Mpg  " :
Contenttype  =     "  Video/MPEG  "  ;  Break  ;
  Case     "  . Mepg  "  :
Contenttype  =    "  Video/MPEG  "  ;  Break  ;
  Case     "  . Rtf  "  :
Contenttype  =     "  Application/RTF  " ;  Break  ;
  Case     "  . Html  "  :
Contenttype  =     "  Text/html  "  ;  Break  ;
 Case     "  . Htm  "  :
Contenttype  =     "  Text/html  "  ;  Break  ;
  Case     " . Txt  "  :
Contenttype  =     "  Text/plain  "  ;  Break  ;
  Default  :
Contenttype  =     " Application/octet-stream  "  ;
  Break  ;
}
  Return  Contenttype;
}