通过对象传递networkcredentails时的对象引用错误 [英] object reference error while passing networkcredentails through object

问题描述

hi
i我正在使用FTP下载文件。

所以即时使用FtpWebRequest类。

当我通过网络凭证硬编码时，我没有收到任何错误。

但是当我使用NetworkCredential对象传递凭证时，我得到一个错误'对象引用没有设置为对象的实例'。

以下是您的评论代码：

 ' 这种方式不会产生错误 
  Dim  lo  As  新 clsFTPDownload（新 NetworkCredential（  userid，  userpwd），FTP_Path）
 
 '  dim ftpcred as new NetworkCredential  
 '  ftpcred.UserName =userid 
 '  ftpcred.Password =userpwd 
 ' < span class =code-comment> dim lo As new clsFTPDownload（ftpcred，FTP_Path）'产生错误 
 
  Dim  imgdata 作为 字节（）= lo.Download 
 
 
 公开  class  clsFTPDownload 
 
  private  _ftpcredentails  as   new  NetworkCredential 
  private  _ftppath  as  uri 
  private  _IsKeepAlive  as   boolean  
 
  sub   new （ byval  ftpcred  as  NetworkCredential， byval  fpath  as  uri）
 _IsKeepAlive = false 
 _ftpcredentails = ftpcred 
 _ftppath = fpath 
  end   sub  
 
 公共 功能下载（） 作为 字节（）
  Dim  reqFTP 作为 FtpWebRequest 
 尝试 
 如果 _ftppath.ToString.Trim = 字符串 .Empty 那么 
 抛出 新异常（ 空白FTP路径）
 结束 如果 
 
 reqFTP =  CType （FtpWebRequest.Create（_ftppath），FtpWebRequest）
 reqFTP.Method = WebRequestMethods.Ftp.DownloadFile 
 reqFTP.Credentials = _ftpcredentails 
 reqFTP.KeepAlive = _IsKeepAlive 
 reqFTP.UseBinary =  True  
 reqFTP.Proxy = 没什么 
 reqFTP.UsePassive = 错误 
 
 昏暗 response  As  WebResponse =  CType （reqFTP.GetResponse，FtpWebResponse）' 此处遇到对象引用错误 
  Dim  responseStream  As  Stream = response.GetResponseStream 
 
  Dim  mem  as  新 MemoryStream 
 
 responseStream.CopyTo（mem）
 
  Dim  bytes  As   Byte （）= mem.GetBuffer 
 mem.Close（）
 response.Close（）
 
 返回字节
 
 
  Catch  wEx  As  WebException 
  throw  
  Catch  ex  As  Exceptio n 
 投掷 
 最后 
 reqFTP.Abort（）
 结束 尝试 
 结束 功能 
  end   class  

解决方案

http://mattmitchell.com.au/zebras-in-system-net-networkcredential/





参考上面的链接：

  dim  ftpcred  as   new  NetworkCredential 
 ftpcred。 UserName =   userid 
 ftpcred.Password =   userpwd 
 ftpcred.domain =   ' 明确添加 
  dim  lo 作为 新 clsFTPDownload（ftpcred，FTP_Path）' 现在不会产生错误 

hi i am using FTP for downloading a file.
so i m using FtpWebRequest class for the same.
when i m passing the network credentials hardcoded, i don't receive any error.
but when i m using a NetworkCredential object to pass the credentails , i get an error 'object reference not set to an instance of object'.
Below is the code for your review:

'this way doesn't produce error
Dim lo As New clsFTPDownload(New NetworkCredential("userid", "userpwd"), FTP_Path)

'dim ftpcred as new NetworkCredential
'ftpcred.UserName="userid"
'ftpcred.Password="userpwd"
'dim lo As New clsFTPDownload(ftpcred, FTP_Path) 'produces error

Dim imgdata As Byte() = lo.Download


Public class clsFTPDownload

private _ftpcredentails as new NetworkCredential
private _ftppath as uri
private _IsKeepAlive as boolean

sub new(byval ftpcred as NetworkCredential, byval fpath as uri)
    _IsKeepAlive=false
    _ftpcredentails =ftpcred 
    _ftppath =fpath 
end sub

Public Function Download() As Byte()
        Dim reqFTP As FtpWebRequest
        Try
            If _ftppath.ToString.Trim = String.Empty Then
                Throw New Exception("blank FTP path")
            End If

            reqFTP = CType(FtpWebRequest.Create(_ftppath), FtpWebRequest)
            reqFTP.Method = WebRequestMethods.Ftp.DownloadFile
            reqFTP.Credentials = _ftpcredentails
            reqFTP.KeepAlive = _IsKeepAlive
            reqFTP.UseBinary = True
            reqFTP.Proxy = Nothing
            reqFTP.UsePassive = False

            Dim response As WebResponse = CType(reqFTP.GetResponse, FtpWebResponse) 'here object reference error is encountered
            Dim responseStream As Stream = response.GetResponseStream

            Dim mem As New MemoryStream

            responseStream.CopyTo(mem)

            Dim bytes As Byte() = mem.GetBuffer
            mem.Close()
            response.Close()

            Return bytes

      
        Catch wEx As WebException
            throw          
        Catch ex As Exception
            Throw 
        Finally
            reqFTP.Abort()
        End Try
    End Function
end class

解决方案

http://mattmitchell.com.au/zebras-in-system-net-networkcredential/


referring to above link:

dim ftpcred as new NetworkCredential
ftpcred.UserName="userid"
ftpcred.Password="userpwd"
ftpcred.domain="" 'added explicitly
dim lo As New clsFTPDownload(ftpcred, FTP_Path) 'won't produce error now

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