Why i'm getting exception: ObjectDisposedExcep

问题:

This is the code:

FtpWebResponse response = (FtpWebResponse)reqFTP.GetResponse();
Stream responseStream = response.GetResponseStream();
StreamReader readStream = new StreamReader(responseStream, System.Text.Encoding.UTF8);
long filel = readStream.ReadToEnd().Length;
readStream.Close();
FileStream writeStream = new FileStream(ftpdirectories + "\\" + filenameonly, FileMode.Create);
string fnn = ftpdirectories + "\\" + filenameonly;
int Length = 2048;
Byte[] buffer = new Byte[Length];
int bytesRead = responseStream.Read(buffer, 0, Length);

The exception is on the line:

int bytesRead = responseStream.Read(buffer, 0, Length);

If i'm not using the StreamReader the long and the Close it's working fine but once i'm adding the StreamReader i'm getting the exception.

Cannot access a disposed object.

Object name: 'System.Net.Sockets.NetworkStream'.

 System.ObjectDisposedException was caught
      HResult=-2146232798
      Message=Cannot access a disposed object.
    Object name: 'System.Net.Sockets.NetworkStream'.
      Source=System
      ObjectName=System.Net.Sockets.NetworkStream
      StackTrace:
           at System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 offset, Int32 size)
           at System.Net.FtpDataStream.Read(Byte[] buffer, Int32 offset, Int32 size)
           at FTP_ProgressBar.FtpProgress.DownloadFtpContent(Object sender, String file, String filesdirectories, String fn) in c:\ftp_progressbar\FTP_ProgressBar\FtpProgress.cs:line 284
      InnerException:

Line 284 is:

int bytesRead = responseStream.Read(buffer, 0, Length);

回答1:

ObjectDisposedException: The exception that is thrown when an operation is performed on a disposed object.

when you close readStream

readStream.Close();

StreamReader.Close Method Closes the StreamReader object and the underlying stream, and releases any system resources associated with the reader. This implementation of Close calls the Dispose method passing a true value.

the underlying responseStream which is set in

StreamReader readStream = new StreamReader(responseStream, ...

is closed and closing a stream call dispose method and it get disposed. after that you access responseStream and boom! ObjectDisposedException

回答2:

The Stream gets closed and disposed when the StreamReader gets closed. Check out the MSDN page on the StreamReader Close method for more information.

To wit, the StreamReader's Close method

Closes the StreamReader object and the underlying stream, and releases any system resources associated with the reader.

Along with that:

This implementation of Close calls the Dispose method passing a true value.

回答3:

You using..

StreamReader readStream = new StreamReader(responseStream, System.Text.Encoding.UTF8);

Provide encoding required for response as follows.

StreamReader readStream = new StreamReader(responseStream, System.Text.Encoding.GetEncoding("Windows-1252"));

This happens with German characters like ü, ö, ä etc. So probably UTF-8 fails while reading and closes the stream. Hence, you need to maintain encoding list against URLs or expected response and pass it as above.