How to catch a FtpWebResponse exception in C#

I am building an FTP utility class in C#. In the case that a WebExc开发者_如何学JAVAeption is thrown on a call to FtpWebRequest.GetResponse(), in my case the exception is thrown for the requested file not existing on the remote server the FtpWebResponse variable is out of scope.

But even if I declare the variable outside the try..catch block I get a compile error saying "Use of unassigned local variable 'response'", but as far as I can tell there is no way to assign it until you assign the response via the FtpWebRequest.GetResponse() method.

Can someone please advise, or am I missing something obvious?

Thanks!

Here is my current method:

private void Download(string ftpServer, string ftpPath, string ftpFileName, string localPath, 
                           string localFileName, string ftpUserID, string ftpPassword)
    {
        FtpWebRequest reqFTP;
        FtpWebResponse response;
        try
        {
            reqFTP = (FtpWebRequest)FtpWebRequest.Create(new Uri("ftp://"
               + ftpServer + "/" + ftpPath + "/" + ftpFileName));
            reqFTP.Method = WebRequestMethods.Ftp.DownloadFile;
            reqFTP.UseBinary = true;
            reqFTP.Credentials = new NetworkCredential(ftpUserID,
                                                       ftpPassword);

            /* HERE IS WHERE THE EXCEPTION IS THROWN FOR FILE NOT AVAILABLE*/
            response = (FtpWebResponse)reqFTP.GetResponse();
            Stream ftpStream = response.GetResponseStream();


            FileStream outputStream = new FileStream(localPath + "\\" +
               localFileName, FileMode.Create);

            long cl = response.ContentLength;
            int bufferSize = 2048;
            int readCount;
            byte[] buffer = new byte[bufferSize];

            readCount = ftpStream.Read(buffer, 0, bufferSize);
            while (readCount > 0)
            {
                outputStream.Write(buffer, 0, readCount);
                readCount = ftpStream.Read(buffer, 0, bufferSize);
            }

            ftpStream.Close();
            outputStream.Close();
            response.Close();
        }
        catch (WebException webex)
        {
            /*HERE THE response VARIABLE IS UNASSIGNED*/
            if (response.StatusCode == FtpStatusCode.ActionNotTakenFileUnavailable) { 
                //do something
            }
        }

As generic way to solve this, just assign null to the response first and then check in the catch block if it is null.

    FtpWebResponse response = null;
    try
    {
...
    }
    catch (WebException webex)
    {
        if ((response != null) && (response.StatusCode == FtpStatusCode.ActionNotTakenFileUnavailable)) { 
            //do something
        }
    }

However, in this specific case, you have all the properties you need on the WebException instance (including the server response)!

The correct solution to the problem can be found in this question here:
How to check if file exists on FTP before FtpWebRequest

In short:
Your 'response' variable will always be null because of the error. You need to test the FtpWebResponse from 'webex.Response' (cast it) to get the StatusCode.

Well you could always assign a variable:

FtpWebRequest reqFTP = null;
FtpWebResponse response = null;