[Mono-dev] System.NullReferenceException, what does it mean?

[Chris Toshok]

mono stack trace line numbers are generally 1 off.  So the line which is
throwing the exception is actually:

string responseEncoding = webResponse.ContentEncoding.Trim();

This does in fact work in MS?  what's the value of
webResponse.ContentEncoding?

Chris

On Mon, 2006-04-03 at 12:45 -0600, Wade Maxfield wrote:
> 
>   OH!  Thanks.   Have Done.  The web page returns almost
> *immediately*, no chance of a timeout. 
> 
> The page is at http://ampro2:2001/shm/gdsp.php
> 
>  The contents of the page are as follows:
> 
> CRCErrorCounter: 0:CountOfMessages: 0:CRCCorrectCounter:
> 0:CountOfWords: 0:DownlinkMsgCount: 0:BadMsgCounter: 0:MDBFlag1:
> 0:MDBFlag2: 0:MDBFlag3: 0:HeadVoltage: 0:ToolVoltage: 0:Temp:
> 0:TestMsgCount: 0:TestMsgMissedBlockCnt: 0:BufferOverflowCounter:
> 0:DSPMissedSeqCnt: 0:ResetDSPVariablesFlag: 0:SendTestMsgFlag:
> 0:ToolCurrent: 0:Head: 0:Tail: 0:MissedErrorLogCount: 0:StartTime:
> 0:RunTime: 0: 
> 
> 
>   (We dump a lot of info using monkey, and parse it to show on a
> screen.)
> 
> Here is more information on the crash:
> ----------------------------------------------------------------------------------------------
> maxfield at cfw7245-xp2:~/Desktop/Remote DSP Monitor/RemoteDspMonitor$
> mono --debug bin/Debug/RemoteDspMonitor.exe
> Mono System.Windows.Forms Assembly [Revision: 54007; built: 2005/12/6
> 14:35:24]
> Keyboard: United States keyboard layout (phantom key version)
> Gtk colorscheme read
> Polling:
> http://ampro2:2001/shm/gdsp.php
> 
> Unhandled Exception: System.NullReferenceException: Object reference
> not set to an instance of an object
> in [0x00070] (at /home/maxfield/Desktop/Remote DSP
> Monitor/RemoteDspMonitor/WebPageFetch.cs:51)
> WebPageFetchSpace.GetWebPageClass:GetWebPage ()
> in [0x000cd] WebPageFetchSpace.GetWebPageClass:Run ()
> in (wrapper delegate-invoke) System.MulticastDelegate:invoke_void ()
> ---------------------------------------------------------------------------------------------------
> 
> 
> Here is the relevant code.  line WebPageFetch.cs:51 is indicated below
> with a comment:
> 
> 
> string host = "ampro";
> int  port = 2001;
> string url = "shm/gdsp.php";
> 
> GetWebPage()
>    {
>             UriBuilder uri = new UriBuilder("http",host,port,url);
>             HttpWebRequest webRequest =
>               (HttpWebRequest)WebRequest.Create(uri.ToString());
>             webRequest.Timeout = 1000;
>              if (Debug)
>              {
>             string MyUri = uri.ToString();
>                  Console.WriteLine("Polling: ");
>                  Console.WriteLine(MyUri);
>                  //Console.WriteLine("\n");
>              }
> 
> 
> 
>             HttpWebResponse webResponse =
>               (HttpWebResponse)webRequest.GetResponse();
>             Stream responseStream = webResponse.GetResponseStream();
>             string responseEncoding =
> webResponse.ContentEncoding.Trim();
> 
> /*line 51--> */           if (responseEncoding.Length == 0)
>               responseEncoding="us-ascii";
> 
>             StreamReader responseReader = new
> StreamReader(responseStream,
>               System.Text.Encoding.GetEncoding(responseEncoding));
>             return(responseReader.ReadToEnd());
> }
> 
> 
> 
> On 4/3/06, Michael Hutchinson <m.j.hutchinson at gmail.com> wrote:
>         >  Unhandled Exception: System.NullReferenceException: Object
>         reference not
>         > set to an instance of an object
>         >  in <0x001c6> WebPageFetchSpace.GetWebPageClass:GetWebPage
>         > ()
>         >  in <0x0007b> WebPageFetchSpace.GetWebPageClass:Run ()
>         
>         There's not much anyone can do with that trace, especially as
>         we don't
>         have the source. If you compile with debug symbols (mcs
>         -debug) and
>         run with debugging support (mono --debug) you'll get line
>         numbers, and 
>         will be able to find out what operation is causing that
>         exception.
>         
>         
>         Michael
> 
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