How to process WebResponse when .NET throws WebException ((400) Bad Request)?

I'm using Facebook Graph Api and trying to ge开发者_Python百科t user data. I'm sending user access token and in case this token is expired or invalid Facebook returns status code 400 and this response:

{
    "error": {
        "message": "Error validating access token: The session is invalid because the user logged out.",
        "type": "OAuthException"
    }
}

The problem is that when I use this C# code:

try {
   webResponse = webRequest.GetResponse(); // in case of status code 400 .NET throws WebException here
} catch (WebException ex) {
}

If status code is 400 .NET throws WebException and my webResponse is null after exception is caught so I have no chance to process it. I want to do it to make sure that the problem is in expired token and not somewhere else.

Is there a way to do it?

Thanks.

Using a try/catch block like this and processing the error message appropriately should work fine:

    var request = (HttpWebRequest)WebRequest.Create(address);
    try {
        using (var response = request.GetResponse() as HttpWebResponse) {
            if (request.HaveResponse && response != null) {
                using (var reader = new StreamReader(response.GetResponseStream())) {
                    string result = reader.ReadToEnd();
                }
            }
        }
    }
    catch (WebException wex) {
        if (wex.Response != null) {
            using (var errorResponse = (HttpWebResponse)wex.Response) {
                using (var reader = new StreamReader(errorResponse.GetResponseStream())) {
                    string error = reader.ReadToEnd();
                    //TODO: use JSON.net to parse this string and look at the error message
                }
            }
        }
    }
}

However, using the Facebook C# SDK makes this all really easy so that you don't have to process this yourself.

The WebException still has the "real" response in the Response property (assuming there was a response at all) so you can get the data from that within the catch block.