Object reference not set to an instance when modifying an existing cookie in code behind

Question

In the line "Response.Cookies...", I get an object reference not set to an instance of an object. Is there a way to fix this and use a timer in my ASPX code behind?

protected void Page_Load(object sender, EventArgs e)
{

    object o = new object();

    TimerCallback timercallback = new TimerCallback(StartCallback);

    System.Threading.Timer timer = new Timer(timercallback, o, 0, 50000);



    if (are.WaitOne())
    {
        Response.Redirect("Default.aspx");
    }
}


public void StartCallback(object o)
{
    //Request.Cookies["haspassed?"].Value = "";

    Response.Cookies["haspassed?"].Expires = System.DateTime.Now.AddMonths(-1);

    are.Set();
}

Thanks

Answer 1

iirc the new thread which StartCallback is going to operate in isn't going to have an HTTPContext, so the nullpointer is that Response does not exist. Why not pass it the context as "o"?

Answer 2

So I cast o to a HttpContext object? I'll give that a go.

I'm using a C# timer out of preference of server side coding than JS, really.

Answer 3

It's an odd problem; Response (according to Reflector) is:

[Browsable(false), DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]
public HttpResponse Response
{
    get
    {
        if (this._response == null)
        {
            throw new HttpException(SR.GetString("Response_not_available"));
        }
        return this._response;
    }
}

So it can't return null - you'd get an HttpException instead.

Likewise, Cookies is:

public HttpCookieCollection Cookies
{
    get
    {
        if (this._cookies == null)
        {
            this._cookies = new HttpCookieCollection(this, false);
        }
        return this._cookies;
    }
}

So you wouldn't get null there either.

The Cookies' indexer? Nope:

public HttpCookie Get(string name)
{
    HttpCookie cookie = (HttpCookie) base.BaseGet(name);
    if ((cookie == null) && (this._response != null))
    {
        cookie = new HttpCookie(name);
        this.AddCookie(cookie, true);
        this._response.OnCookieAdd(cookie);
    }
    return cookie;
}

So I thought, the only thing we have left, is inside the Cookies indexer, if this._response == null, the cookie setting will not happen and this will return null. But that can't happen either since _cookies is only ever in that line we saw earlier, which calls a constructor which is the only place where _response is set - set to the correct HttpRespones, never null.

In conclusion, I've dug deep in there and can't see any way for the Response.Cookies["haspassed?"].Expires setter to ever throw a NullReferenceException.