Create Cookie ASP.NET & MVC

Question

I have a quite simple problem. I want to create a cookie at a Client, that is created by the server. I've found a lot of pages that describe, how to use it - but I always stuck at the same point.

I have a DBController that gets invoked when there is a request to the DB.

The DBController's constructor is like this:

public class DBController : Controller
{
    public DBController()
    {
        HttpCookie StudentCookies = new HttpCookie("StudentCookies");
        StudentCookies.Value = "hallo";
        StudentCookies.Expires = DateTime.Now.AddHours(1);
        Response.Cookies.Add(StudentCookies);
        Response.Flush();
    }

    [... more code ...]

}

I get the Error "Object reference not set to an instance of an object" at:

StudentCookies.Expire = DateTime.Now.AddHours(1);

This is a kind of a basic error message. So what kind of basic thing I've forgot?

I suspect that Response is null in the controller constructor. It get's set later on. Try your code in an action method. — Jim
– Jim, Commented Sep 8, 2016 at 11:58

lr123 · Accepted Answer · 2018-08-31 09:33:32Z

46

The problem is you cannot add to the response in constructor of the controller. The Response object has not been created, so it is getting a null reference, try adding a method for adding the cookie and calling it in the action method. Like so:

private HttpCookie CreateStudentCookie()
{
    HttpCookie StudentCookies = new HttpCookie("StudentCookies");
    StudentCookies.Value = "hallo";
    StudentCookies.Expires = DateTime.Now.AddHours(1);
    return StudentCookies;
}

//some action method
Response.Cookies.Add(CreateStudentCookie());

edited Aug 31, 2018 at 9:33

lr123

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answered Sep 8, 2016 at 12:07

James Ralston

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Comments

James Skemp · Accepted Answer · 2019-11-21 18:04:11Z

15

Use Response.SetCookie(), because Response.Cookie.Add() can add multiple cookies, whereas SetCookie() will update an existing cookie. So I think your problem can be solved.

public DBController()
{
    HttpCookie StudentCookies = new HttpCookie("StudentCookies");
    StudentCookies.Value = "hallo";
    StudentCookies.Expires = DateTime.Now.AddHours(1);
    Response.SetCookie(StudentCookies);
    Response.Flush();
}

edited Nov 21, 2019 at 18:04

James Skemp

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answered Sep 8, 2016 at 12:02

Shekhar Patel

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2 Comments

Hina Khuman Over a year ago

Using your method too 'System.NullReferenceException' occurs at line Response.SetCookie(StudentCookies);

yesfabime Over a year ago

In reference to Jim's comment, your provided code doesn't work

Bruno De Freitas Barros · Accepted Answer · 2020-08-18 15:23:03Z

2

Use

Response.Cookies["StudentCookies"].Value = "hallo";

to update existing cookie.

answered Aug 18, 2020 at 15:23

Bruno De Freitas Barros

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1 Comment

Jck Over a year ago

It looks like in .Net core is now: Response.Cookies.Append("StudentCookies", "hallo");

Radu · Accepted Answer · 2017-03-31 08:46:59Z

1

You could use the Initialize() method of the controller instead of the constructor. In the initialize function the Request object is available. I suspect that the same action can be taken with the Responseobject.

edited Mar 31, 2017 at 8:46

answered Sep 8, 2016 at 12:35

Radu

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