How to use cookies in ASP.Net applications

In this post we are going to see a step by step example on how to read,write,delete cookies in asp.net websites.

Cookies are small pieces of text that you can associate with a website which are transfered down to the user’s computer when the user visits the website.

You can use any of the versions of Visual studio (VS 2005,VS2008,VS2010 express editions work fine).

I will use VS 2010 Ultimate edition and VB.net as the .Net language of choice.

Before we begin it is very important to note some of the limitations of cookies. They store relatively small amount of information about 4kbytes.

Browsers limit the number of cookies associated with a website ( 20 cookies for a certain website ). There is also a limit on how many cookies a browser can handle regarding all websites and that is about 300.

All the data in cookies is stored as text so bear that in mind that you should not store sensitive information in a cookie. You should use the information in the cookie to identify a user, a user’s last visit e.t.c

1) Create an Asp.net web site and name it as you want.

2) Let’s add a cookie in the cookies collection. In the Page_Load event handling routine of the default.aspx page type

Response.Cookies("LastVisit").Value = DateTime.Now.ToString()
Response.Cookies("LastVisit").Expires = DateTime.Now.AddDays(10)

3)  We add a new cookie now that it will be stored in the user’s computer and we set it to expire after 10 days.So if someone visits our website today and then it visits it after 12 days, the browser will delete the cookie

from the users hard disk.Comment out the two line of code in the Page_Load event handling routine.We can use an alternative way to create a cookie and write information on it.

Dim mycookie As HttpCookie = New HttpCookie("LastVisit")
mycookie.Value = DateTime.Now.ToString()
mycookie.Expires = DateTime.Now.AddDays(10)
Response.Cookies.Add(mycookie)

4)  You can store multiple values in the same cookie with the help of subkeys. Comment out the 4 lines of code above. Type the following lines of code in the Page_Load routine

Response.Cookies("mydata")("LastVisit") = DateTime.Now.ToString()
Response.Cookies("mydata")("username") = "fofo"
Response.Cookies("mydata").Expires = DateTime.Now.AddDays(10)

5) Comment out the line above. We will write the same statement as above with a different syntax.Type the following lines of code in the Page_Load routine

 Dim mycookie As HttpCookie = New HttpCookie("mydata")
mycookie.Values("LastVisit") = DateTime.Now.ToString()
mycookie.Values("username") = "fofo"
mycookie.Expires = DateTime.Now.AddDays(10)
Response.Cookies.Add(mycookie)

6) Another thing we can do with the cookies is to specify the scope of the cookie. For example we might want to have a cookie stored on the user’s computer only

if the user visits a specific folder-page e.g Marketing. So if someone visits http://www.mysite.com the cookie is not visible, but if he visits http://www.mysite.com/marketing and all pages within that folder the cookie is visible.

In order to achieve that we use the Path property to restrict the cookie to a particular path to a website.Comment out the lines above and type the following

Dim mycookie As HttpCookie = New HttpCookie("mydata")

        mycookie.Values("LastVisit") = DateTime.Now.ToString()
        mycookie.Values("username") = "fofo"
        mycookie.Expires = DateTime.Now.AddDays(10)
        mycookie.Path = "/Marketing"
        Response.Cookies.Add(mycookie)

7) Another property we can use is the Domain property. So in the previous example we can comment out the

mycookie.Path = “/Marketing”

and type

mycookie.Domain = "help.mysite.com"

This cookie will only be sent back to the server is the page is associated with the domain “help.mysite.com”

8) In order to read cookies sent through the user’s browser back to the server we do the following.

First you need to add a label web server control to your default.aspx page. Then in the Page_Load event handling routine type

If Not Request.Cookies("LastVisit") Is Nothing Then 

Label1.Text = Server.HtmlEncode(Request.Cookies("LastVisit").Value)
End If

9) Run you application and you will see that you successfully set a cookie and read it back from the user’s computer.

10) If you want to modify the cookie’s value and expiration date you can type something like

Response.Cookies("LastVisit").Value = DateTime.Now.ToString()
Response.Cookies("LastVisit").Expires = DateTime.Now.AddDays(30)

The code above will reset the value of “LastVisit” to the actual current time and set a new expiration date for the cookie

11) If you want to delete a cookie from the user’s computer you can type the following

 Response.Cookies("LastVisit").Expires = DateTime.Now.AddDays(-1)

Then the browser will delete the cookie from the user’s  computer.

If you need the source code just email me.

Hope it helps!!!