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Cookies
A Cookie is a small text file that the browser creates and stores on the hard drive
of your machine. Cookie is just one or more pieces of information stored as text strings.
A Web server sends you a cookie and the browser stores it. The browser then returns
the cookie to the server the next time the page is referenced. The most common use
of a cookie is to store information about the user and preferences the user
makes. For example, assume you like DVD's and register with Ebay to participate
in online auctions. You are required to fill out a form with your name, credit
card details and address. Ebay assigns you an ID, stores your information with
that ID in its database on the server, and sends the ID to your browser as a cookie.
Your browser stores the ID on your hard disk. The next time you go to Ebay, the
ID is sent back to the server. The server looks you up by your ID and customizes the
Web page it sends back to you. The page might say, "Cheap rates on your favorite DVD's".
Creating cookies with ASP.NET is simple and straight forward. The System.Web namespace
offers a class called HttpCookie to create cookies. The
following code demonstrates the creation of cookies. The code assumes that you
have a TextBox, two Buttons and a RadioButtonList control with some items in
it on a Web Forms page. Check the live code demo at the bottom of this page for more.
Private Sub Select_Click(ByVal sender As System.Object, ByVal e As_
System.EventArgs) Handles Select.Click
Dim newCookie As HttpCookie = New HttpCookie("Books")
newCookie.Values.Add("Name", TextBox1.Text)
newCookie.Values.Add("FavBook", RadioButtonList1.SelectedItem.Text)
newCookie.Expires = #12/31/2008#
Response.Cookies.Add(newCookie)
Label3.Text = "Cookie Created"
Select.Visible = False
TextBox1.Visible = False
Label1.Visible = False
Label2.Visible = False
RadioButtonList1.Visible = False
End Sub
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Understanding the Code
 First, we created a variable called newCookie and an
HttpCookie object is instantiated. This object enables us to pass a string when we
create it to identify the name that the browser will use to store the cookie. We called
it Books.
After we created the object, we added information to
it using the Values property and the Add method.
To ensure that the cookie stays on the user's hard drive
for a while we set it's date using the HttpCookie object's Expires property.
To get this cookie sent back to the browser and stored
on the hard drive we used the Response object.
The code listing above creates and stores the cookie on the user's hard drive which
is fine. To retrieve them at a later date, what should be done?
Retriving the cookie
The code below demonstrates how to retrieve a cookie and display information to the
user based on his preferences.
Private Sub Retrieve_Click(ByVal sender As System.Object, ByVal e As_
System.EventArgs) Handles Retrieve.Click
Label3.visible=False
Label4.Text = "Hello" &" "& Request.Cookies("Books")("Name") & "."&_
"We have a new book for you:"
If Request.Cookies("Books")("FavBook") = "VB" Then
Label5.text="XYZ VB Book"
ElseIf Request.Cookies("Books")("FavBook") = "C#" Then
Label5.text="ABC C# Book"
Else
Label5.text="Startvbdotnet.com's ASP Book"
End If
End Sub
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Understanding the Code
First, we used the Request object to retrieve the cookie
and display a message to the user.
Based on the user's selection first time he
accessed the page, we display a new book to him using If..Then..Else conditional.
The path to the location on the hard drive where cookies are stored is
C:\Documents and Settings\Administrator\Cookies.
Live Code Demo
You are required to enter your name, make a selection from the RadioButtonList and
hit the submit button. When you hit the submit button a cookie is created and stored
on your hard drive. When you hit the retrieve button you will be shown a welcome
message and a book will be suggested to you. The cookie that will be created
with the code will be in the form of "administrator@www.startvbdotnet[1].txt" and
it can be found in
C:\Documents and Settings\Administrator\Cookies.
Enter your Name
Select your interest
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