Transcript Response.Cookies("cookie")("key") = "value"

CIS 451: Cookies
Dr. Ralph D. Westfall
February, 2009
Problem
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server mostly tracks requests for files
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memory doesn't know who is asking for files
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very efficient for high volume of users
even if from link on file in same web site
to help server, could send identification
identification needs to associated with all files
requested by same user of application
use HTML "hidden fields" in later pages?
<INPUT TYPE="hidden" NAME="[ ]" VALUE="[ ]">
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Possible Solutions
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password login (+ hidden fields)
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advantage: highest security
disadvantage: extra work for customer
automated identification (+ hidden)
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could generate a random # to ID customer
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advantage: no extra work for customer
disadvantage: only good for one session
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can' track repeat visits by same person
Another Solution: Cookies
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information stored in file on client computer
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advantages
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National Semiconductor cookies policy
user only needs to enter data one time
data "persists," so it is available in later
sessions
disadvantages
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some users won't allow cookies (very few?)
cookies can be removed from user's
computer
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expire, replaced by newer ones, or cleared by user
Cookies
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cookies have names
a cookie can have multiple values
cookie data accessed by the cookie's name
(and by the keys if more than one value)
cookies are part of both the Request and
Response ASP intrinsic objects
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created by Response.Cookies methods
stored in Request.Cookies "collection"
Working with Cookies
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creating
Response.Cookies("cookie")("key") = "value"
'substitute "literals" or string variables for
'items within " "
'note similarities to selection of multiple
'items in a ListBox on HTML or .NET form
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deleting
Response.Cache.SetExpires _ 'line continuation
(DateTime.Now.AddDays(-5))'positive or negative
'negative value deletes on client
'but session still has data
Using QueryString in an aspx File
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can create the same effect sending
from an aspx file as from a html file
Response.Redirect("rsp.aspx?Name=" & _
this.txtName.Text & "&LastName=" & _
this.txtLastName.Text)
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values are URL encoded and visible in
browser address of destination page
one way to migrate from html to aspx
Working with Cookies - 2
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accessing
strValue =
Request.Cookies("cookie")("key")
'note that data is accessed from
Request object
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counting cookies
intCount = Request.Cookies.Count + 1
'0 based: need to add 1 to get actual #
Viewing Cookies
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install Web Developer add-on for
Firefox
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Cookies>View Cookie Information
Cookie Exercise
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create a web project in VB.NET
add one TextBox and a Button to the
Default.aspx form
add another form named
CookieRead.aspx and add a Label to it
Cookie Exercise - 2
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double-click on each form to create the
aspx.vb code-behind files
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or right-click on the file names in Solution
Explorer>View Code
download cookiewrite.aspx and
cookieread.aspx from Code Samples
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use the code examples to get the two
pages to run
Cookie Exercise - 3
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make enhancements
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add some more input fields to Default.aspx
and modify CookieRead.aspx to output
these new fields
add a Button to reset TextBoxes to blanks
rather than reloading cookie values
add Button to 2nd page to delete cookie