ASP.NET 4 Unleased - p 131 pot

{ BulletedList1.Items.Add“Deleting “ + cookie; Response.Cookies[cookie].Expires = DateTime.Now.AddDays-1; } } Delete All Cookies Delete All Cookies The page in Listing 28.6 l

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<title>Delete Cookie</title>

</head>

<body>

<div>

<asp:Label

id=”lblCookieName”

Text=”Cookie Name:”

AssociatedControlID=”txtCookieName”

Runat=”server” />

<asp:TextBox

id=”txtCookieName”

<asp:Button

id=”btnDelete”

Text=”Delete Cookie”

OnClick=”btnDelete_Click”

</div>

</form>

</body>

</html>

The particular date that you specify when deleting a cookie doesn’t matter as long as it is

in the past In Listing 28.5, the expiration date is set to one day ago

The page in Listing 28.6 deletes all cookies sent from the browser to the current domain

(and path)

LISTING 28.6 DeleteAllCookies.aspx

<%@ Page Language=”C#” %>

<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Transitional//EN”

“http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd”>

void Page_Load()

{

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{

BulletedList1.Items.Add(“Deleting “ + cookie);

Response.Cookies[cookie].Expires = DateTime.Now.AddDays(-1);

}

</script>

<title>Delete All Cookies</title>

</head>

<body>

<div>

<h1>Delete All Cookies</h1>

<asp:BulletedList

id=”BulletedList1”

EnableViewState=”false”

</div>

</form>

</body>

</html>

The page in Listing 28.6 loops through all the cookie names from the Request.Cookies

collection and deletes each cookie

Working with Multivalued Cookies

According to the cookie specifications, browsers should not store more than 20 cookies

from a single domain You can work around this limitation by creating multivalued

cookies

A multivalued cookie is a single cookie that contains subkeys You can create as many

subkeys as you need

For example, the page in Listing 28.7 creates a multivalued cookie named preferences

The preferences cookie stores a first name, last name, and favorite color (see Figure 28.3)

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LISTING 28.7 SetCookieValues.aspx

void btnSubmit_Click(Object s, EventArgs e)

{

Response.Cookies[“preferences”][“firstName”] = txtFirstName.Text;

Response.Cookies[“preferences”][“lastName”] = txtLastName.Text;

Response.Cookies[“preferences”][“favoriteColor”] = txtFavoriteColor.Text;

Response.Cookies[“preferences”].Expires = DateTime.MaxValue;

}

</script>

<title>Set Cookie Values</title>

</head>

FIGURE 28.3 Creating a multivalued cookie

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<asp:Label

id=”lblFirstName”

Text=”First Name:”

AssociatedControlID=”txtFirstName”

<br />

<asp:TextBox

id=”txtFirstName”

<asp:Label

id=”lblLastName”

Text=”Last Name:”

AssociatedControlID=”txtFirstName”

<br />

<asp:TextBox

id=”txtLastName”

<asp:Label

id=”lblFavoriteColor”

Text=”Favorite Color:”

AssociatedControlID=”txtFavoriteColor”

<br />

<asp:TextBox

id=”txtFavoriteColor”

<asp:Button

id=”btnSubmit”

Text=”Submit”

OnClick=”btnSubmit_Click”

</div>

</form>

</body>

</html>

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When you submit the page in Listing 28.7, the following HTTP header is sent to the browser:

Set-Cookie: preferences=firstName=Steve&lastName=Walther&favoriteColor=green;

expires=Fri, 31-Dec-9999 23:59:59 GMT; path=/

The page in Listing 28.8 reads the values from the preferences cookie

LISTING 28.8 GetCookieValues.aspx

void Page_Load()

{

if (Request.Cookies[“preferences”] != null)

{

lblFirstName.Text = Request.Cookies[“preferences”][“firstName”];

lblLastName.Text = Request.Cookies[“preferences”][“lastName”];

lblFavoriteColor.Text = Request.Cookies[“preferences”][“favoriteColor”];

}

</script>

<title>Get Cookie Values</title>

</head>

<body>

<div>

First Name:

<asp:Label

id=”lblFirstName”

<br />

Last Name:

<asp:Label

id=”lblLastName”

<br />

Favorite Color:

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</div>

</form>

</body>

</html>

You can use the HttpCookie.HasKeys property to detect whether a cookie is a normal

cookie or a multivalued cookie

Using Session State

You can’t use a cookie to store a shopping cart A cookie is just too small and too simple

To enable you to work around the limitations of cookies, ASP.NET Framework supports a

feature called Session state

Like cookies, items stored in Session state are scoped to a particular user You can use

Session state to store user preferences or other user-specific data across multiple page

requests

Unlike cookies, Session state has no size limitations If you had a compelling need, you

could store gigabytes of data in Session state Furthermore, unlike cookies, Session state

can represent more complex objects than simple strings of text You can store any object

in Session state For example, you can store a DataSet or a custom shopping cart object in

Session state

You add items to Session state by using the Session object For example, the page in Listing

28.9 adds a new item named message to Session state that has the value Hello World!

LISTING 28.9 SessionSet.aspx

void Page_Load()

{

Session[“message”] = “Hello World!”;

}

</script>

<title>Session Set</title>

</head>

<body>

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<div>

<h1>Session item added!</h1>

</div>

</form>

</body>

</html>

In the Page_Load() event handler in Listing 28.9, a new item is added to the Session

object You can use the Session object just as you would use a Hashtable collection

The page in Listing 28.10 illustrates how you can retrieve the value of an item that you

have stored in Session state

LISTING 28.10 SessionGet.aspx

void Page_Load()

{

lblMessage.Text = Session[“message”].ToString();

}

</script>

<title>Session Get</title>

</head>

<body>

<div>

<asp:Label

id=”lblMessage”

</div>

</form>

</body>

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When you use Session state, a session cookie named ASP.NET_SessionId is added to your

browser automatically This cookie contains a unique identifier It is used to track you as

you move from page to page

When you add items to the Session object, the items are stored on the web server and not

the web browser The ASP.NET_SessionId cookie associates the correct data with the

correct user

By default, if cookies are disabled, Session state does not work You don’t receive an error,

but items that you add to Session state aren’t available when you attempt to retrieve them

in later page requests (You learn how to enable cookieless Session state later in this

section.)

WARNING

Be careful not to abuse Session state by overusing it A separate copy of each item

added to Session state is created for each user who requests the page If you place a

DataSet with 400 records into Session state in a page, and 500 users request the

page, you have 500 copies of that DataSet in memory

By default, ASP.NET Framework assumes that a user has left the website when the user has

not requested a page for more than 20 minutes At that point, any data stored in Session

state for the user is discarded

Storing Database Data in Session State

You can use Session state to create a user-relative cache For example, you can load data

for a user and enable the user to sort or filter the data

The page in Listing 28.11 loads a DataView into Session state The user can sort the

contents of the DataView by using a GridView control (see Figure 28.4)

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LISTING 28.11 SessionDataView.aspx

<%@ Import Namespace=”System.Data” %>

<%@ Import Namespace=”System.Data.SqlClient” %>

<%@ Import Namespace=”System.Web.Configuration” %>

DataView dvMovies;

/// <summary>

/// Load the Movies

/// </summary>

void Page_Load()

{

dvMovies = (DataView)Session[“Movies”];

if (dvMovies == null)

FIGURE 28.4 Sorting a DataView stored in Session state

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new SqlDataAdapter(“SELECT Id,Title,Director FROM Movies”, conString);

DataTable dtblMovies = new DataTable();

dad.Fill(dtblMovies);

dvMovies = new DataView(dtblMovies);

Session[“Movies”] = dvMovies;

}

/// <summary>

/// Sort the Movies

/// </summary>

protected void grdMovies_Sorting(object sender, GridViewSortEventArgs e)

{

dvMovies.Sort = e.SortExpression;

}

/// <summary>

/// Render the Movies

/// </summary>

void Page_PreRender()

{

grdMovies.DataSource = dvMovies;

grdMovies.DataBind();

}

</script>

<title>Session DataView</title>

</head>

<body>

<div>

<asp:GridView

id=”grdMovies”

AllowSorting=”true”

EnableViewState=”false”

OnSorting=”grdMovies_Sorting”

<br />

<asp:LinkButton

id=”lnkReload”

Text=”Reload Page”

</div>

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