C# And Cookies

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Cookies allow you to store small bitsof data on the user’s computer. They take up a small amount of space onthe user’s hard drive and are often useful for storing nonessentialinformation, such as user preferences.

TIP

Store information that you are willing tolose in cookies. Users can delete cookies at any time, and some usersdisable them altogether.

ASP.NET lets you manipulate cookies quite easily with the Cookies collection on the Request and Response objects. Listings 3.2 and 3.3 are two companion pages that will read and write cookies that you enter. Figures 3.3 and 3.4 show the two pages.

Fig 3.3

Fig 3.4

Listing 3.2 WriteCookies.aspx: Writing Arbitrary Cookies

1: <%@ language=”C#” %>
2: <script runat=”server”>
3: void WriteClicked(Object Sender, EventArgs e)
4: {
5: //Create a new cookie, passing the name into the constructor
6: HttpCookie cookie = new HttpCookie(NameField.Text);
7:
8: //Set the cookies value
9: cookie.Value = ValueField.Text;
10:
11: //Set the cookie to expire in 1 minute
12: DateTime dtNow = DateTime.Now;
13: TimeSpan tsMinute = new TimeSpan(0, 0, 1, 0);
14: cookie.Expires = dtNow + tsMinute;
15:
16: //Add the cookie
17: Response.Cookies.Add(cookie);
18:
19: Response.Write(“Cookie written. <br><hr>”);
20: }
21: </script>
22: <html>
23: <body>
24: <h3>Use the button below to write cookies to your browser </h3>
25: The cookies will expire in one minute.
26: <form runat=”server”>
27: Cookie Name <asp:textbox id=”NameField” runat=”server”/><br>
28: Cookie Value <asp:textbox id=”ValueField” runat=”server”/><br>
29: <asp:button text=”WriteCookie” onclick=”WriteClicked” runat=”server” /><br>
30: </form>
31: <a href=”readcookies.aspx”>Read the cookies</a>
32: </body>
33: </html>

Listing 3.3 ReadCoookies.aspx: Reading Cookies Written from the `WriteCookies` Example

1: <%@ language=”C#” %>
2: <script runat=”server”>
3: void ReadClicked(Object Sender, EventArgs e)
4: {
5: //Get the cookie name the user entered
6: String strCookieName = NameField.Text;
7:
8: //Grab the cookie
9: HttpCookie cookie = Request.Cookies[strCookieName];
10:
11: //Check to make sure the cookie exists
12: if (null == cookie) {
13: Response.Write(“Cookie not found. <br><hr>”);
14: }
15: else {
16: //Write the cookie value
17: String strCookieValue = cookie.Value.ToString();
18: Response.Write(“The ” + strCookieName + ” cookie contains: <b>”
19: + strCookieValue + “</b><br><hr>”);
20: }
21: }
22: </script>
23: <html>
24: <body>
25: Use the button below to read a cookie<br>
26: <form runat=”server”>
27: Cookie Name <asp:textbox id=”NameField” runat=”server” />
28: <asp:button text=”ReadCookie” onclick=”ReadClicked” runat=”server” />
29: </form>
30: <a href=”writecookies.aspx”>Write Cookies</a>
31: </body>
32: </html>