Cookies
Cookies are small pieces of text, stored on the client's computer to be used only by the website setting the cookies. This allows webapplications to save information for the user, and then re-use it on each page if needed. Here is an example where we save a users choice of background color:
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" > <head runat="server"> <title>Cookies</title> </head> <body runat="server" id="BodyTag"> <form id="form1" runat="server"> <asp:DropDownList runat="server" id="ColorSelector" autopostback="true" onselectedindexchanged="ColorSelector_IndexChanged"> <asp:ListItem value="White" selected="True">Select color...</asp:ListItem> <asp:ListItem value="Red">Red</asp:ListItem> <asp:ListItem value="Green">Green</asp:ListItem> <asp:ListItem value="Blue">Blue</asp:ListItem> </asp:DropDownList> </form> </body> </html>The page simply contains a DropDownList control, which automatically posts back each time a new item is selected. It has 3 different colors, besides the default one, which is simply white. Once a new item is selected, the ColorSelector_IndexChanged method is fired, from our CodeBehind file:
using System; using System.Data; using System.Web; public partial class _Default : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) { if(Request.Cookies["BackgroundColor"] != null) { ColorSelector.SelectedValue = Request.Cookies["BackgroundColor"].Value; BodyTag.Style["background-color"] = ColorSelector.SelectedValue; } } protected void ColorSelector_IndexChanged(object sender, EventArgs e) { BodyTag.Style["background-color"] = ColorSelector.SelectedValue; HttpCookie cookie = new HttpCookie("BackgroundColor"); cookie.Value = ColorSelector.SelectedValue; cookie.Expires = DateTime.Now.AddHours(1); Response.SetCookie(cookie); } }Okay, two different parts to be explained here. First, the Page_Load method, which is called on each page request. Here we check for a cookie to tell us which background color should be used. If we find it, we set the value of our dropdown list to reflect this, as well as the background color of the page, simply by accessing the style attribute of the body tag.
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