Chapter 10, Cookies

McMug · March 29th, 2004, 01:51 AM

Hi,

After I run the cookie1.aspx file, and I can't find the background cookie file anywhere in my harddrive.

Also, I closed my browser after I ran the cookies1.aspx file and set the background color to red and closed my browser and I got an error when I try to run cookie2.aspx. Looks like the background cookie didn't stored to my cookies' folder, and when cookie2.aspx try to reference it, it generated an errors saying can't reference a null object. Please help anyone.

Thanks!

Imar · March 29th, 2004, 02:55 AM

Hi there,

Can you please post the code? Not everyone has the book, so it's hard to see where the problem is without seeing some of the code.

Cheers,

Imar

---------------------------------------
Imar Spaanjaars
Everyone is unique, except for me.

McMug · March 29th, 2004, 03:12 PM

thanks for your help! here are the code for both cookie1.aspx and cookie2.aspx.

Cookie1.aspx

<%@ Page Language="c#" %>
<script Language="c#" runat="server">
  void Page_Load(object source, EventArgs e)
  {
    if (!(IsPostBack))
    {
      MyButton.Text = "Save Cookie";
      MyDropDownList.Items.Add("Blue");
      MyDropDownList.Items.Add("Red");
      MyDropDownList.Items.Add("Gray");
    }
  }
  public void Click(object sender, EventArgs e)
  {
    HttpCookie MyCookie = new HttpCookie("Background");
    MyCookie.Value = MyDropDownList.SelectedItem.Text;
    Response.Cookies.Add(MyCookie);
  }

</script>

<html>
  <body>
    <form id="CookieForm" method="post" runat="server">
      <asp:DropDownList id=MyDropDownList runat="server"/>
      <asp:button id=MyButton runat="server" OnClick="Click"/>
    </form>
  </body>
</html>

Cookie2.aspx

<%@ Page Language="c#" %>
  <script Language="c#" runat="server">
    void Page_Load(object source, EventArgs e)
    {
      Response.Cache.SetExpires(DateTime.Now);
    }
    string GetBackground()
    {
      return Request.Cookies["Background"].Value;
    }
  </script>
  <html>
    <body bgcolor="<% Response.Write(GetBackground()); %>">
    <asp:label id="message" runat="server" />
    </body>
  </html>

Imar · March 30th, 2004, 04:03 AM

It looks like you haven't set the Expires property of the cookie. If you don't provide a date to this property, the cookie will only last for the current browser session (it's not saved to disk, and deleted when you close the last browser window).

On Cookie1.aspx, make the cookie last 30 minutes with this code (from the MSDN page I linked to in this post):

Code:

DateTime dt = DateTime.Now;
TimeSpan ts = new TimeSpan(0, 0, 30, 0);

HttpCookie MyCookie = new HttpCookie("Background");

MyCookie.Value = MyDropDownList.SelectedItem.Text;
MyCookie.Expires = dt.Add(ts);

Response.Cookies.Add(MyCookie);

This way, even if you close the browser, the cookie will last for 30 minutes (by saving it to disk).

You should also never assume that a cookie exists. That means that on Cookie2,aspx, you should find out if the cookie is null or not. If it isn't, retrieve and use its value, otherwise make up a (default)value, or skip the code entirely:

Code:

string GetBackground()
{
  if (Request.Cookies["Background"] != null)
  {
    return Request.Cookies["Background"].Value;
  }
  else
  {
    // Cookie does not exist. Return a default value
    return "#ffffff";
  }
}

This way, even if the cookie doesn't exist, you won't get an error, but you get the default background color instead.

Does this help?

Imar

---------------------------------------
Imar Spaanjaars
Everyone is unique, except for me.