Chapter 7 page261 as it relate to Chapter6 page223

skijor · August 3rd, 2009, 12:54 AM

Hello Imar,

I'm a little confused between Server.Transfer and Response.Redirect. I tried to use Server.Transfer instead of Response.Redirect on page 223 just to see what would happen, and it's not what I expected, and I can't come up with an explanation. For example I select "DarkGrey" and I see "DarkGrey in the variable "preferredTheme" and it actually does add the cookie with a value of "DarkGrey" (as I expected).

Code:

protected void lstPreferredTheme_SelectedIndexChanged(object sender, EventArgs e)
    {
           HttpCookie preferredTheme = new HttpCookie("PreferredTheme");
            preferredTheme.Expires = DateTime.Now.AddMonths(3);
      preferredTheme.Value = lstPreferredTheme.SelectedValue;
      Response.Cookies.Add(preferredTheme);
            //Response.Redirect(Request.Url.ToString());
      Server.Transfer(Request.Url.PathAndQuery);
    }

When I get to the code below and after the cookie request, the preferredTheme is still "Monochrome" (Something I did not expect). If I close the website and reopen it it shows "DarkGrey"

Code:

private void Page_PreInit(object sender, EventArgs e)
  {
    HttpCookie preferredTheme = Request.Cookies.Get("PreferredTheme");
    
    if (preferredTheme != null)
    {
      // Test to see if theme is still available (maybe it's been discontinued)
      string rootPath = Server.MapPath("~/App_Themes");
      var theme = System.IO.Directory.GetDirectories(rootPath, preferredTheme.Value);
      if (theme.Length > 0)
      {
        Page.Theme = preferredTheme.Value;
      }
    }
  }

Can you help me understand what is going on?

Thank you.

Imar · August 3rd, 2009, 01:22 PM

Hi there,

Server.Transfer takes place at the server, so the Request collection with your new cookie is not updated. Here's what the code / page does:

1. Handle DDL change
2. Add cookie to Response.Cookies
3. Transfer to new page
4. This new page sets the theme based on Request.Cookies which still contains the old value
5. The browser receives the cookie in Response.Cokkies and submits it with the next request in Request.Cookies.

To see what I mean set a breakpoint in the Transfer line and add the following to your Watch window:
Response.Cookies["PreferredTheme"].Value
Request.Cookies["PreferredTheme"].Value

You'll see the two cookie collections contain different values.

Hope this helps,

Imar

skijor · August 4th, 2009, 01:27 PM

Thanks Imar,

I finally get it.

Imar · August 5th, 2009, 08:59 AM

You're welcome. Glad I could help...

Imar