Themes in Chapter 6 once more

dhess · June 17th, 2011, 08:25 PM

I've been working through the C# an VB versions of the Planet Wrox project and things have gone well until the Dynamically Switching Themes section(Ch.6 p.226). I couldn't get either version to switch, although the dropdown list control behaves as it should: i.e., it holds the selected value, either Monochrome or DarkGrey. Either selection leaves the theme as Monochrome.
I figured I would come back to this later and figure it out if it became necessary, and sure enough, it did. In the Navigation chapter(Ch.7 p.259), the site throws an exception on the select statement in the Page Load routine(debug=true):

Line 24: End If
Line 25:
Line 26: Select Case Page.Theme.ToLower()
Line 27: Case "darkgrey"
Line 28: Menu1.Visible = False

Line 26 is pointed to as the offending statement. The error is "Object reference not set to an instance of an object." I should mention that C# and VB both behave the same way, so whatever I've done wrong, I've at least been consistent in both projects.
I'm using Win7 Home Premium, VS Webdev Express 2010 SP1, and Firefox 4 to display the site.

Code follows(C# only):
App_Code/BasePage.cs

Code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

/// <summary>
/// Summary description for BasePage
/// </summary>
public class BasePage:System.Web.UI.Page
{
    private void Page_PreRender(object sender, EventArgs e)
    {
        if(this.Title == "Untitled Page" || string.IsNullOrEmpty(this.Title) )
        {
            throw new Exception("Page title cannot be \"Untitled Page\" or empty string");
        }
    }

    public void Page_PreInit(object sender, EventArgs e)
    {
        HttpCookie preferredTheme = Response.Cookies.Get("PreferredTheme");
        if (preferredTheme != null)
        {
            Page.Theme = preferredTheme.Value;
        }
    }

	public BasePage()
	{
        this.PreInit += new EventHandler(Page_PreInit);
        this.PreRender += new EventHandler(Page_PreRender);
	}
}

FrontEnd.Master.cs

Code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class MasterPages_FrontEnd : System.Web.UI.MasterPage
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!Page.IsPostBack)
        {
            string selectedTheme = Page.Theme;
            HttpCookie preferredTheme = Request.Cookies.Get("PreferredTheme");
            if (preferredTheme != null)
            {
                selectedTheme = preferredTheme.Value;
            }
            if (!string.IsNullOrEmpty(selectedTheme) && ThemeList.Items.FindByValue(selectedTheme) != null)
            {
                ThemeList.Items.FindByValue(selectedTheme).Selected = true;
            }
        }
        switch (Page.Theme.ToLower())
        {
            case "darkgrey":
                Menu1.Visible = false;
                TreeView1.Visible = true;
                break;
            default:
                Menu1.Visible = true;
                TreeView1.Visible = false;
                break;
        }
    }
    protected void ThemeList_SelectedIndexChanged(object sender, EventArgs e)
    {
        HttpCookie preferredTheme = new HttpCookie("PreferredTheme");
        preferredTheme.Expires = DateTime.Now.AddMonths(3);
        preferredTheme.Value = ThemeList.SelectedValue;
        Response.Cookies.Add(preferredTheme);
        Response.Redirect(Request.Url.ToString());
    }
}

web.config

Code:

<?xml version="1.0"?>

<!--
  For more information on how to configure your ASP.NET application, please visit
  http://go.microsoft.com/fwlink/?LinkId=169433
  -->

<configuration>

    <system.web>
      <compilation debug="true" targetFramework="4.0" />
      <pages theme="Monochrome" styleSheetTheme="Monochrome" ></pages>
    </system.web>

</configuration>

I've already checked my code against downloaded code from Wrox and didn't catch any relevant differences. I hope this is enough info to point me in the correct direction.My suspicions are that solving the dynamic switch problem will also clear up the server error at the same time.

Imar · June 18th, 2011, 05:50 AM

Hi there,

Take a look at the following code in the PreInit method:

Code:

HttpCookie preferredTheme = Response.Cookies.Get("PreferredTheme");

Yo're trying to read a cookie from the Response, while you should be reading it from the Request like this:

Code:

HttpCookie preferredTheme = Request.Cookies.Get("PreferredTheme");

You also need to remove the theme from web.config, or else two themes are applied at the same time.

Hope this solves the problem, and if not, please let me know.

Cheers,

Imar

dhess · June 18th, 2011, 07:46 AM

That did it. And I did do the exact same thing in the VB version. Must have suffered an attack of code blindness when reviewing the downloaded code. Thanks for your help and now onward!