C# 4 and .NET 4

Themes ❘ 1209
This sort of theme is useful in, for example, printable versions of web pages. The BareTheme directory
actually consists of no files at all — the only file in use here is the root StyleSheet.css style sheet.
The demo site also contains a third theme, called LuridTheme. This brightly colored and difficult-to-read
theme is just a bit of fun, really, but it does show how the look of a site can be dramatically changed
using themes. On a more serious note, themes similar to this can be used to provide high-contrast or largetext
versions of web sites for accessibility purposes.
In PCSDemoSite, the currently selected theme is stored in session state, so the theme is maintained when
you navigate around the site. The code-behind file for /Configuration/Themes/Default.aspx is as
follows:
public partial class _Default : MyPageBase
{
private void ApplyTheme(string themeName)
{
if (Session["SessionTheme"] != null)
{
Session.Remove("SessionTheme");
}
Session.Add("SessionTheme", themeName);
Response.Redirect("~/Configuration/Themes", true);
}
void applyDefaultTheme_Click(object sender, EventArgs e)
{
ApplyTheme("DefaultTheme");
}
void applyBareTheme_Click(object sender, EventArgs e)
{
ApplyTheme("BareTheme");
}
}
void applyLuridTheme_Click(object sender, EventArgs e)
{
ApplyTheme("LuridTheme");
}
code snippet PCSDemoSite/Configuration/Themes/Default.aspx.cs
The key functionality here is in ApplyTheme(), which puts the name of the selected theme into session state,
using the key SessionTheme. It also checks to see if there is already an entry here, and if so, removes it.
As mentioned earlier, themes must be applied in the Page_PreInit() event handler. This isn’t accessible
from the master page that all pages use, so if you want to apply a selected theme to all pages, you are left
with two options:
➤
➤
Override the Page_PreInit() event handler in all pages where you want themes to be applied.
Provide a common base class for all pages where you want themes to be applied, and override the
Page_PreInit() event handler in this base class.
PCSDemoSite uses the second option, with a common page base class provided in Code/MyPageBase.cs:
public class MyPageBase : Page
{
protected override void OnPreInit(EventArgs e)
{
// theming
if (Session["SessionTheme"] != null)
{
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