Tuesday, September 4, 2007

How to Register Stylesheet Created in Runtime

Here is an example from MSDN:
// Create a Style object for the  section of the Web page.
Style bodyStyle = new Style();
bodyStyle.ForeColor = System.Drawing.Color.Blue;
bodyStyle.BackColor = System.Drawing.Color.LightGray;
// Add the style to the header of the current page.
Page.Header.StyleSheet.CreateStyleRule(bodyStyle, this, "BODY");

It is the simple and handy method but has a few flaws.
1. Output is far from optimal. For example, following code that adds a border
someStyle.BorderColor = System.Drawing.Color.Red;
someStyle.BorderStyle = BorderStyle.Solid;
someStyle.BorderWidth = new Unit("1px");
produces this output
instead of
border:Solid 1px Red;

It has no matter if you don't pay attention to the size of pages you develop, but it is taken into consideration if you take into consideration your visitor's needs (sorry for tautology). But it's a trifle, of course. I mentioned it just for completeness. There is a more serious flaw.

2. Number of style attributes that can be registered in such way is very limited. You can't add padding or margin attributes or even particular border (e.g. border-left).

The code overview

Class StylesController has four public static methods:
//includes registered styles into page header
public static void RegisterStyleSheetBlock(Page page, string key, string styles)
LiteralControl ctrl = new LiteralControl(string.Format(@"<style type=""text/css"">
</style>", styles));
ctrl.ID = key;
//includes link to the newly created stylesheet file into page header
public static void RegisterStyleSheetInclude(Page page, string key, string styles)
byte[] bytes = System.Text.Encoding.UTF8.GetBytes(key);
string base64Key = Convert.ToBase64String(bytes).Replace('+', '!');
LiteralControl ctrl = new LiteralControl(string.Format(@"<link
type=""text/css"" rel=""stylesheet"" href=""{0}?key={1}""/>",
ctrl.ID = key;
HttpContext.Current.Session[base64Key] = styles;
//checks whether inline styles with specified key have been already registered
public static bool IsStyleSheetBlockRegistered(Page page, string key)
return (page.Header.FindControl(key) != null);
//checks whether a file with styles with specified key have been already registered
public static bool IsStyleSheetIncludeRegistered(Page page, string key)
return (page.Header.FindControl(key) != null);
The class StylesController implements IHttpHandler interface and serves as HttpHandler that produces the stylesheet file.
public class StylesController : IHttpHandler, System.Web.SessionState.IRequiresSessionState 
#region IHttpHandler Members
bool IHttpHandler.IsReusable
get { return false; }
void IHttpHandler.ProcessRequest(HttpContext context)
context.Response.ContentType = "text/css";
string key = context.Request["key"];
if (key != null)
object script = context.Session[key];
if (script != null)
HttpHandler has to be registered in web.config
<add verb="GET" path="StyleSheet.css" type="TypeName, AssemblyName"/>

where AssemblyName is the name of the assembly, where the class StylesController is located,
TypeName is the fully qualified name of the StylesController, including the namespace.

How to use

string styles = "div{padding:2px 5px;background-color:red;}";
if (!StylesController.IsStyleSheetBlockRegistered(this, "Red Divs"))
StylesController.RegisterStyleSheetBlock(this, "Red Divs", styles);
string styles2 = "a,a:link {text-decoration:none;background-image:url(img/back.gif);}";
if (!StylesController.IsStyleSheetIncludeRegistered(this, "New Links"))
StylesController.RegisterStyleSheetInclude(this, "New Links", styles2);

Source code - 1kB

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