Need to access the Page object in Global.asax in the PreRequestHandlerExecute

I have a huge website (containing around 5000+) pages. There is a theme functionality in the website where user can choose different colors for their profil开发者_开发百科e. Now i want to use the ASP.net theme feature and put different CSS (for different colors) in the theme folder and in Global.asax i want check the user theme and render appropriate link element with the css. But my problem is, i am not able to access the Page element for adding the link in the page. Here is my code

Dim page As System.Web.UI.Page = TryCast(System.Web.HttpContext.Current.Handler,System.Web.UI.Page)
page.StyleSheetTheme = "Black"

But when i run this code I get a Null reference error.

P.s : My application is very huge so its not possible to have a master page or a base class and inherit it in every page.

Please suggest.

The page is not available in PreRequestExecute. This function is called before asp.net steps in to handle things, and asp.net is responsible for the page. Think of PreRequestExecute as being earlier in the scheme of things, like when IIS is first trying to figure out what to do with this thing it has, the thing is not even a page yet.

You might want to look into some of the other events that you can hook, there are events that would take place after the page has loaded that may allow you to do what you are suggesting.

Rather than going into global.asax for this, consider using master pages. One possibility is to have nested master pages, where the first master page sets up overall layout, and the nested master handles the theme. (Or one of several nested master pages, all referencing the same top-level master page). If necessary, you can use the PreInit event in the page to change master pages, and select the master that matches your theme selection.

You can centralize this function by having your own class that inherits System.Web.UI.Page, and have all your own pages inherit this new class. Handle the PreInit event there. (As well as other useful functions, like page-level handling of unhandled exceptions, general security issues, etc.

EDITED TO ADD: As @aepheus correctly notes, the page hasn't been instantiated at the PreRequestHandlerExecute event. So there's no page class you can access.