Reload Current Page In Asp.net?

I have a session variable that changes some things about how a page looks. I have a button that changes the value of this session variable. But ... the onClick event happens after page load, so by the time I update the session variable based on the button click, it's too late, the page has already been loaded.

Theoretically I could put all the logic about changing the display into a function and call it from page load, and then call it again from the onclick after the variable as been updated. But this is impractical: there are many user controls that check the value, used on many different pages in different combinations. I would have to hard-code the list of user controls on each page, and if someone added a new user control to a particular page, they'd have to remember to update this function, which is lame.

Is there a way to force a page reload? (I can use response.redirect back to myself and it works. If all else fails I guess this is what I'll do. But it means an extra round trip to the server, which is clumsy.)

Is there a way to process the onclick before the page load?