Avoiding unnecessary server work in ASP.Net

[This was originally posted at http://timstall.dotnetdevelopersjournal.com/avoiding_unnecessary_server_work_in_aspnet.htm]

One of the best ways to increase performance in ASP.Net pages is to not do any unnecessary server-side work. For example, every postback and callback will re-trigger the entire Page's server life cycle - rerunning OnInit, OnLoad, OnPreRender, etc... However, a server-side action only require a fraction of the original code to run - for example clicking a button may not require you to repopulate all dropdowns.

Concept	Example	Details
Is Postback	Clicking an ASP.Net button postbacks the page	this.IsPostBack
Is Callback	A JavaScript triggers an ASP.Net 2.0 callback	this.IsCallback
Is Redirecting	A method has called Response.Redirect, but there is still heavy processing (that is now unnecessary) that will still be called.	Response.IsRequestBeingRedirected
Is Ajax update panel postback	A button within an Ajax update panel has been clicked, but don't redo server work outside of that update panel	public static bool IsPartialPostback(System.Web.UI.Page p) { return ((System.Web.UI.ScriptManager.GetCurrent(p) != null) && (System.Web.UI.ScriptManager.GetCurrent(p).IsInAsyncPostBack)) }
Is Button click	User clicks exit button - no need to repopulate dropdowns	Request["__EVENTTARGET"] //indicates which event (like a button) triggered the postback.