How does Ajax UpdatePanel let only refresh perticular part of page

I got this question in Interview for post of SSE in ASP.NET. the interview asked me that which control u use to not get your full page refresh when u click on button. i answered that we use Ajax updatepane开发者_运维技巧l for it. then he asked that explain that how does updatepanel do it happen.

I think an update panel hooks the submit event and generates an asynchronous request instead. It manages the request/response by System.Web.Handlers.ScriptModule that is an HTTPModule. This module acts on the asyc request which are caused by UpdatePanel. It renders the update panel and writes the result to the response at the end. Check this post out. It's not what exactly an update panel does. But demonstrates how you can use an HTTPModule to update a portion of a page, ViewState and EventValidation like an UpdatePanel.

http://mgolchin.blogspot.com/2009/09/custom-control-with-partial-rendering.html