How does an UpdatePanel actually work?

Question

What is updated when an Update is triggered? What goes to the server? What comes back?

I was under the impression that only the content of the panel was transmitted to the server and back (without touching anything in the page outside the panel), but I'm experiencing strange results, probably because I don't really understand how it works exactly.

Can someone provide an easy explanation as to how exactly it works?

Answer 1

What is generated is a form submit through AJAX, which means essentially XML HTTP in the browser. When it hits the server, the server sees it as an AJAX call and it routes the Request to the correct method.

As for precisely what is sent, it is anything that the form submit should send, which can very well be information outside of the UpdatePanel. the sever then figures out what to work with and sends back a Response.

This is all well and good as theory, but you are dealing with problems not theory. What strangeness are you experiencing? If you can post, we can focus on the particulars of the problem.