- When an input control is associated with a server event, ASP.net renders it to the client browser with a JavaScript function attached.
- Additionally, there are few hidden variables rendered in the page to store the control name and arguments related to an event.
- The generic function, attached to the control, exists as __doPostBack with eventTarget and eventArguments that can accommodate the input control’s name and any associated arguments. This function, __doPostBack, fills the hidden variables and does a form submit to the server.
- The server when receives the form data, it decodes from hidden variables to identify the control that invoked the server postback and calls the appropriate server event method.
A much more detailed information is available here:
http://sanalksankar.blogspot.com/2009/12/event-asp-net-form-submit-postback-page.html
