What is the Difference Between Postback and Callback in Asp.NET

Question

Hi What is the difference between Postback and callback in Asp.NET ?

Satyapriya Nayak · Answer

Hi Arun Callback : It is a way to send a request to the web page from the client script. Postback is an expensive call with processing overhead. In callback a client function sends a request and a special marked method is invoked on the server. It does the processing & returns the value which is received by another client function to process the result. To have client side callbacks the page has to implement ICallbackEventHandler & implement functions RaiseCallBackEvent & GetCallBackResult. PostBack: Postback is the event which sends the form data to the server. The server processes the data & sends it back to the browser. The page goes through its full life cycle & is rendered on the browser. It can be triggered by using the server controls. A Postback occurs when the data (the whole page) on the page is posted from the client to the server..ie the data is posted-back to the server  and thus the page is refreshed (redrawn)...think of it as ' sending the server the whole page (asp.net) full of data '. On the other hand a callback is also a special kind of postback  but it is just a quick round-trip to the server to get a small set of data (normally) and thus the page is not refreshed unlike with the postback...think of it as ' calling the server and receiving some data back ' With Asp.Net the ViewState is not refreshed when a callback is invoked  unlike with a postback. Please refer the below links http://wiki.answers.com/Q/Difference_between_callback_and_postback_in_asp_net http://www.dotnetfunda.com/interview/exam717-what-is-difference-between-callbacks-and-postback-in-aspnet.aspx Thanks

Vulpes · Answer

There's a good explanation of the difference between the two in this SO thread: http://stackoverflow.com/questions/365100/difference-between-a-postback-and-a-callback