How server form post-back works?

One of the most important features of the ASP.NET environment is the ability to declare controls that run on the server, and post back to the same page. Remember the days of classic ASP? We would create a form which would accept the user's input, and then we would most probably have to create another page that would accept all those inputs, either through HTTP GET or POST, and perform some kind of validation, display and action. Sometimes, even a third page was necessary to perform our actions. This wasted a lot of time and complicated things when you had to make a change. But of course, this is not necessary any more with ASP.NET. There is no need to create second pages that accept the inputs of the first, process them and so on. Form fields and other controls can be declared to run on the server, and the server simply posts the page back to itself and performs all the validation, display and actions. Our life as web developers has become a million times better. But how exactly is this done?

When a control is declared to run on the server, a VIEWSTATE is created which remembers the ID of that control, and the method to call when an action is performed. Submit event calls the JavaScript function __doPostBack (that's 2 underscore symbols in front of it). You do not write this function, instead it is generated by the ASP.NET engine and automatically included in our page. It submits the form to the same page, and accepts 2 arguments:

eventTarget: the control doing the submission
eventArgument: any additional information for the event

At least one control needs to be set to Visible, for the server to generate the __doPostBack function in our page. Even if we have numerous web controls declared to run on the server, but they are all set to Visible=false, then the javascript function will not be included and we will not be able to perform any actions.



With Best Regards,
Mitesh Mehta
Email : miteshvmehta@gmail.com
http://cc.1asphost.com/miteshvmehta/