Introduction to ASP .Net Post back:
Programming model in old ASP for using POST method in form is to post the values of a Form to a second page. The second asp page will receive the data and process it for doing any validation or processing on the server side.
With ASP .Net, the whole model has changed. Each of the asp .net pages will be a separate entity with ability to process its own posted data. That is, the values of the Form are posted to the same page and the very same page can process the data. This model is called post back.
Each Asp .net page when loaded goes through a regular creation and destruction cycle like Initialization, Page load etc., in the beginning and unload while closing it. This Postback is a read only property with each Asp .Net Page (System.Web.UI.Page) class. This is false when the first time the page is loaded and is true when the page is submitted and processed. This enables users to write the code depending on if the PostBack is true or false (with the use of the function Page.IsPostBack()).
Implementation of ASP.Net Post back on the Client side:
Post back is implemented with the use javascript in the client side. The HTML page generated for each .aspx page will have the action property of the form tag set to the same page. This makes the page to be posted on to itself. If we check the entry on the HTML file, it will look something like this.
<form name=”_ctl1″ method=”post” action=”pagename.aspx?getparameter1=134″ language=”javascript” onsubmit=”if (!ValidatorOnSubmit()) return false;” id=”_ctl1″ >
Also, all the validation code that is written (Required Field Validation, Regular Expression validation etc.,) will all be processed at the client side using the .js(javascript) file present in the webserver_wwwroot/aspnet_client folder.
With this new ASP .Net model, even if the user wants to post the data to a different .aspx page, the web server will check for the runat=’server’ tag in the form tag and post the web form to the same .aspx page. A simple declaration as in the following code snippet will be enough to create such a web form.
<form id=”form1″ runat=”server” >
<!– place the controls inside –>
</form>