----------------------------------------------------------- New Message on MumbaiUserGroup
----------------------------------------------------------- From: Swapnil_B1 Message 1 in Discussion Client Call Back in ASP.NET 2.0 ASP.NET 2.0 includes a new Client Callback feature that enables you to retrieve page values and populate them to an already-generated page with out reconstructing page. This makes it possible to use on a page with out going through the entire post back cycle; that means you can update your pages without completely redrawing the page. End users will not see the page flicker and reposition, and the pages will have a flow of a thick client application. It is an interesting feature that allows invoking server side code from Client side JavaScript using XmlHTTP. Postback and Callback Before we appreciate the feature of Callback, let's see how current Postback feature in a typical ASP.NET page works. In a normal Postback situation, when any page event is triggered on ASP.NET page, a HTTP post request will be sent to web server, which then processes the request with the IPostbackEventHandler and runs the request through a series of page events. These events include loading the state (ViewState), processing data, processing Postback events and finally rendering the page to be interpreted by the consuming browser. This process completely reloads the page in the browser, which is what causes the flicker and the realignment to the top of the page. But in a Client call back situation, any page event is triggered on ASP.NET page; it causes the event to be posted to a script event handler (a JavaScript function) that sends off an asynchronous request to the web server for processing. ICallbackEventHandler runs the request through a pipeline similar to what is used with the Postback- but you notice that some of the larger steps (such as rendering the page) are excluded from the process chain. After the information is loaded, the result is returned to the script callback object. The script code then pushes this data into the web page using JavaScript's capabilities to do this without refreshing the page. Let's see an example to see how Callback feature works. Following page will generate Current date when end user clicks the button on the form, the callback service is initiated and current date is populated into the textbox. <%@ Page Language="VB" AutoEventWireup="false" CodeFile="Default.aspx.vb" Inherits="_Default" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd";> <html xmlns="http://www.w3.org/1999/xhtml"; > <head runat="server"> <title>Client Callback</title> <script type="text/javascript" > function GetDate() { UseCallback(); } function GetDateFromServer(TextBox1, context) { document.forms[0].TextBox1.value= TextBox1; } </script> </head> <body> <form id="form1" runat="server"> <div> <input id="Button1" type="button" onclick="GetDate()" value="Get Date" /> <br /> <br /> <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox> </div> </form> </body> </html><o:p></o:p> Partial Class _Default Inherits System.Web.UI.Page Implements System.Web.UI.ICallbackEventHandler Dim _callbackResult As String = Nothing Public Function GetCallbackResult() As String Implements System.Web.UI.ICallbackEventHandler.GetCallbackResult Return _callbackResult End Function Public Sub RaiseCallbackEvent(ByVal eventArgument As String) Implements System.Web.UI.ICallbackEventHandler.RaiseCallbackEvent _callbackResult = Now.ToString() End Sub Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load Dim cbReference As String = Page.ClientScript.GetCallbackEventReference(Me, "arg", "GetDateFromServer", "context") Dim cbScript As String = "function UseCallback(arg,context)" & _ "{" & cbReference & ";" & "}" Page.ClientScript.RegisterClientScriptBlock(Me.GetType(), "UseCallback", cbScript, True) End Sub End Class Swapnil (Swaps) http://swapsnet.spaces.live.com/ ----------------------------------------------------------- To stop getting this e-mail, or change how often it arrives, go to your E-mail Settings. http://groups.msn.com/MumbaiUserGroup/_emailsettings.msnw Need help? If you've forgotten your password, please go to Passport Member Services. http://groups.msn.com/_passportredir.msnw?ppmprop=help For other questions or feedback, go to our Contact Us page. http://groups.msn.com/contact If you do not want to receive future e-mail from this MSN group, or if you received this message by mistake, please click the "Remove" link below. On the pre-addressed e-mail message that opens, simply click "Send". Your e-mail address will be deleted from this group's mailing list. mailto:[EMAIL PROTECTED]
