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LiveCallback ASP.NET Server Control Information

This page includes information about the LiveCallback Server Control, which is included in PowerWEB LiveControls for ASP.NET:

[View LiveControl Demo]

While remote-scripting functionality required by most web applications is encapsulated by the other controls included with LiveControls for ASP.NET, there are times when a more custom callback is required. For these purposes, the LiveCallback control is used. The LiveCallback control is used to call a server function (and get the return value from the function) from the browser without refreshing the page. Simply drag a LiveCallback control on a webform, create the server function to call, then call the client-side "pwBeginCallServerFunction" function and a callback is transparently sent to the server, calling the function, and returning the value to the client.

Remember! Any LiveControl which raises a callback to the server (such as LiveCallback) raises a server event within which ANY client-side element can be visually updated without refreshing the page!

The LiveCallback control has the following features:

  • Cross-browser compatible, no plugins, downloads, or security warnings.
  • From client-side script, call a server function without refreshing the page.
  • Pass up to 9 parameters into the server function.
  • Operates as a transparent, background operation.

Some example uses for LiveCallback:

  • Pass data transparently to the server as needed.
  • Create a text "autosave" feature which works in the background while the user fills out a textbox.
  • Create custom your own custom LiveControls by wiring a server-side function to a client-side event.


Browser Compatibility

LiveControls have been tested and are fully "callback-compatible" in the following browsers:

  • Microsoft Internet Explorer 5.0+ for Windows
  • Microsoft Interner Explorer 5.0+ for Macintosh
  • Netscape 7.1+ for Windows
  • Netscape 7.1+ for Macintosh OS X
  • Mozilla 1.3+ for Windows
  • Mozilla 1.3+ for Macintosh OS X
  • Firefox for Windows
  • Firefox for Macintosh OS X
  • Camino for Macintosh OS X
  • Konqueror based engines
  • Galeon
  • Opera 5.0+

If a browser which is not compatible accesses a page containing LiveControls, the controls will fall back to the standard ASP.NET functionality. For example, a LiveButton issues a transparent callback when clicked. If on a non-compatible page, the button will still be displayed, but will cause a standard postback when clicked.

Server Tag Example

The following code demonstrates the server tags and JavaScript required to call a server function.

<script language="javascript">
function doCallback(){
   pwBeginCallServerFunction("ServerFunction", "clientFunction", "", false);
function clientFunction(response){
<input type="button" value="Click me" onclick="doCallback()">
<cc1:LiveCallback id="LiveCallback1" runat="server"></cc1:LiveCallback>

Code-Behind Example

This code demonstrates an example server function to call from the client-side.

public string ServerFunction()
   return "This is from the server.";