ICallbackEventHandler - How to invoke a Server side code from client side script without postback in ASP.NET?

I had received above questions from my team mate, hence I thought exploring and writing a post about Call back Event.for our reference.

Now, the actual requirement is a set in the business logic (ASP.NET code) should be executed without page post back from server-side scripting. So, how client callbacks can be achieved within Server-side scripts? Yes, the answer is using ICallbackEventHandler interface with ASP.NET and JQuery scripts. Let’s understand the technique with code snippets, a simple example is taken here for explanation for ease of learning.

1.      Let’s start with Server side code changes, The ICallbackEventHandler interface is inherited to implement the RaiseCallbackEvent and GetCallbackResult methods.

public partial class _Default : System.Web.UI.Page, System.Web.UI.ICallbackEventHandler

{}

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2.      Create a reference to the CallbackEvent

string callBackRef = Page.ClientScript.GetCallbackEventReference(this, "parameter", "ReturnStatus", "");

Note: 2^nd argument "parameter" is parameter name, can be named as anything. 3rd argument "ReturnStatus" is a function name, explained at step 5 below.

3.      Register the Client side script to invoke Server side code

string callBackScript = "function ClientSideMethod(parameter,context)" + "{" + callBackRef + ";}";

Page.ClientScript.RegisterClientScriptBlock(this.GetType(),"",callBackScript,true);

Note: function name ClientSideMethod should be mentioned in client script, on click event.

4.      Next thing, Implement the RaiseCallbackEvent and GetCallbackResult methods

public string GetCallbackResult()

   {

return "Status from Callback method";

//This text is received at client script

   }

   public void RaiseCallbackEvent(string eventArgument)

   {

System.Diagnostics.EventLog.WriteEntry("Application", "Serverside script is executed");

//the expected bussines logic is implemented here, this code snippet writes into eventvwr as simple example.

   }

5.      Finally, Client side changes, Now invoke the Server side code on button click.

<div>

<input type="button" value="Invoke Server Method" onclick="ClientSideMethod('parmeter')"/>

</div>

<script type="text/javascript">

//Client Call back, This method must be implemented.

    function ReturnStatus(result, context)

    {

       alert('Called' + result);

 }

</script>

That’s it. Now you can run the application and click the Invoke button, a new log entry would be created without page postback. For detailed explanation for every step Implementing Client Callbacks Programmatically Without Postbacks in ASP.NET Web Pages

Happy Learning!