Setting up a Asp.net page for callback

November 27, 2012 Uncategorized Comments Off on Setting up a Asp.net page for callback

On my current project I wanted to add simple callback functionally. After searching google for a while and finding various solutions that I couldn’t get to work I came across the following posting from Microsoft:

Implementing Client Callbacks Programmatically Without Postbacks in ASP.NET Web Pages

It was very straight forward and I was able to get my callback going.

The following is the code behind that I used to get it working:

  void Page_Load(object sender, EventArgs e) {
    PageCallbackSetup();
  }
 
  /// <summary>
  /// Setup for the callback for a page
  /// </summary>
  private void PageCallbackSetup() {
    var cm = Page.ClientScript;
 
    // Client side function that will be executed when callback is finished
    var cbReference = cm.GetCallbackEventReference(this, "arg", "ReceiveServerData", "");
 
    // Function that is called to start the callback to the server
    var callbackScript = "function CallServer(arg) {" + cbReference + "; }";
 
    // Register script with the page for the callback
    cm.RegisterClientScriptBlock(this.GetType(), "CallServer", callbackScript, true);
  }
 
  #region ICallbackEventHandler Members
 
  /// <summary>
  /// Returns result to client
  /// </summary>
  /// <returns>string of results from the server</returns>
  public string GetCallbackResult() {
    return "This is the time from the callback: " + DateTime.Now.ToString();
  }
 
  /// <summary>
  /// Raised when the callback takes place
  /// </summary>
  public void RaiseCallbackEvent(string eventArgument) {
  }
 
  #endregion

The following is the HTML markup:

<%@ Implements Interface="System.Web.UI.ICallbackEventHandler" %>
 
<!doctype html>
<html lang="en">
<head runat="server">
  <title></title>
  <script type="text/javascript">
    function ReceiveServerData(arg) {
      MessageFromServer.innerText = arg;
    }
  </script>
</head>
<body>
  <form id="form1" runat="server">
  <div>
    <input type="button" value="Callback" onclick="CallServer('CallSubmittedFrom')" />
    <br />
    <span id="MessageFromServer"></span>
  </div>
  </form>
</body>
</html>

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