see also : article on codegain.com about the same subject.
Finally, after a lot of playing around to reproduce what was happening, I found the solution. at first I had the following javascript code :
<script type="text/javascript" language="javascript">
//registers the event by adding it to the endrequests collections of the instance
//This will allow it to actually listen to the event when it happens, and execute
//the code in the onEndRequest function
function pageLoad() {
Sys.WebForms.PageRequestManager.getInstance().add_endRequest(onEndRequest);
}
//function which will execute after the C# code gets to its end
//it will then catch the exception and display it on the alert message box
//the substring is just to avoid having the full exception definition,
//and display only the message
function onEndRequest(sender, args) {
if (args.get_error() != null) {
var msg = args.get_error().message;
alert(msg.substring(msg.indexOf(":", 0) + 1));
args.set_errorHandled(true);
return false;
}
else
{ return false; }
}
</script>
then I had too buttons on the page. everytime a button with no exception is clicked, the next time, the exception shows twice, and keeps incrementing on each postback.
here’s the full code listing for the test asp.net page and C#, with the corrected javascript.
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" 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></title>
<script type="text/javascript" language="javascript">
//registers the event by adding it to the endrequests collections of the instance
//This will allow it to actually listen to the event when it happens, and execute
//the code in the onEndRequest function
function pageLoad() {
Sys.WebForms.PageRequestManager.getInstance().remove_endRequest(onEndRequest); //>>Key line of code for the correction
Sys.WebForms.PageRequestManager.getInstance().add_endRequest(onEndRequest);
}
//function which will execute after the C# code gets to its end
//it will then catch the exception and display it on the alert message box
//the substring is just to avoid having the full exception definition,
//and display only the message
function onEndRequest(sender, args) {
if (args.get_error() != null) {
var msg = args.get_error().message;
alert(msg.substring(msg.indexOf(":", 0) + 1));
args.set_errorHandled(true);
return false;
}
else
{ return false; }
}
</script>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:ScriptManager runat="server" ID="script1" />
<asp:UpdatePanel runat="server" ID="pnlExceptions">
<ContentTemplate>
<h4>Exceptions thrown from C#, and displayed in a javascript alert box (works with the update panel)</h4>
<asp:Button runat="server" ID="txtExceptionInAlert" Text="Trigger Exception" OnClick="txtExceptionInAlert_Click" />
<asp:Button ID="Button1" runat="server" Text="Asynchronous post back button" />
</ContentTemplate>
</asp:UpdatePanel>
</div>
</form>
</body>
</html>
using System;
public partial class _Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
}
/// <summary>
/// throwing the exception at the click event
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
protected void txtExceptionInAlert_Click(object sender, EventArgs e)
{
throw new Exception("This is an exception thrown from C# code");
}
}
To Reproduce the error, comment this line in the PageLoad : Sys.WebForms.PageRequestManager.getInstance().remove_endRequest(onEndRequest);
the thing, is that in Javascript, I wonder how we can tell it it’s a postback, and not a new pageLoad.
Hope this helps !
