Update pane that does not display errors in ASP.NET 3.5

Question

In Visual Studio 2008, if you create a new "Ajax 1.0 Enabled ASP.NET 2.0 Web Application" and paste the following code:

<form id="form1" runat="server"> <asp:ScriptManager ID="ScriptManager1" runat="server" /> <div> <asp:UpdatePanel ID="UpdatePanel1" runat="server"> <ContentTemplate> <asp:Button runat="server" ID="foo" Text="click me" onclick="foo_Click" /> </ContentTemplate> </asp:UpdatePanel> </div> </form> 

code for

 protected void foo_Click(object sender, EventArgs e) { throw new Exception("hello"); } 

and then click the button, you will see a javascript warning saying "hello". If you create a .NET 3.5 web application and paste the same code, an alert no longer appears. What am I missing?

Answer 1

A change has been defined between the default behavior in ASP.NET AJAX Extensions 1.0 and ASP.NET AJAX 3.5. This can be seen by looking at the default endPostBack event handlers for Sys.WebForms.PageRequestManager. In the previous version, an error is displayed with a warning, and later the error is simply repeated.

 // ASP.NET AJAX Extensions 1.0 function Sys$WebForms$PageRequestManager$_endPostBack(error, response) { this._processingRequest = false; this._request = null; this._additionalInput = null; var handler = this._get_eventHandlerList().getHandler("endRequest"); var errorHandled = false; if (handler) { var eventArgs = new Sys.WebForms.EndRequestEventArgs(error, this._dataItems, response); handler(this, eventArgs); errorHandled = eventArgs.get_errorHandled(); } this._dataItems = null; if (error && !errorHandled) { alert(error.message); } } // ASP.NET 3.5 function Sys$WebForms$PageRequestManager$_endPostBack(error, executor, data) { if (this._request === executor.get_webRequest()) { this._processingRequest = false; this._additionalInput = null; this._request = null; } var handler = this._get_eventHandlerList().getHandler("endRequest"); var errorHandled = false; if (handler) { var eventArgs = new Sys.WebForms.EndRequestEventArgs(error, data ? data.dataItems : {}, executor); handler(this, eventArgs); errorHandled = eventArgs.get_errorHandled(); } if (error && !errorHandled) { throw error; } } 

If you want Alert to appear in your ASP.NET AJAX 3.5 code, you just need to make small changes.

First you need to add the AsyncPostBackError ScriptManager event handler, and then install AsyncPostBackErrorMessage.

 protected void ScriptManager1_AsyncPostBackError(object sender, AsyncPostBackErrorEventArgs e) { ScriptManager1.AsyncPostBackErrorMessage = e.Exception.Message; } 

Then you need to add a handler for the endRequest event on the client side of the PageRequestManager. There you can install AsyncPostBackErrorMessage on the server side and use an alert to display a message to the user.

 function pageLoad() { Sys.WebForms.PageRequestManager.getInstance().add_endRequest(onEndRequest); } function onEndRequest(sender, args) { var msg = args.get_error().message; alert(msg); args.set_errorHandled(true); } 

Hope this helps.

Answer 2

If you just want to fix the JavaScript error in JavaScript and display an exception message for the user, you just need to add this to your main page somewhere after the form declaration:

 <!-- This script must be placed after the form declaration --> <script type="text/javascript"> Sys.Application.add_load(AppLoad); function AppLoad() { Sys.WebForms.PageRequestManager.getInstance().add_endRequest(EndRequest); } function EndRequest(sender, args) { // Check to see if there an error on this request. if (args.get_error() != undefined) { var msg = args.get_error().message.replace("Sys.WebForms.PageRequestManagerServerErrorException: ", ""); // Show the custom error. // Here you can be creative and do whatever you want // with the exception (ie call a modalpopup and show // a nicer error window). I will simply use 'alert' alert(msg); // Let the framework know that the error is handled, // so it doesn't throw the JavaScript alert. args.set_errorHandled(true); } } </script> 

You do not need to catch OnAsyncPostBackError, even if you do not want to customize the message. Go to my blog post if you want more information about this.