C# .NET Webforms -> ajaxcontroltoolkit.net -> AsyncFileUpload, trigger OnClientUploadError serverside

Question

As a reference this is the control I am discussing here: AjaxControlToolKit AsyncFileUpload.

Context: maintenance on a legacy .NET webforms (codebehind) application. I am asked to show errors that occur serverside.

It is not possible to just set the label in the code behind, because the control performs an AsyncFileUpload.

As the API describes the control provides: OnClientUploadError

So I added that to the control:

<ajaxToolkit:AsyncFileUpload ID="fuImportEpAuth" runat="server"
    OnClientUploadStarted="ImportEpAuthStartUpload"
    OnClientUploadComplete="ImportEpAuthUploadComplete"
    OnUploadedComplete="fuImportEpAuth_UploadedComplete" 
    OnClientUploadError="ImportEpAuthError" />
<asp:Label ID="lblImportWccAuth" runat="server" />

And added the following javascript to the page:

function ImportEpAuthError(sender, args) {
    var errorText = args.get_errorMessage();

    var errorLabel = document.getElementById('cphContent_lblImportWccAuth');
    errorLabel.innerText = errorText;
    errorLabel.style.color = "red";
    $.unblockUI();
}

The code is performed and the label shows an errormessage.

Please focus on the: var errorText = args.get_errorMessage();

It contains this message:

Server Response Error: ' Object reference not set to an instance of an object.'

My problem or challenge is: It should show the errormessage I throw.

(This code is serverside)

try
{
    // Upload and process file
    UploadAndProcessFile(importType, fileUpload, sPath, settingsName);
}
catch (Exception ex)
{
    //throw new Exception(ex.Message, ex);
    throw new Exception("Please help me stackoverflow, I need to show this message!!!", ex);
}

If only I could fix this, then I could finish up and deliver the fix to production. I appreciate your help!

score 0 · Accepted Answer · answered Dec 12 '16 at 16:38

Removing the InnerException will result in the following message:

Server Response Error: ' Please help me stackoverflow, I need to show this message!!!'

//throw new Exception("Please help me stackoverflow, I need to show this message!!!", ex);
throw new Exception("Please help me stackoverflow, I need to show this message!!!");

I now have access to the errormessage clientside, I am now free to show it as I like.

The solution is to implement: OnClientUploadError (re)throw the exception without the innerexception.

This solution will also answer some other questions I read on stackoverflow. Please link them to this answer.

C# .NET Webforms -> ajaxcontroltoolkit.net -> AsyncFileUpload, trigger OnClientUploadError serverside

1 Answers1