How to register async method in ASP.NET WebForms project deployed to Azure Web App?

Question

I'm trying to implement an async call in an ASP.NET WebForms page. I can do this by either registering the async method:

RegisterAsyncTask(new PageAsyncTask())

or adding async to page load:

protected async void Page_Load(object sender, EventArgs e)

In either case, when I access the page in a browser I get the following error:

Task-returning Page methods are unsupported in the current application configuration. To work around this, remove the following configuration switch in Web.config: <appSettings> <add key="aspnet:UseTaskFriendlySynchronizationContext" /> </appSettings>

If I remove this from the web.config (or set the value to "true") everything works as expected. However, when I deploy the code to an Azure Web App, I get the error:

System.InvalidOperationException: <%@ Page AspCompat="true" %> and are unsupported in the current application configuration. To work around this, add the following configuration switch in Web.config: <appSettings> <add key="aspnet:UseTaskFriendlySynchronizationContext" value="false" />

So you can see the problem is that the async method needs UseTaskFriendlySynchronizationContext="true", but the Azure Web App environment needs UseTaskFriendlySynchronizationContext="false". How can I resolve this?

What exactly do you want to execute asynchronously? Usually that’s a red flag IMHO as people tend to do the wrong things there. — Lex Li
– Lex Li, Commented Oct 24, 2024 at 14:39

Harshitha Veeramalla · Accepted Answer · 2024-10-29 12:21:57Z

Thanks @mason for the comments.

Even I got the same error.

Error with false value,

_Task-returning Page methods are unsupported in the current application configuration. To work around this, remove the following configuration switch in Web.config:  
<appSettings>  
<add key="aspnet:UseTaskFriendlySynchronizationContext" />  
</appSettings>  
For more information, see http://go.microsoft.com/fwlink/?LinkId=252465._

Error with true value

 _This_operation requires the page to be asynchronous (the Async attribute must be set to true)._

Error message clearly says to add Async="true" in the .aspx file.
As suggested in the error message added Async="true" in the .aspx Page directive.

<%@ Page Title="Home Page" Language="C#" MasterPageFile="~/Site.Master" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="ASPForms._Default" Async="true" %>

Now, I am able to access the app without appsetting UseTaskFriendlySynchronizationContext key as well as with value="true" with Async="true" in .aspx page.
Deployed the app without the appsetting and able to access it without any issues.

enter image description here

but the Azure Web App environment needs UseTaskFriendlySynchronizationContext="false"

If you want to add the appsetting based on your environment, then you can use Web.config Transformation.

enter image description here

Web.config for Local and Web.Release.config for Azure App service (Production).

Web.Release.config:

  <appSettings>
    <add key="aspnet:UseTaskFriendlySynchronizationContext" value="false" xdt:Transform="SetAttributes" xdt:Locator="Match(key)" />
  </appSettings>

Collectives™ on Stack Overflow

How to register async method in ASP.NET WebForms project deployed to Azure Web App?

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related