asp.net webforms control not updating after being modified in httpclient call/response

I'm trying to make a quick and dirty c# asp.net webforms app. Nothing fancy.

new webforms project, open the designer for default.aspx.cs

Then drag a button and a textbox off the toolbar onto the page.

Then double-click on the button in the designer to get the click method and it's 100% reproducible. The app is literally as simple as you can get.

This may be a really basic issue, I suspect it's an update on another thread issue.

In my default.aspx.cs file, I'm hitting a webAPi, getting "OK" back. I want the text of the textbox1 to change from "?" to "OK" returned from the web service.

I click the button everything executes as expected, I see the text get changed in the debugger, but on the webpage it's still the old "?" value.

I'm guessing it's because I'm updating it in a response on a different thread?

protected void Button1_Click( object sender, EventArgs e )
        {
            try
            {
                // Create an HttpClient instance 
                HttpClient client = new HttpClient();

                // Send a request asynchronously continue when complete 
                client.GetAsync( "http://localhost:44331/DoCdssLoginTests?sAdName=bob.bob" ).ContinueWith(
                    ( requestTask ) =>
                    {
                        // Get HTTP response from completed task. 
                        HttpResponseMessage response = requestTask.Result;

                        // Check that response was successful or throw exception 
                        response.EnsureSuccessStatusCode();

                        // Read response asynchronously as JsonValue
                        response.Content.ReadAsStringAsync().ContinueWith(
                            ( readTask ) =>
                            {
                                var result = readTask.Result;
                                //Do something with the result
                                TextBox1.Text = result.ToString();
                                Button1.Text = result.ToString();
                            } );
                    } );
            }
            catch ( Exception ex )
            {
                TextBox1.Text = ex.Message;
                throw;
            }

Can anyone see what I'm doing wrong? I tried updating the text on the button too, but it also looks like it got changed and is unaltered on the page refresh.

Okay I figured it out.

Vadims comment about ContinueWith running in its own thread was the key.

I pulled the AsynchHelper from this post:

https://stackoverflow.com/questions/9343594/how-to-call-asynchronous-method-from-synchronous-method-in-c

and added it to the class.

and then changed the method thusly:

    protected void Button1_Click( object sender, EventArgs e )
    {
        try
        {
            string buffer = string.Empty;
            // Create an HttpClient instance 
            HttpClient client = new HttpClient();

            var result = AsyncHelper.RunSync<string>( () => client.GetStringAsync( "http://localhost:44331/DoCdssLoginTests?sAdName=bob.bob" ) );
            
            TextBox1.Text = result;

        }
        catch ( Exception ex )
        {
            TextBox1.Text = ex.Message;
            throw;
        }

        
    }

internal static class AsyncHelper
        {
            private static readonly TaskFactory _myTaskFactory = new
                TaskFactory( CancellationToken.None,
                    TaskCreationOptions.None,
                    TaskContinuationOptions.None,
                    TaskScheduler.Default );

            public static TResult RunSync<TResult>( Func<Task<TResult>> func )
            {
                return AsyncHelper._myTaskFactory
                    .StartNew<Task<TResult>>( func )
                    .Unwrap<TResult>()
                    .GetAwaiter()
                    .GetResult();
            }

            public static void RunSync( Func<Task> func )
            {
                AsyncHelper._myTaskFactory
                    .StartNew<Task>( func )
                    .Unwrap()
                    .GetAwaiter()
                    .GetResult();
            }
        }

This eliminated the cross thread updating (which is know to be an issue) and simplified away the asynch call in a synchronous method.

Now it's working as expected.