WinForm: Async/wait vs raw worker thread regarding updating UI control on UI thread

1. Async/await

await Task.Delay(5000);
statusLabel.Text = "Work Completed!";

This won’t throw exception because

• When we await, the method pauses, but the UI thread is free to process events.
• After the await, the continuation automatically resumes on the original calling thread, which in a WinForms/WPF app is the UI thread.
• That’s why we can update UI controls directly

2. Raw worker thread

Thread worker = new Thread(() =>
{
    Thread.Sleep(5000);
    statusLabel.Text = "Work Completed!"; //❌
});
worker.Start();

• The worker thread runs completely separate from the UI thread.
• Attempting to update a control directly causes an exception.
• We must marshal the call to the UI thread:

statusLabel.Invoke(new Action(() =>
{
    statusLabel.Text = "Work Completed!";
}));

So this is just to show the advantage of using asynchronous programming with async/await/Task which was introduced in 2012 alongside .NET Framework 4.5.

Before .Net Framework 4.5 we have to do the nasty thing you see with Invoke.