I have tried this (found here on Stackoverflow)

Asynchronous implementation of an event handler (Yes, that's all):

     private async void Button_Clicked(object sender, EventArgs e)
     {
         var progress = new Progress<string>(s => label.Text = s);
         await Task.Factory.StartNew(() => SecondThreadConcern.LongWork(progress),
                                     TaskCreationOptions.LongRunning);
         label.Text = "completed";
     }

Implementation of the second thread that notifies the UI thread:

     class SecondThreadConcern
     {
         public static void LongWork(IProgress<string> progress)
         {
             // Perform a long running work...
             for (var i = 0; i < 10; i++)
             {
                 Task.Delay(500).Wait();
                 progress.Report(i.ToString());
             }
         }
     }

It does update the GUI, but only after LongWork returns.
How do I get label.Text to update when the for loop is running?