Working with the UI thread

In Chapter 3, The Windows App SDK for a WPF Developer, you already met the Dispatcher class. It's a special class provided by the XAML framework that you can use to dispatch a task on the UI thread. Since every WinUI application has a single UI thread, Dispatcher becomes especially important when you are executing some code on a background thread but then, at some point, you have to interact with a UI control. Without using the Dispatcher class, the operation would raise an exception, since you can't update the UI from a different thread than the UI one.

UWP exposes a Dispatcher class on every page, which belongs to the Windows.UI.Core.CoreDispatcher namespace. Here is an example of how to use it:

await Dispatcher.RunAsync(Windows.UI.Core.
  CoreDispatcherPriority.Normal, () =>
{
    txtHeader.Text = "This is a header";
});

Actions on the UI thread are dispatched using the RunAsync() method, which...