The Calling Thread Must Be Sta, Because Many UI Components Require This in Wpf

WPF and background worker and the calling thread must be STA

There are numerous duplicates of this issue on Stack Overflow. For example, this question.

Bottom line - any time you create UI components, you must use a single-threaded apartment (STA) thread. Background workers are not STA. Therefore, you cannot create UI components in background workers. You cannot update UI components from background workers. Background workers are designed to run in the background (big surprise there), possibly to crunch data and return a result later on.

Why am i getting this error: The calling thread must be STA, because many UI components require this?

You get this exception because the Timer callback is executed in a thread pool thread that doesn't have ApartmentState.STA, which is required for creating WPF UI elements.

Better use the DispatcherTimer class, which has a Tick event that is fired in the UI thread.

Use it like shown below for a single shot action. If you actually intended to execute the Tick handler periodically, just remove the Stop() statement.

public MainWindow()
{
    InitializeComponent();

    var timer = new DispatcherTimer { Interval = TimeSpan.FromSeconds(5) };
    timer.Tick += ShowBallon;
    timer.Start();
}

private void ShowBallon(object sender, EventArgs e)
{
    ((DispatcherTimer)sender).Stop();

    string title = "WPF NotifyIcon";
    string text = "This is a standard balloon";
    new TaskbarIcon().ShowBalloonTip(title, text, BalloonIcon.None);
}

Task.Delay(N) System.InvalidOperationException: 'The calling thread must be STA, because many UI components require this.'

You can pass your own synchronization context to ContinueWith to tell the task scheduler where your continuation should run:

await Task.Delay(2000).ContinueWith(_ =>
                {
                    Restart wndRestart = new Restart();
                    wndRestart.Show();
                },
                TaskScheduler.FromCurrentSynchronizationContext()
            );

Otherwise you'll get a thread-pool thread that most likely isn't STA.

However, for a one-shot in WPF to perform some action after a delay, it's perfectly fine to just use a DispatcherTimer as well.

Why leaps exception: The calling thread must be STA, because many UI components require this?

Do not create Image controls in your view model, especially not when you load images asynchronously.

Change your view model to have an ObservableCollection of ImageSource:

public ObservableCollection<ImageSource> Images { get; set; }
    = new ObservableCollection<ImageSource>();

Then in your load method make sure that adding images to the collection is done in the UI thread. To make the BitmapImages cross-thread accessible, you also have to freeze them:

var bitmap = new BitmapImage(new Uri(fileInfo.FullName));
bitmap.Freeze();

Application.Current.Dispatcher.BeginInvoke(new Action(() => Images.Add(bitmap)));

Finally display the images by means of an ItemsControl with an appropriate ItemTemplate:

<ItemsControl ItemsSource="{Binding Images}">
    <ItemsControl.ItemTemplate>
        <DataTemplate>
            <Image Source="{Binding}"/>
        </DataTemplate>
    </ItemsControl.ItemTemplate>
</ItemsControl>

---

That said, you may also replace the ObservableCollection<ImageSource> by an ObservableCollection<string>, which would hold the image file paths. This is possible because WPF provides built-in conversion from string (and Uri) to ImageSource. Consequently, you would then also not need any asynchronous task anymore.

---

Related Topics