在Caliburn Micro中点击背景时，TextBox是否会失去焦点？

<Grid x:Name="BackgroundGrid" Background="White" cal:Message.Attach="[Event MouseLeftButtonDown] = [Action BackgroundClicked()]">
    <TextBox x:Name="MyTextBox" />
</Grid>

using Caliburn.Micro;

public class MyViewModel : Screen
{
    private readonly IEventAggregator _eventAggregator;

    public MyViewModel(IEventAggregator eventAggregator)
    {
        _eventAggregator = eventAggregator;
    }

    public void BackgroundClicked()
    {
        _eventAggregator.PublishOnUIThread(new BackgroundClickedEvent());
    }
}

public class BackgroundClickedEvent { }

using Caliburn.Micro;

public partial class App : Application
{
    private readonly IEventAggregator _eventAggregator = new EventAggregator();

    protected override void OnStartup(StartupEventArgs e)
    {
        base.OnStartup(e);

        var container = new SimpleContainer();
        container.Singleton<IEventAggregator>(_eventAggregator);
        container.Singleton<MyViewModel>();

        var bootstrapper = new Bootstrapper(container);
        bootstrapper.Initialize();
    }
}

public void BackgroundClicked()
{
    MyTextBox.FocusManager.FocusedElement = null;
}