Private WithEvents rootPage As Page = New Page()
Private WithEvents htmlContent As Content
Private Sub Application_Startup(ByVal o As Object, ByVal e As StartupEventArgs) Handles Me.Startup
    Me.RootVisual = rootPage
    htmlContent = Me.Host.Content
End Sub

Private Sub ToggleFullScreen(ByVal sender As Object, _
    ByVal e As MouseButtonEventArgs) Handles rootPage.MouseLeftButtonDown
    Me.Host.Content.IsFullScreen = Not Me.Host.Content.IsFullScreen
End Sub

Private Sub DisplaySizeInformation( _
    ByVal sender As Object, ByVal e As EventArgs) _
    Handles htmlContent.FullScreenChanged, htmlContent.Resized

    Dim message As String = String.Format( _
        "ActualWidth={0}, ActualHeight={1}", _
        Me.Host.Content.ActualWidth, _
        Me.Host.Content.ActualHeight)

    rootPage.LayoutRoot.Children.Clear()
    Dim t As New TextBlock()
    t.Text = message
    rootPage.LayoutRoot.Children.Add(t)

End Sub

Page rootPage = new Page();
private void Application_Startup(object sender, StartupEventArgs e)
{
    this.RootVisual = rootPage;

    rootPage.LayoutRoot.MouseLeftButtonDown +=
        delegate(Object s, MouseButtonEventArgs args) {
            this.Host.Content.IsFullScreen =
                !this.Host.Content.IsFullScreen;
        };

    this.Host.Content.FullScreenChanged += 
        new EventHandler(DisplaySizeInformation);

    this.Host.Content.Resized += 
        new EventHandler(DisplaySizeInformation);
}

private void DisplaySizeInformation(Object sender, EventArgs e)
{
    String message = String.Format(
        "ActualWidth={0}, ActualHeight={1}",
        this.Host.Content.ActualWidth,
        this.Host.Content.ActualHeight);

    rootPage.LayoutRoot.Children.Clear();
    rootPage.LayoutRoot.Children.Add(
        new TextBlock { Text = message });
}