Content.Resized Event

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 });
}