public ItemViewer()
{
    InitializeComponent();
    Loaded += ItemViewer_Loaded;
}
 
void ItemViewer_Loaded(object sender, RoutedEventArgs e)
{
    if (LayoutRoot.Visibility != Visibility.Collapsed)
        throw new Exception("item.Visibility != Collapsed");
 
    var _TopFrom = this.RenderSize.Height;
    var _TopTo = 0;
    var _OpacityFrom = 0;
    var _OpacityTo = 1;
 
    ShowHide(LayoutRoot, null, _TopFrom, _TopTo, _OpacityFrom, _OpacityTo);
}
 
protected override void OnBackKeyPress(System.ComponentModel.CancelEventArgs e)
{
    var _TopFrom = 0;
    var _TopTo = this.RenderSize.Height;
    var _OpacityFrom = 1;
    var _OpacityTo = 0;
 
    e.Cancel = true;
    base.OnBackKeyPress(e);
 
    ShowHide(LayoutRoot, () => { NavigationService.GoBack(); }, 
        _TopFrom, _TopTo, _OpacityFrom, _OpacityTo);
}
 
private static void ShowHide(UIElement item, Action callback, double topFrom,
    double topTo, double opacityFrom, double opacityTo)
{
    // setup
    var _Translate = new TranslateTransform
    {
        X = 0,
        Y = topFrom
    };
    item.RenderTransform = _Translate;
    item.Visibility = Visibility.Visible;
    item.Opacity = opacityFrom;
 
    // animate
    var _Storyboard = new Storyboard();
    var _Duration = TimeSpan.FromSeconds(.5);
 
    // opacity
    var _OpacityAnimate = new DoubleAnimation
    {
        To = opacityTo,
        Duration = _Duration,
    };
    _Storyboard.Children.Add(_OpacityAnimate);
    Storyboard.SetTarget(_OpacityAnimate, item);
    Storyboard.SetTargetProperty(_OpacityAnimate,
        new PropertyPath(UIElement.OpacityProperty));
 
    // translate (location)
    var _TranslateAnimate = new DoubleAnimation
    {
        To = topTo,
        Duration = _Duration,
        EasingFunction = new SineEase
        {
            EasingMode = EasingMode.EaseOut
        }
    };
    _Storyboard.Children.Add(_TranslateAnimate);
    Storyboard.SetTarget(_TranslateAnimate, _Translate);
    Storyboard.SetTargetProperty(_TranslateAnimate,
        new PropertyPath(TranslateTransform.YProperty));
 
    // finalize
    _TranslateAnimate.Completed += (s, arg) =>
    {
        if (callback != null)
            callback();
    };
    _Storyboard.Begin();
}