public class OverlappingAppBarBehavior: Behavior<PhoneApplicationPage>
{
    private static readonly double _appBarOffset = 74.0;
    private static readonly double _reducedAppBarOffset = 70.0;
    private static readonly double _appBarOpacity = 0.99;

    private static readonly IDictionary<PageOrientation, Thickness> _pageMargins = new Dictionary<PageOrientation, Thickness>
    {
        {PageOrientation.PortraitUp, new Thickness(0.0, 0.0, 0.0, _appBarOffset)},
        {PageOrientation.PortraitDown, new Thickness(0.0, _appBarOffset, 0.0, 0.0)},
        {PageOrientation.LandscapeLeft, new Thickness(0.0, 0.0, _reducedAppBarOffset, 0.0)},
        {PageOrientation.LandscapeRight, new Thickness(_appBarOffset, 0.0, 0.0, 0.0)}
    };

    protected override void OnAttached()
    {
        AssociatedObject.Loaded += OnLoaded;
        AssociatedObject.OrientationChanged += OnOrientationChanged;
    }

    private void OnLoaded(object sender, RoutedEventArgs e)
    {
        AssociatedObject.Loaded -= OnLoaded;
        UpdateAppBarState();
    }

    private void OnOrientationChanged(object sender, OrientationChangedEventArgs e)
    {
        UpdateAppBarState();
    }

    private void UpdateAppBarState()
    {
        var appBar = AssociatedObject.ApplicationBar;
         
        if (appBar == null)
        {
            return;
        }

        appBar.Opacity = _appBarOpacity;

        var content = AssociatedObject.Content as FrameworkElement;
        if (content == null)
        {
            return;
        }

        Thickness margin;
        AssociatedObject.Margin = _pageMargins.TryGetValue(AssociatedObject.Orientation, out margin)
            ? margin
            : new Thickness(0);
    }
}