private void Animation_Completed(object sender, EventArgs e)
        {
            switch (navArgs.NavigationMode)
            {
            case NavigationMode.New:
                if (navArgs.Uri == null)
                {
                    NavigationFrame.Navigate(navArgs.Content);
                }
                else
                {
                    NavigationFrame.Navigate(navArgs.Uri);
                }
                break;

            case NavigationMode.Back:
                NavigationFrame.GoBack();
                break;

            case NavigationMode.Forward:
                NavigationFrame.GoForward();
                break;

            case NavigationMode.Refresh:
                NavigationFrame.Refresh();
                break;
            }
            inNavigation = false;

            var animation = new DoubleAnimation
            {
                From     = 0f,
                To       = 1f,
                Duration = new Duration(TimeSpan.FromMilliseconds(200))
            };

            NavigationFrame.BeginAnimation(OpacityProperty, animation);
        }