A ViewStack Component for Silverlight 2 with Transitions and Cache management

using System;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Ink;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;

namespace SilverlightApplication1.Utils.Transitions
{
    public class WipeTransition : TransitionBase
    {


        private TimeSpan time;
        private UserControl newPage;
        private UserControl oldPage;
   
        private Brush oldOpacityMaskBrush;
        public WipeTransition()
            :this(WipeDirection.LeftToRight)
        {
        }

        public WipeTransition(WipeDirection direction, TimeSpan duration)
        {
            time = duration;
            this.direction = direction;
        }
        public WipeTransition(WipeDirection direction)
            : this(direction, TimeSpan.FromSeconds(.5))
        { }


        private WipeDirection direction;
        public WipeDirection Direction
        {
            get { return direction; }
            set { direction = value; }
        }

        private double timeAsDouble;
        public Double Duration
        {
            get { return timeAsDouble; }
            set {
                timeAsDouble = value;
                time = TimeSpan.FromSeconds(timeAsDouble);
                }
        }


        public override void PerformTranstition(UserControl newPage, UserControl oldPage)
        {
           
            this.newPage = newPage;
            this.oldPage = oldPage;
            if (newPage == null) return;

            
            Storyboard sb;
             
            GradientStopCollection gradientStopCollection = new GradientStopCollection();
            GradientStop gradientStop1 = new GradientStop();
            gradientStop1.Color = Colors.Black;
            gradientStop1.Offset = 0;

            GradientStop gradientStop2 = new GradientStop();
            gradientStop2.Color = Colors.Transparent;
            gradientStop2.Offset = 0;

            LinearGradientBrush linearGradientBrush = new LinearGradientBrush(gradientStopCollection, 0);
          

            switch (direction)
            {
                case WipeDirection.LeftToRight:
                    linearGradientBrush.StartPoint = new Point(0, 0);
                    linearGradientBrush.EndPoint = new Point(1, 0);
                    break;
                case WipeDirection.RightToLeft:
                    linearGradientBrush.StartPoint = new Point(1, 0);
                    linearGradientBrush.EndPoint = new Point(0, 0);
                    break;
                case WipeDirection.TopToBottom:
                    linearGradientBrush.StartPoint = new Point(0, 0);
                    linearGradientBrush.EndPoint = new Point(0, 1);
                    break;
                case WipeDirection.BottomToTop:
                    linearGradientBrush.StartPoint = new Point(0, 1);
                    linearGradientBrush.EndPoint = new Point(0, 0);
                    break;
            }



            gradientStopCollection.Add(gradientStop1);
            gradientStopCollection.Add(gradientStop2);

            oldOpacityMaskBrush = newPage.OpacityMask;
            newPage.OpacityMask = linearGradientBrush;
            
            Duration duration = new Duration(time);

            DoubleAnimation animation = new DoubleAnimation();
            animation.From = 0;
            animation.To =1.1;
            animation.By = 1;
            animation.Duration = duration;


            DoubleAnimation animation1 = new DoubleAnimation();
            animation1.From = 0;
            animation1.To = 1.1;
            animation1.By = 1;
            animation1.Duration = duration;


            sb = new Storyboard();
            sb.Duration = duration;
            sb.Children.Add(animation);
            sb.Children.Add(animation1);
            sb.Completed += sb_Completed;

            Storyboard.SetTarget(animation, gradientStop1);
            Storyboard.SetTargetProperty(animation, new PropertyPath("OffSet"));

            Storyboard.SetTarget(animation1, gradientStop2);
            Storyboard.SetTargetProperty(animation1, new PropertyPath("OffSet"));
            
            sb.Begin();

        }

        void sb_Completed(object sender, EventArgs e)
        {
            newPage.OpacityMask = oldOpacityMaskBrush;
            OnTransitionCompleted(newPage, oldPage);
        }

        public enum WipeDirection
        {
            LeftToRight,
            RightToLeft,
            TopToBottom,
            BottomToTop
        }
    }
}