Transition on MenuItem with YnTransition

MenuItem.cs

using System;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
using Yna;
using Yna.Display;
using Yna.Display.Effect;

namespace SpaceGame.States.Menu
{

    public class MenuItem : YnGroup
    {
        public const int ItemWidth = 350;
        public const int ItemHeight = 75;
        public const int BorderSize = 5;
        private static Color BackgroundColor = Color.White;
        private static Color ForegroundColor = new Color(0, 108, 165);

        private YnSprite _foreground;
        private YnSprite _background;
        private YnText _contentText;
        private bool _selected;
        private int _itemPosition;

        // Transition
        private YnTransition _transition;

        public bool Selected
        {
            get { return _selected; }
            set { _selected = value; }
        }

        public int ItemPosition
        {
            get { return _itemPosition; }
        }

        public void SetSelected(bool selected)
        {
            _selected = selected;

            if (_selected)
            {
                _contentText.Color = Color.AntiqueWhite;

                _transition.StartTransitionOn();
            }
            else
            {
                _contentText.Color = Color.White;

                _transition.StartTransitionOff();
            }
        }

        public MenuItem(string text, int x, int y, int position, bool selected = false)
        {
            _itemPosition = position;
            _selected = selected;

            Rectangle = new Rectangle(x, y, ItemWidth, ItemHeight);

            _background = new YnSprite(Rectangle, BackgroundColor);
            _background.Alpha = 0.0f;
            //_background.Visible = false;
            Add(_background);

            _foreground = new YnSprite(new Rectangle(x, y, ItemWidth - BorderSize, ItemHeight - BorderSize), ForegroundColor);
            Add(_foreground);

            _contentText = new YnText("Fonts/Menu", Vector2.Zero, text);
            _contentText.Color = Color.White;
            Add(_contentText);

            _transition = new YnTransition(350.0f, 250.0f);
        }

        public override void Initialize()
        {
            base.Initialize();

            _foreground.Position = new Vector2(
                (int)(_background.X + _background.Width / 2 - _foreground.Width / 2),
                (int)(_background.Y + _background.Height / 2 - _foreground.Height / 2));

            CenterText();
        }

        private void CenterText()
        {
            _contentText.Position = new Vector2(
                (_background.X + _background.Width / 2) - _contentText.ScaledWidth / 2,
                (_background.Y + _background.Height / 2) - _contentText.ScaledHeight / 2);
        }

        public override void Update(GameTime gameTime)
        {
            base.Update(gameTime);

            // Mise à jour de la transition
            _transition.Update(gameTime);

            if (_transition.TransitionState == TransitionState.TransitionOn)
                _background.Alpha = _transition.Alpha;

            else if (_transition.TransitionState == TransitionState.TransitionOff)
                _background.Alpha = _transition.Alpha;
        }
    }
}