Tạo một class có thể tự tạo instance.

using Microsoft.Xna.Framework.Content;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
namespace DemoRPG
{
    public class ScreenManager
    {
        private static ScreenManager instance;
        public static ScreenManager Instance
        {
            get
            {
                if (instance == null)
                    instance = new ScreenManager();
                return instance;
            }
        }
        public Vector2 Dismensions { private set; get; }
        public ScreenManager()
        {
            Dismensions = new Vector2(640, 480);
        }
        public void LoadContent(ContentManager content)
        { }
        public void UnloadContent()
        {

        }
        public void Update(GameTime gameTime)
        { }
        public void Draw(SpriteBatch spriteBatch)
        { }

    }
}