public void AddScene(GameScene scene)
        {
            scene.SceneManager = this;
            scene.IsExiting = false;

            // If we have a graphics device, tell the scene to load content.
            if (isInitialized)
            {
                scene.LoadContent();
            }

            scenes.Add(scene);
        }
 public void RemoveScene(GameScene scene)
 {
     // If we have a graphics device, tell the scene to unload content.
     if (isInitialized)
     {
         scene.UnloadContent();
     }
     scenes.Remove(scene);
     scenesToUpdate.Remove(scene);
 }