YnQuadTree in action with 50 sprites. This gist demonstrate you how it is simple to use a QuadTree structure in a game using Yna Engine. More information on the project page http://yna.codeplex.com

YnQuadTreeTest.cs

public class TestYnQuadTree
{
  private List<YnSprite> sprites;
	private YnSprite heroSprite;
	private YnQuadTree quadTree;
	
	public TestGame()
	{
		// Init some Sprites
		sprites = new List<YnSprite>();
		for (int i = 0; i < 50; i++)
		{
			// Create and init 50 Sprites
			YnSprite sprite = new YnSprite("SpriteAsset");
			sprite.Position = new Vector2(Math.Random() * YnG.Width, Math.Random() * YnG.Height);
			// Add the sprite to the scene
			Add(sprite);
			// Add the sprite to the collection of collidable objects
			sprites.Add(sprite);
		}
		
		// Init the player
		heroSprite = new Sprite("HeroAsset");
		heroSprite.Position = new Vector2(Math.Random() * YnG.Width, Math.Random() * YnG.Height);
		Add(heroSprite);
		
		// Init the QuadTree
		quadTree = new YnQuadTree(0, new Rectangle(0, 0, YnG.Width, YnG.Height));
		quadTree.MaxObjectsPerNode = 10;
	}

	public override void Update(GameTime gameTime)
	{
		base.Update(gameTime);
		
		 // Update the quadtree structure
		quadTree.Begin(spriteToCollide.ToArray());
		
		// Move your hero, do what you want ;)
		someUpdateLogic();
		
		// mSprite is the tested Sprite (you can use an array of ICollider2, so you can have a different object on mSprite parameter)
		// lSprite is the candidate that can be tested
		quadTree.Test(heroSprite, (mSprite, lSprite) =>
			{
				// If collide the heroSprite take its last position
				if (heroSprite.Rectangle.Intersects(lSprite.Rectangle))
					heroSprite.Position = heroSprite.LastPosition;
			});
	}
}