Group Listening

public class DeckController : MonoBehaviour {
	public GameObject back;
	public TextMeshPro cardCounter;
	private Contexts _contexts;
	private IGroup<GameEntity> _deckGroup;

	private void Awake() {
		_contexts = Contexts.sharedInstance;
		_deckGroup = _contexts.game.GetGroup(GameMatcher.AllOf(GameMatcher.Card, GameMatcher.InDeck));
		_deckGroup.OnEntityAdded += UpdateCounter;
		_deckGroup.OnEntityRemoved += UpdateCounter;
		//_deckGroup.OnEntityAdded
	}

	private void UpdateCounter(IGroup<GameEntity> @group, GameEntity entity, int index, IComponent component) {
		cardCounter.text = group.count.ToString();
		back.SetActive(group.count != 0);
	}

	private void OnDestroy() {
		_deckGroup.OnEntityAdded -= UpdateCounter;
		_deckGroup.OnEntityRemoved-= UpdateCounter;
	}
}