Coin Counter with Events

Question

In Unity, how can I send an event to a single game object? Or, how else can I solve this problem?

Scenario: Let's say there are six players in a scene. And a bunch of coins for them to collect.

Each coin has a CoinCollectable script. When it detects a collision with a player, it invokes its OnCollected event.

public class CoinCollectable : MonoBehaviour
{
    // The action to invoke when this coin is collected by a player
    public static event Action<GameObject, int> OnCollected;

    // When a coin is touched
    private void OnTriggerEnter2D(Collider2D other) {

        // If not a player, abort
        if (!other.gameObject.CompareTag("Player")) return;

        // Invoke the coin collected event
        OnCollected?.Invoke(other.gameObject, coinValue);
    }
}

All players listen to this event in their PlayerCoinCounter script.

public class PlayerCoinCounter : MonoBehaviour
{
    private void OnEnable()
    {
        // Subscribe to events
        CoinCollectable.OnCollected += IncreaseCoins;
    }

    private void OnDisable()
    {
        // Un-subscribe from events
        CoinCollectable.OnCollected -= IncreaseCoins;
    }

    private void IncreaseCoins(GameObject player, int coinsToAdd)
    {
        // If this is not the player who collected the coin, abort
        if(player != this.gameObject) return;

        // (Increase the current coin counter value)       
    }
}

The problem is that with this setup, every single player has to check "Was I the one who collected the coin?" in their event handler method. This feels cumbersome and not very elegant.

How would you approach this problem? I wonder:

Is there a way to send the event just to the one player who actually collected the coin? (To avoid each player having to check if they collected it)
If not, then in OnTriggerEnter2D, should I instead do other.GameObject.GetComponent<PlayerCoinCounter>().IncreaseCoins(...)? This does not feel ideal, because I would be assuming that the player has such a component. So I would lose the decoupling that the event approach provides.

PS: I am using events to minimise coupling.

derHugo derHugo · Accepted Answer · 2021-06-27T14:07:43

The coin doesn't have to do anything. I would go the other way round:

Have this on your coin

public class Coin : MonoBehaviour
{
    public int value;
}

Then rather check on the player for collision with coins and increase its own counter.

Something like

public class PlayerCoinCounter : MonoBehaviour
{
    public int coins;

    private void OnTriggerEnter2D(Collider2D other) {

        // If not a player, abort
        if (!other.TryGetComponent<Coin>(out var coin)) return;

        coins += coin.value;
    }
}

No events needed at all.

If you have a "dependency" on a tag or a certain component makes little difference in my eyes.

But I would say the coins are not responsible for increasing the player points but rather the player itself ;)

Coin Counter with Events

2 Answers