unity-pattern-observer

name	unity-pattern-observer
description	Observer
category	unity
source	unity-design-patterns-skills
source_path	patterns/observer/SKILL.md

Observer

Purpose

Notify multiple listeners when state changes while keeping the source independent from the listeners.

Use When

• UI, audio, and achievements react to the same source data.
• One source should fan out to multiple subscribers.
• Loose coupling matters more than strict call order.

Avoid When

• Execution order is critical.
• One direct call is simpler and enough.

Unity Implementation Recipe

1. Define explicit event payloads.
2. Subscribe and unsubscribe with lifecycle hooks.
3. Separate ongoing state change events from one-shot events.
4. Test unload and no-listener cases.

Common Pitfalls

• Forgetting to unsubscribe.
• Broadcasting vague events that force listeners to re-query everything.

Minimal Unity Sketch

public sealed class PlayerHealth
{
    public event Action<int, int>? Changed;
    private int _current = 100;
    private int _max = 100;

    public void TakeDamage(int damage)
    {
        _current = Math.Max(0, _current - damage);
        Changed?.Invoke(_current, _max);
    }
}

Response Shape

• Say whether Observer is actually the right fit.
• Map it to concrete Unity types, ownership, and lifecycle.
• Prefer a production-shaped skeleton over a long tutorial dump.
• Call out the simpler alternative if this pattern would be overengineering.