unity-core
Unity core scripting fundamentals — MonoBehaviour lifecycle, GameObject / Component model, ScriptableObjects, prefabs, serialization, coroutines, events, and execution order. USE WHEN: writing or refactoring core Unity scripts, designing data flow, setting up ScriptableObjects, dealing with serialization issues, choosing between Update / FixedUpdate / LateUpdate, coroutine vs async patterns. DO NOT USE FOR: rendering / shaders (use `unity-rendering`); 2D-specific topics (use `unity-2d-*`); networking (use `unity-netcode`); ECS/DOTS (use `unity-dots`).
What this skill does
# Unity Core
## MonoBehaviour Lifecycle
```
Awake → once, per script instance, even if disabled
OnEnable → each time GameObject/component becomes active
Start → once, just before first Update, only if active
FixedUpdate → fixed timestep (default 0.02s); physics writes here
Update → every frame
LateUpdate → after all Update; camera follow, IK adjustments
OnDisable → when component/GO becomes inactive
OnDestroy → when component/GO is destroyed (or app quits)
```
Order across objects: `Awake`/`OnEnable` for ALL objects, then `Start` for ALL, then per-frame loops. Tweak per-script via Edit > Project Settings > Script Execution Order — sparingly.
## ScriptableObject — data assets
```csharp
[CreateAssetMenu(menuName = "Game/Weapon", fileName = "NewWeapon")]
public class WeaponData : ScriptableObject {
public string displayName;
[Min(0)] public int damage = 10;
[Range(0f, 5f)] public float fireRate = 0.5f;
public Sprite icon;
public AudioClip fireSfx;
}
```
Use them for: tuning data, configurable enemy stats, level definitions, event channels. Avoid them as runtime mutable singletons across scenes — values persist in editor between play sessions.
## Reference injection (no Find)
```csharp
public class Enemy : MonoBehaviour {
[SerializeField] private WeaponData weapon; // assigned in inspector
[SerializeField] private Transform target; // explicit dependency
private Rigidbody _rb; // cached own component
private void Awake() => _rb = GetComponent<Rigidbody>();
}
```
Never: `GameObject.Find`, `FindObjectOfType` in Update. Acceptable: once in Awake/Start when injection isn't possible (rare).
## Coroutines vs async
| Use case | Pick |
|----------|------|
| Wait one frame / WaitForSeconds / WaitForFixedUpdate | Coroutine — `IEnumerator` + `yield return` |
| HTTP / file IO / long async ops | `async UniTask` (UniTask package) or `async Task` with `WhenAll` |
| Cancellation / structured concurrency | UniTask + CancellationToken |
| Cross-platform WebGL | Coroutines (no real threads) or UniTask |
```csharp
private Coroutine _flashRoutine;
private IEnumerator FlashRoutine() {
var renderer = GetComponent<Renderer>();
var original = renderer.material.color;
for (int i = 0; i < 3; i++) {
renderer.material.color = Color.red;
yield return new WaitForSeconds(0.1f);
renderer.material.color = original;
yield return new WaitForSeconds(0.1f);
}
_flashRoutine = null;
}
public void Flash() {
if (_flashRoutine != null) StopCoroutine(_flashRoutine);
_flashRoutine = StartCoroutine(FlashRoutine());
}
```
## Events — UnityEvent vs C# event vs ScriptableObject channel
| Style | When |
|-------|------|
| `C# event Action<T>` | Internal cross-script communication, no inspector wiring |
| `UnityEvent<T>` | Inspector-bound callbacks; designer-friendly |
| ScriptableObject event channel | Decoupling across scenes / between systems with no direct reference |
## Serialization rules
- `[SerializeField] private` over `public` for inspector exposure.
- Lists/arrays of references serialize fine; cyclic references via `[SerializeReference]` only when needed (heavier).
- `Dictionary<TK,TV>` does NOT serialize — use parallel `List<TK>`+`List<TV>` or `SerializableDictionary` packages.
- For polymorphic data (e.g. behaviour trees), use `[SerializeReference]` + interfaces.
## Anti-patterns
| Anti-pattern | Fix |
|---|---|
| Logic on every Update | Throttle with `if (Time.frameCount % N == 0)` or events |
| `Camera.main` in Update | Cache once in Awake (`_mainCam = Camera.main;`) |
| `transform.position` writes inside FixedUpdate without Rigidbody | Use `rb.MovePosition`, never `transform.position` for physics objects |
| Singleton MonoBehaviour with `Instance` accessed before Awake | Move init to `Awake`; use `RuntimeInitializeOnLoadMethod` for boot logic |
| Public mutable fields | `[SerializeField] private` + property |
## Production checklist
- [ ] Asmdefs split runtime / editor / test
- [ ] No `Find*` calls in hot paths
- [ ] All physics writes in FixedUpdate
- [ ] ScriptableObjects used for tuning data
- [ ] String hashes cached for Animator parameters
- [ ] Events disposed in OnDisable / OnDestroy
- [ ] Coroutines stopped on disable to avoid orphan loops
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