unity-csharp-scripting

Unity C# Scripting Patterns

Overview

Core C# scripting reference for Unity development. Covers MonoBehaviour lifecycle, physics and collision APIs, animation scripting, audio, navigation, common design patterns, serialization, and ECS/DOTS coding patterns.

MonoBehaviour Lifecycle

Execution Order

Awake() -> OnEnable() -> Start() -> FixedUpdate() -> Update() -> LateUpdate() -> OnDisable() -> OnDestroy()

Method	When Called	Use For
Awake()	Once, when object instantiates (before Start)	Self-initialization, caching references
OnEnable()	Each time object becomes active	Subscribe to events, reset state
Start()	Once, before first Update (after all Awake)	Cross-object initialization
FixedUpdate()	Fixed timestep (default 0.02s)	Physics, Rigidbody movement
Update()	Every frame	Input, non-physics logic
LateUpdate()	After all Update calls	Camera follow, post-movement adjustments
OnDisable()	When object deactivates	Unsubscribe events, save state
OnDestroy()	When object is destroyed	Final cleanup, resource release

Key Rules

• Awake runs even on disabled components (but not disabled GameObjects)
• Never rely on Awake/Start order between scripts -- use [DefaultExecutionOrder(N)] or Script Execution Order settings
• Use OnValidate() for editor-time validation of serialized fields

Coroutines and Async

Coroutines

IEnumerator SpawnWaves(int count, float delay)
{
    for (int i = 0; i < count; i++)
    {
        SpawnEnemy();
        yield return new WaitForSeconds(delay);
    }
}
// Start: Coroutine handle = StartCoroutine(SpawnWaves(5, 1f));
// Stop: StopCoroutine(handle); or StopAllCoroutines();

Yield Instruction	Behavior
yield return null	Wait one frame
yield return new WaitForSeconds(t)	Wait t seconds (affected by timeScale)
yield return new WaitForSecondsRealtime(t)	Unscaled time
yield return new WaitForFixedUpdate()	Wait for next FixedUpdate
yield return new WaitForEndOfFrame()	After rendering
yield return new WaitUntil(() => condition)	Wait until predicate is true
yield return StartCoroutine(other)	Wait for nested coroutine

Async/Await (Unity 6+ / UniTask)

For Unity 2023+/Unity 6, Awaitable is built-in. For older versions, use UniTask.

async Awaitable LoadLevelAsync(string sceneName)
{
    await Awaitable.WaitForSecondsAsync(1f);
    var op = SceneManager.LoadSceneAsync(sceneName);
    while (!op.isDone)
    {
        progressBar.value = op.progress;
        await Awaitable.NextFrameAsync();
    }
}

Events and Delegates

Event Pattern (Recommended)

// Publisher
public class Health : MonoBehaviour
{
    public event System.Action<float> OnDamaged;  // event keyword prevents external invocation
    public event System.Action OnDeath;

    public void TakeDamage(float amount)
    {
        currentHealth -= amount;
        OnDamaged?.Invoke(amount);
        if (currentHealth <= 0) OnDeath?.Invoke();
    }
}

// Subscriber
void OnEnable() => health.OnDamaged += HandleDamage;
void OnDisable() => health.OnDamaged -= HandleDamage;
void HandleDamage(float amount) => /* react */;

ScriptableObject Event Channels

Decouple systems without direct references. Create GameEvent as a ScriptableObject asset, invoke from publishers, and listen from subscribers via GameEventListener MonoBehaviours. See references/design-patterns.md for full implementation.

Physics API Quick Reference

Rigidbody Movement (3D)

Task	Method	Where
Continuous force	rb.AddForce(dir * force)	FixedUpdate
Instant impulse	rb.AddForce(dir * force, ForceMode.Impulse)	FixedUpdate
Direct velocity	rb.linearVelocity = dir * speed	FixedUpdate
Kinematic move	rb.MovePosition(target)	FixedUpdate
Rotation	rb.MoveRotation(targetRot)	FixedUpdate

Note: In Unity 6, Rigidbody.velocity is renamed to Rigidbody.linearVelocity.

Raycasting

if (Physics.Raycast(origin, direction, out RaycastHit hit, maxDistance, layerMask))
{
    Debug.Log($"Hit {hit.collider.name} at {hit.point}");
}
// Use Physics.RaycastAll or Physics.RaycastNonAlloc for multiple hits
// 2D: Physics2D.Raycast, Physics2D.OverlapCircle, etc.

Collision vs Trigger

Callback	Requires	Use For
OnCollisionEnter/Stay/Exit	Both have colliders, at least one Rigidbody, isTrigger=false	Physical impacts
OnTriggerEnter/Stay/Exit	One collider has isTrigger=true, at least one Rigidbody	Zones, pickups, detection

Always use CompareTag("Enemy") instead of other.tag == "Enemy" (avoids GC allocation).

Animation Scripting

[RequireComponent(typeof(Animator))]
public class CharacterAnimation : MonoBehaviour
{
    static readonly int SpeedHash = Animator.StringToHash("Speed");
    static readonly int JumpTrigger = Animator.StringToHash("Jump");
    Animator _anim;

    void Awake() => _anim = GetComponent<Animator>();
    void Update()
    {
        _anim.SetFloat(SpeedHash, moveSpeed);
        if (jumped) _anim.SetTrigger(JumpTrigger);
    }
}

Cache Animator.StringToHash results as static readonly fields to avoid per-frame hashing. Use Animation Events for gameplay-timed callbacks (footsteps, hit frames). For IK, implement OnAnimatorIK(int layerIndex) with SetIKPosition/Rotation/Weight.

Audio Quick Reference

[RequireComponent(typeof(AudioSource))]
public class SFXPlayer : MonoBehaviour
{
    [SerializeField] AudioClip[] clips;
    AudioSource _source;
    void Awake() => _source = GetComponent<AudioSource>();
    public void PlayRandom() => _source.PlayOneShot(clips[Random.Range(0, clips.Length)]);
}

Use AudioSource.PlayOneShot() for overlapping SFX. Use AudioMixer with exposed parameters for volume control. Use snapshots for state transitions (combat vs. exploration).

Serialization

Type	Serialized	Notes
public fields	Yes	Visible in Inspector
[SerializeField] private	Yes	Preferred -- maintains encapsulation
[HideInInspector] public	Yes, hidden	Serialized but not shown
[NonSerialized] public	No	Opt-out of serialization
Properties	No	Never serialized by Unity
Dictionaries	No	Use serialized list + rebuild, or Odin/SerializedDictionary
Interfaces	No	Use abstract ScriptableObject or SerializeReference

Use [SerializeReference] for polymorphic serialization of interfaces and abstract types.

Common Design Patterns

Pattern	When to Use	Approach
Singleton	Global managers (Audio, GameState)	ScriptableObject-based or lazy MonoBehaviour
Observer	Decoupled communication	C# events or SO event channels
Command	Input/undo systems	Command interface + history stack
State Machine	AI, player states	Enum + switch, or class-based states
Object Pool	Bullets, particles, enemies	Queue with pre-instantiation
Service Locator	Testable global access	Static registry with interface keys

For detailed implementations and code examples, see references/design-patterns.md.

ECS/DOTS Quick Reference

Concept	Role
Entity	Lightweight ID (no MonoBehaviour)
IComponentData	Pure data struct on entities
SystemBase / ISystem	Logic operating on component queries
EntityQuery	Filter entities by component sets
Jobs (IJobEntity)	Multithreaded systems
Burst Compiler	SIMD-optimized native code

For ECS architecture patterns and migration guidance, see references/design-patterns.md.

Additional Resources

Reference Files

• references/design-patterns.md -- Full implementations of singleton, observer, command, state machine, object pool, service locator, and ECS patterns
• references/physics-animation-audio.md -- Detailed physics setup (2D and 3D), advanced animation (blend trees, IK, root motion, Animation Rigging), and audio architecture