unity-scripting

Unity C# Scripting

Script Fundamentals

C# scripts (.cs files) are stored in the Assets folder. Scripts gain Unity functionality by inheriting from built-in types:

• UnityEngine.Object -- Makes custom types assignable to Inspector fields
• MonoBehaviour -- Attaches to GameObjects as components to control behavior in a scene
• ScriptableObject -- Standalone data assets not attached to GameObjects

Scripts operate in two contexts:

• Runtime scripts -- Execute in the Player build (use UnityEngine namespace)
• Editor scripts -- Run only in the Editor (use UnityEditor namespace, place in Editor folders)

MonoBehaviour Lifecycle

MonoBehaviours always exist as a Component of a GameObject. The lifecycle event functions execute in a strict order. You cannot rely on the order in which the same event function is invoked for different GameObjects unless configured via Script Execution Order settings.

Execution Order (ASCII Diagram)

INITIALIZATION
  |
  v
[Awake] ---------> Called when script instance loads (once per lifetime)
  |
  v
[OnEnable] ------> Called when object/component becomes enabled
  |
  v
(SceneManager.sceneLoaded fires here -- after OnEnable, before Start)
  |
  v
[Start] ---------> Called before first frame Update (once per lifetime)
  |
  |
  |  +===========================================+
  |  |          PHYSICS LOOP (fixed timestep)    |
  |  |                                           |
  +->| [FixedUpdate] --> Internal Physics ------>|
  |  |       |                                   |
  |  | [yield WaitForFixedUpdate resumes]        |
  |  +===========================================+
  |
  v
[Update] --------> Called once per frame
  |
  v
[yield null / yield WaitForSeconds resumes]
  |
  v
(Internal Animation Update)
  |   [OnAnimatorMove]
  |   [OnAnimatorIK]
  |
  v
[LateUpdate] ----> Called after all Update functions complete
  |
  v
RENDERING
  | [OnWillRenderObject]
  | [OnPreCull] [OnBecameVisible/Invisible]
  | [OnPreRender]
  | [OnRenderObject]
  | [OnPostRender]
  | [OnRenderImage]
  |
  v
[OnGUI] ---------> Called for GUI rendering events
  |
  v
[yield WaitForEndOfFrame resumes]
  |
  v
DEACTIVATION / TEARDOWN
  |
  v
[OnDisable] -----> Called when component/object is disabled
  |
  v
[OnDestroy] -----> Called before object destruction