s&box Component Lifecycle: Exact Execution Order and Internal Guards

s&box Component Lifecycle: Exact Execution Order and Internal Guards

Derived directly from Component.cs and Component.Update.cs in the s&box engine source.

Execution Order

1. OnAwake() — Called once when the Component is first initialized. Runs inside GameTransform.DisableInterpolation() scope, so Transform changes here won't be interpolated.
2. OnEnabled() — Called after OnAwake or whenever the component transitions from disabled → enabled. Also runs inside DisableInterpolation().
3. OnStart() — Called once before the first OnUpdate(). Deferred until the first update tick after the component becomes active. Also runs inside DisableInterpolation().
4. OnUpdate() — Called every frame while enabled.
5. OnFixedUpdate() — Called at a fixed interval (physics tick rate). Time.Delta is the fixed interval here.
6. OnPreRender() — Called before rendering. Not called on dedicated servers (Application.IsHeadless).
7. OnDisabled() — Called when the component transitions from enabled → disabled.
8. OnDestroy() — Called once when the component is destroyed.

Key Internal Guards

• OnStart() is only called once (_startCalled flag). It fires from inside InternalUpdate() or InternalFixedUpdate(), meaning it can fire from either context.
• OnEnabled() and OnDisabled() are guarded by _onEnabled flag — they will never double-fire.
• Components on a PrefabCacheScene never execute (ShouldExecute returns false).
• Components marked DontExecuteOnServer won't execute on dedicated servers.
• Components that are not ExecuteInEditor won't execute in editor scenes.
• OnValidate() is called after deserialization and on property changes in the editor.
• OnRefresh() is called after a Component is refreshed from a network snapshot.

Callback Batching

Lifecycle callbacks (OnAwake, OnEnabled, OnDisabled, OnDestroy, OnValidate) are queued via CallbackBatch rather than called immediately. This prevents re-entrant issues during scene loading or destruction.

Action-Based Callbacks

Components expose action properties for use in ActionGraph / no-code contexts:

• OnComponentEnabled, OnComponentDisabled, OnComponentDestroy
• OnComponentStart, OnComponentUpdate, OnComponentFixedUpdate

Setting OnComponentUpdate or OnComponentFixedUpdate to a non-null value registers the component in the scene's update set even if it doesn't implement IUpdateSubscriber.