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OnEnable() and OnDisable() track a Unity component’s active and enabled state; they are not one-time setup and final-cleanup callbacks. Use them for work that begins and ends with an active period, and make that work safe to repeat. The five mistakes below cover the lifecycle assumptions most likely to cause bugs.
1. Treating OnEnable() as a one-time initializer
OnEnable() runs when an enabled component becomes active, including when its GameObject or an inactive parent becomes active. It can run again after the component or GameObject is disabled and later re-enabled. Unity documents that, on entering Play Mode, it runs after Awake() and before Start() on the same object. Unity’s Unity 6.0.7 reference describes these invocation cases.
That makes OnEnable() a poor home for work that must happen only once, such as allocating a resource that should persist across disable cycles or resetting state that should survive them. Put one-time setup in the appropriate initialization path, and reserve OnEnable() for work needed for each active period. Choose based on when the component’s required data is available and whether it must be safe while inactive.
2. Assuming another object’s initialization has already run
The ordering guarantee between Awake() and OnEnable() applies to the same object. It does not mean every object’s Awake() runs before every other object’s OnEnable(). Unity’s event-function execution-order manual says that ordering across multiple GameObjects is not deterministic unless explicitly documented or settable.
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If a component needs another system to be ready, do not rely on callback names or an observed scene-load order. Instead, use a serialized reference where appropriate, or introduce an explicit initialization or coordination step. Also account for runtime-instantiated objects: scene-load ordering statements do not automatically establish every ordering relationship for objects created later.
3. Subscribing to events without a matching unsubscribe
If a component should receive notifications only while active, subscribe in OnEnable() and remove that subscription in OnDisable(). Unity does not automatically manage custom event subscriptions. A publisher can continue invoking a registered listener after that listener becomes inactive, depending on the event mechanism.
Use the same publisher and delegate in both paths, and check repeated enable-disable cycles for duplicate registrations. A useful design test is whether the listener should still receive the event while disabled: if yes, its subscription belongs elsewhere; if no, pair registration and removal with the active period.
4. Treating OnDisable() as final destruction
OnDisable() is called in more situations than deliberately unchecking a component. Unity’s Unity 6.0.3 reference lists component disabling, parent GameObject deactivation, destruction of the component or parent, scene unloading, and script reload as part of a domain reload. See the documented cases.
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5. Making activation work unsafe to repeat
Even correctly placed callbacks can cause trouble if they assume they run only once. A second activation might duplicate a subscription, start a routine again, reacquire a handle without releasing the old one, or reset state that should persist. These are design risks implied by repeatable active-state transitions, not special automatic behavior of Unity.
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Give each piece of activation work a clear ownership rule:
- Acquire or register on activation: obtain only what the active period needs.
- Release or unregister on deactivation: undo that active-period work using the matching operation.
- Keep persistent state separate: store data that must survive disable cycles outside reset logic that runs on every enable.
- Check repeated transitions: make sure enabling, disabling, and enabling again leaves one valid registration or resource, not duplicates or stale references.
These lifecycle descriptions reflect Unity’s documented behavior for Unity 6.0.7 OnEnable() and Unity 6.0.3 OnDisable(); check the documentation for the editor version used by your project when writing version-specific code.
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