MonoBehaviour lifecycle in Unity - Step-by-Step Execution

Concept Flow - MonoBehaviour lifecycle

Game Start

↓

Awake() called

↓

OnEnable() called

↓

Start() called

↓

Update() called every frame

↓

FixedUpdate() called every physics step

↓

LateUpdate() called every frame after Update

↓

OnDisable() called

↓

OnDestroy() called

↓

Game End

This flow shows the order in which Unity calls MonoBehaviour lifecycle methods from game start to end.

Execution Sample

Unity

void Awake() { Debug.Log("Awake called"); }
void Start() { Debug.Log("Start called"); }
void Update() { Debug.Log("Update called"); }

This code logs messages when Awake, Start, and Update methods are called during the game lifecycle.

Execution Table

Step	Method Called	When Called	Action	Output
1	Awake()	When script instance is loaded	Initialize variables	Logs: Awake called
2	OnEnable()	When object becomes active	Prepare object	No output in sample
3	Start()	Before first frame update	Setup before gameplay	Logs: Start called
4	Update()	Every frame	Game logic update	Logs: Update called
5	FixedUpdate()	Every physics step	Physics calculations	No output in sample
6	LateUpdate()	Every frame after Update	Follow-up logic	No output in sample
7	OnDisable()	When object becomes inactive	Cleanup or pause	No output in sample
8	OnDestroy()	When object is destroyed	Final cleanup	No output in sample
9	End	Game ends or object destroyed	Stop lifecycle	No further calls

💡 Lifecycle ends when object is destroyed or game stops.

Variable Tracker

Variable	Start	After Awake	After OnEnable	After Start	After Update	After OnDisable	After OnDestroy
isActive	false	false	true	true	true	false	false
initialized	false	true	true	true	true	true	false

Key Moments - 3 Insights

Why is Awake called before Start?

Awake is called when the script instance loads to initialize variables early, while Start is called just before the first frame to set up gameplay. See execution_table rows 1 and 3.

Why does Update run many times but Awake only once?

Update runs every frame to keep game logic updated, but Awake runs only once to initialize. See execution_table rows 1 and 4.

What happens when the object is disabled?

OnDisable is called to pause or clean up before the object becomes inactive. See execution_table row 7 and variable_tracker for isActive changes.

Visual Quiz - 3 Questions

Look at the execution_table, at which step is the object considered active?

A Step 7 OnDisable()

B Step 2 OnEnable()

C Step 1 Awake()

D Step 8 OnDestroy()

💡 Hint

Check variable_tracker column After OnEnable where isActive changes to true.

According to the execution_table, which method runs every frame during gameplay?

A Start()

B Awake()

C Update()

D OnDisable()

💡 Hint

Look at Step 4 in execution_table where Update() is called every frame.

If the object is destroyed, which method is called last according to the lifecycle?

A OnDestroy()

B OnDisable()

C Start()

D Awake()

💡 Hint

See execution_table Step 8 for OnDestroy() called when object is destroyed.

Concept Snapshot

MonoBehaviour lifecycle methods run in this order:
Awake() -> OnEnable() -> Start() -> Update() (every frame) -> FixedUpdate() (physics) -> LateUpdate() -> OnDisable() -> OnDestroy()
Awake initializes early, Start runs before first frame, Update runs every frame.
OnDisable and OnDestroy handle cleanup.
This order controls script behavior during game play.

Full Transcript

The MonoBehaviour lifecycle in Unity starts with Awake, which initializes the script instance when loaded. Then OnEnable is called when the object becomes active. Start runs before the first frame update to prepare gameplay. Update runs every frame to handle game logic. FixedUpdate runs every physics step for physics calculations. LateUpdate runs after Update for follow-up logic. When the object is disabled, OnDisable is called to pause or clean up. Finally, OnDestroy is called when the object is destroyed for final cleanup. Variables like isActive track if the object is active, changing after OnEnable and OnDisable. This lifecycle ensures scripts run in the correct order during the game.