MonoBehaviour lifecycle in Unity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output order of these MonoBehaviour methods?

Consider a Unity script attached to an active GameObject. Which sequence of method calls will Unity invoke first when the scene starts?

Unity

using UnityEngine;

public class TestLifecycle : MonoBehaviour
{
    void Awake() { Debug.Log("Awake"); }
    void Start() { Debug.Log("Start"); }
    void OnEnable() { Debug.Log("OnEnable"); }
}

A Start, Awake, OnEnable

B OnEnable, Awake, Start

C Awake, OnEnable, Start

D Awake, Start, OnEnable

💡 Hint

Remember that Awake is called before OnEnable, and Start is called after both.

Unity calls Awake first when the script instance is loaded, then OnEnable when the object becomes active, and finally Start before the first frame update.

❓ Predict Output

intermediate

What happens if you disable a GameObject during Update?

Given this script, what will be the output when the GameObject is active and Update disables it?

Unity

using UnityEngine;

public class DisableInUpdate : MonoBehaviour
{
    void Update()
    {
        Debug.Log("Update called");
        gameObject.SetActive(false);
    }

    void OnDisable()
    {
        Debug.Log("OnDisable called");
    }
}

A Only OnDisable called

B Update called\nOnDisable called

C Only Update called

D OnDisable called\nUpdate called

💡 Hint

Think about the order of method calls within the same frame.

Update runs first and logs "Update called". Then disabling the GameObject triggers OnDisable immediately, logging "OnDisable called".

🔧 Debug

advanced

Why does Start not get called when re-enabling a previously active GameObject?

Look at this script attached to a GameObject that starts active (so Start has already been called), is then disabled, and re-enabled at runtime. Why does Start not print "Start called" again?

Unity

using UnityEngine;

public class StartTest : MonoBehaviour
{
    void Start()
    {
        Debug.Log("Start called");
    }
}

// Elsewhere in code:
// gameObject.SetActive(false);
// gameObject.SetActive(true);

A Start is only called once when the script instance is first enabled, not every time the GameObject is enabled.

B Start is called only if Awake is called first, which is missing here.

C Start is called only if OnEnable is overridden in the script.

D Start is called only if the GameObject is enabled in the editor before play.

💡 Hint

Think about when Start is triggered in the lifecycle.

Start is called exactly once per MonoBehaviour instance, just before the first frame update the first time the script is enabled. Subsequent enables after disabling do not call Start again.

📝 Syntax

advanced

Which method signature is correct for OnDestroy in MonoBehaviour?

Choose the correct method signature for the OnDestroy callback in a MonoBehaviour script.

A void OnDestroy()

B void OnDestroy(bool isPermanent)

C public void OnDestroy()

D void OnDestroy(GameObject obj)

💡 Hint

Check the Unity documentation for OnDestroy method signature.

OnDestroy has no parameters and returns void. It is called when the MonoBehaviour will be destroyed.

🚀 Application

expert

How many times is FixedUpdate called per second if Time.fixedDeltaTime = 0.02?

In Unity, if Time.fixedDeltaTime is set to 0.02 seconds, how many times will FixedUpdate be called per second?

A 20 times

B Depends on frame rate

C 100 times

D 50 times

💡 Hint

Think about how fixedDeltaTime relates to FixedUpdate frequency.

FixedUpdate is called every fixedDeltaTime seconds. If fixedDeltaTime is 0.02, then 1 / 0.02 = 50 calls per second.