DontDestroyOnLoad usage in Unity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output when using DontDestroyOnLoad?

Consider the following Unity C# script attached to a GameObject. What will be the output in the console after loading a new scene?

Unity

using UnityEngine;
using UnityEngine.SceneManagement;

public class TestDontDestroy : MonoBehaviour
{
    void Awake()
    {
        DontDestroyOnLoad(gameObject);
        Debug.Log("Object Awake");
    }

    void Start()
    {
        Debug.Log("Object Start");
        SceneManager.LoadScene("Scene2");
    }

    void OnEnable()
    {
        Debug.Log("Object Enabled");
    }
}

A "Object Awake\nObject Enabled\nObject Start" printed twice

B "Object Awake\nObject Enabled\nObject Start" printed once

C Only "Object Awake" printed once

D No output printed because scene loads immediately

💡 Hint

Think about what DontDestroyOnLoad does to the GameObject when a new scene loads.

DontDestroyOnLoad keeps the GameObject alive across scene loads, so Awake and Start run once. OnEnable runs once when the object is enabled. The logs appear once.

🧠 Conceptual

intermediate

What does DontDestroyOnLoad do in Unity?

Which of the following best describes the purpose of DontDestroyOnLoad in Unity?

A It prevents a GameObject from being destroyed when loading a new scene.

B It disables a GameObject permanently in the current scene.

C It reloads the current scene without destroying any GameObjects.

D It destroys all GameObjects except the one it is called on.

💡 Hint

Think about what happens to GameObjects normally when a new scene loads.

Normally, all GameObjects in a scene are destroyed when a new scene loads. DontDestroyOnLoad keeps the specified GameObject alive across scene loads.

🔧 Debug

advanced

Why does this GameObject duplicate after scene loads?

Look at this code snippet. Why does the GameObject duplicate after loading a new scene multiple times?

Unity

using UnityEngine;
using UnityEngine.SceneManagement;

public class PersistentObject : MonoBehaviour
{
    void Awake()
    {
        DontDestroyOnLoad(gameObject);
    }

    void Start()
    {
        SceneManager.LoadScene("Scene2");
    }
}

A Because Awake is not called when loading a new scene.

B Because DontDestroyOnLoad destroys the object after scene load causing a new one to be created.

C Because SceneManager.LoadScene unloads all objects including those marked DontDestroyOnLoad.

D Because the script does not check if an instance already exists before calling DontDestroyOnLoad.

💡 Hint

Think about what happens if the scene with this script is loaded multiple times.

Each time the scene loads, a new GameObject with this script is created and marked DontDestroyOnLoad, causing duplicates. To avoid this, check if an instance already exists before creating or marking DontDestroyOnLoad.

📝 Syntax

advanced

Identify the syntax error in DontDestroyOnLoad usage

Which option contains a syntax error when trying to use DontDestroyOnLoad?

Unity

using UnityEngine;

public class Example : MonoBehaviour
{
    void Awake()
    {
        // Mark this GameObject to not be destroyed on scene load
        DontDestroyOnLoad(gameObject);
    }
}

A DontDestroyOnLoad(gameObject);

B DontDestroyOnLoad(this);

C DontDestroyOnLoad(gameObject) // missing semicolon

D DontDestroyOnLoad(gameObject); // correct usage

💡 Hint

Check for missing punctuation in the code.

Option C is missing a semicolon at the end of the statement, causing a syntax error.

🚀 Application

expert

How to prevent multiple persistent GameObjects using DontDestroyOnLoad?

You want to create a GameObject that persists across scenes without duplicates. Which code snippet correctly prevents duplicates?

A

void Awake() {
  if (FindObjectsOfType<PersistentObject>().Length > 1) {
    Destroy(gameObject);
  } else {
    DontDestroyOnLoad(gameObject);
  }
}

B

void Awake() {
  DontDestroyOnLoad(gameObject);
}

C

void Awake() {
  if (GameObject.Find("PersistentObject") == null) {
    DontDestroyOnLoad(gameObject);
  }
}

D

void Awake() {
  Destroy(gameObject);
  DontDestroyOnLoad(gameObject);
}

💡 Hint

Think about how to check if another instance already exists before marking DontDestroyOnLoad.

Option A checks if more than one instance exists and destroys the duplicate, ensuring only one persistent GameObject remains.