Prefabs and reusable objects in Unity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this prefab instantiation code?

Consider the following Unity C# script snippet that instantiates a prefab multiple times:

public GameObject enemyPrefab;

void Start() {
    for (int i = 0; i < 3; i++) {
        GameObject enemy = Instantiate(enemyPrefab);
        enemy.name = "Enemy_" + i;
        Debug.Log(enemy.name);
    }
}

What will be printed in the Unity console?

Unity

public GameObject enemyPrefab;

void Start() {
    for (int i = 0; i < 3; i++) {
        GameObject enemy = Instantiate(enemyPrefab);
        enemy.name = "Enemy_" + i;
        Debug.Log(enemy.name);
    }
}

A Enemy_0\nEnemy_1\nEnemy_2

B enemyPrefab\nenemyPrefab\nenemyPrefab

C Enemy_1\nEnemy_2\nEnemy_3

D Enemy_0\nEnemy_0\nEnemy_0

💡 Hint

Look at how the loop index i is used to name each instantiated object.

The loop runs 3 times with i values 0, 1, and 2. Each instantiated prefab is renamed to "Enemy_" plus the current i. So the console logs "Enemy_0", "Enemy_1", and "Enemy_2" in order.

🧠 Conceptual

intermediate

Which statement about prefab instances is true?

In Unity, when you create an instance of a prefab in the scene, which of the following is correct?

A Changes made to one instance automatically update the prefab asset and all other instances.

B Changes made to the prefab asset automatically update all instances in the scene.

C Instances cannot be modified individually once created.

D Prefab instances are completely independent and have no link to the original prefab.

💡 Hint

Think about how prefab assets and instances relate in Unity.

Prefab instances are linked to the prefab asset. When you modify the prefab asset, all instances update automatically. However, changes to an instance do not affect the prefab asset or other instances unless you apply those changes explicitly.

🔧 Debug

advanced

Why does this prefab instantiation code cause a NullReferenceException?

Examine the following Unity C# code snippet:

public GameObject bulletPrefab;

void Shoot() {
    GameObject bullet = Instantiate(bulletPrefab);
    bullet.GetComponent().AddForce(transform.forward * 500);
}

When running, it throws a NullReferenceException at the GetComponent line. What is the most likely cause?

A The <code>AddForce</code> method requires a second parameter specifying the force mode.

B The <code>Rigidbody</code> component is missing from the <code>bulletPrefab</code> prefab.

C The <code>bulletPrefab</code> variable is not assigned in the Inspector, so it is null.

D The <code>transform</code> variable is null in this context.

💡 Hint

Check if the prefab variable is assigned before instantiating.

If bulletPrefab is null (not assigned in the Inspector), then Instantiate returns null, so calling GetComponent on null causes the exception.

📝 Syntax

advanced

Which option correctly instantiates a prefab and sets its parent?

You want to instantiate a prefab and make the new object a child of a specific GameObject called container. Which code snippet is correct?

A GameObject obj = Instantiate(prefab, container.transform, false);

B GameObject obj = Instantiate(prefab, container.transform);

C GameObject obj = Instantiate(prefab, container.transform.position, container.transform.rotation); obj.transform.parent = container.transform;

D GameObject obj = Instantiate(prefab); obj.transform.parent = container.transform;

💡 Hint

Look for the overload of Instantiate that accepts a parent transform and a boolean for world position.

Option A uses the correct Instantiate overload that sets the parent transform and specifies whether to keep world position. This is the recommended way to instantiate and parent in one step.

🚀 Application

expert

How many unique prefab instances exist after this code runs?

Given the following code snippet in Unity:

public GameObject enemyPrefab;

void SpawnEnemies() {
    GameObject[] enemies = new GameObject[5];
    for (int i = 0; i < 5; i++) {
        enemies[i] = Instantiate(enemyPrefab);
    }
    enemies[2] = enemies[0];
}

After SpawnEnemies() finishes, how many unique GameObjects exist in the enemies array?

A 1

B 3

C 5

D 4

💡 Hint

Consider what happens when you assign enemies[2] = enemies[0].

The loop creates 5 unique instances. But then enemies[2] is set to reference the same object as enemies[0], so the array holds 4 unique GameObjects and one duplicate reference.