By this point you should understand the concept of Prefabs at a fundamental level. They are a collection of predefined GameObjects & Components that are re-usable throughout your game. If you don’t know what a Prefab is, we recommend you read the Prefabs page for a more basic introduction.
Prefabs come in very handy when you want to instantiate complicated GameObjects at runtime. The alternative to instantiating Prefabs is to create GameObjects from scratch using code. Instantiating Prefabs has many advantages over the alternative approach:
To illustrate the strength of Prefabs, let’s consider some basic situations where they would come in handy:
This explanation will illustrate the advantages of using a Prefab vs creating objects from code.
First, lets build a brick wall from code:
// JavaScript
function Start () {
for (var y = 0; y < 5; y++) {
for (var x = 0; x < 5; x++) {
var cube = GameObject.CreatePrimitive(PrimitiveType.Cube);
cube.AddComponent.<Rigidbody>();
cube.transform.position = Vector3 (x, y, 0);
}
}
}
// C#
public class Instantiation : MonoBehaviour {
void Start() {
for (int y = 0; y < 5; y++) {
for (int x = 0; x < 5; x++) {
GameObject cube = GameObject.CreatePrimitive(PrimitiveType.Cube);
cube.AddComponent<Rigidbody>();
cube.transform.position = new Vector3(x, y, 0);
}
}
}
}
If you execute that code, you will see an entire brick wall is created when you enter Play mode. There are two lines relevant to the functionality of each individual brick: the CreatePrimitive line, and the AddComponent line. Not so bad right now, but each of our bricks is un-textured. Every additional action to want to perform on the brick, like changing the texture, the friction, or the Rigidbody mass, is an extra line.
If you create a Prefab and perform all your setup before-hand, you use one line of code to perform the creation and setup of each brick. This relieves you from maintaining and changing a lot of code when you decide you want to make changes. With a Prefab, you just make your changes and Play. No code alterations required.
If you’re using a Prefab for each individual brick, this is the code you need to create the wall.
// JavaScript
var brick : Transform;
function Start () {
for (var y = 0; y < 5; y++) {
for (var x = 0; x < 5; x++) {
Instantiate(brick, Vector3 (x, y, 0), Quaternion.identity);
}
}
}
// C#
public Transform brick;
void Start() {
for (int y = 0; y < 5; y++) {
for (int x = 0; x < 5; x++) {
Instantiate(brick, new Vector3(x, y, 0), Quaternion.identity);
}
}
}
This is not only very clean but also very reusable. There is nothing saying we are instantiating a cube or that it must contain a rigidbody. All of this is defined in the Prefab and can be quickly created in the Editor.
Now we only need to create the Prefab, which we do in the Editor. Here’s how:
We’ve created our Brick Prefab, so now we have to attach it to the brick variable in our script. When you select the empty GameObject that contains the script, the Brick variable will be visible in the inspector.
Now drag the “Brick” Prefab from the Project View onto the brick variable in the Inspector. Press Play and you’ll see the wall built using the Prefab.
This is a workflow pattern that can be used over and over again in Unity. In the beginning you might wonder why this is so much better, because the script creating the cube from code is only 2 lines longer.
But because you are using a Prefab now, you can adjust the Prefab in seconds. Want to change the mass of all those instances? Adjust the Rigidbody in the Prefab only once. Want to use a different Material for all the instances? Drag the Material onto the Prefab only once. Want to change friction? Use a different Physic Material in the Prefab’s collider. Want to add a Particle System to all those boxes? Add a child to the Prefab only once.
Here’s how Prefabs fit into this scenario:
While it would be possible to build a rocket GameObject completely from code, adding Components manually and setting properties, it is far easier to instantiate a Prefab. You can instantiate the rocket in just one line of code, no matter how complex the rocket’s Prefab is. After instantiating the Prefab you can also modify any properties of the instantiated object (e.g. you can set the velocity of the rocket’s Rigidbody).
Aside from being easier to use, you can update the prefab later on. So if you are building a rocket, you don’t immediately have to add a Particle trail to it. You can do that later. As soon as you add the trail as a child GameObject to the Prefab, all your instantiated rockets will have particle trails. And lastly, you can quickly tweak the properties of the rocket Prefab in the Inspector, making it far easier to fine-tune your game.
This script shows how to launch a rocket using the Instantiate() function.
// JavaScript
// Require the rocket to be a rigidbody.
// This way we the user can not assign a prefab without rigidbody
var rocket : Rigidbody;
var speed = 10.0;
function FireRocket () {
var rocketClone : Rigidbody = Instantiate(rocket, transform.position, transform.rotation);
rocketClone.velocity = transform.forward * speed;
// You can also acccess other components / scripts of the clone
rocketClone.GetComponent.<MyRocketScript>().DoSomething();
}
// Calls the fire method when holding down ctrl or mouse
function Update () {
if (Input.GetButtonDown("Fire1")) {
FireRocket();
}
}
// C#
// Require the rocket to be a rigidbody.
// This way we the user can not assign a prefab without rigidbody
public Rigidbody rocket;
public float speed = 10f;
void FireRocket () {
Rigidbody rocketClone = (Rigidbody) Instantiate(rocket, transform.position, transform.rotation);
rocketClone.velocity = transform.forward * speed;
// You can also acccess other components / scripts of the clone
rocketClone.GetComponent<MyRocketScript>().DoSomething();
}
// Calls the fire method when holding down ctrl or mouse
void Update () {
if (Input.GetButtonDown("Fire1")) {
FireRocket();
}
}
Let’s say you have a fully rigged enemy character who dies. You could simply play a death animation on the character and disable all scripts that usually handle the enemy logic. You probably have to take care of removing several scripts, adding some custom logic to make sure that no one will continue attacking the dead enemy anymore, and other cleanup tasks.
A far better approach is to immediately delete the entire character and replace it with an instantiated wrecked prefab. This gives you a lot of flexibility. You could use a different material for the dead character, attach completely different scripts, spawn a Prefab containing the object broken into many pieces to simulate a shattered enemy, or simply instantiate a Prefab containing a version of the character.
Any of these options can be achieved with a single call to Instantiate(), you just have to hook it up to the right prefab and you’re set!
The important part to remember is that the wreck which you Instantiate() can be made of completely different objects than the original. For example, if you have an airplane, you would model two versions. One where the plane consists of a single GameObject with Mesh Renderer and scripts for airplane physics. By keeping the model in just one GameObject, your game will run faster since you will be able to make the model with less triangles and since it consists of fewer objects it will render faster than using many small parts. Also while your plane is happily flying around there is no reason to have it in separate parts.
To build a wrecked airplane Prefab, the typical steps are:
The following example shows how these steps are modelled in code.
// JavaScript
var wreck : GameObject;
// As an example, we turn the game object into a wreck after 3 seconds automatically
function Start () {
yield WaitForSeconds(3);
KillSelf();
}
// Calls the fire method when holding down ctrl or mouse
function KillSelf () {
// Instantiate the wreck game object at the same position we are at
var wreckClone = Instantiate(wreck, transform.position, transform.rotation);
// Sometimes we need to carry over some variables from this object
// to the wreck
wreckClone.GetComponent.<MyScript>().someVariable = GetComponent.<MyScript>().someVariable;
// Kill ourselves
Destroy(gameObject);
// C#
public GameObject wreck;
// As an example, we turn the game object into a wreck after 3 seconds automatically
IEnumerator Start() {
yield return new WaitForSeconds(3);
KillSelf();
}
// Calls the fire method when holding down ctrl or mouse
void KillSelf () {
// Instantiate the wreck game object at the same position we are at
GameObject wreckClone = (GameObject) Instantiate(wreck, transform.position, transform.rotation);
// Sometimes we need to carry over some variables from this object
// to the wreck
wreckClone.GetComponent<MyScript>().someVariable = GetComponent<MyScript>().someVariable;
// Kill ourselves
Destroy(gameObject);
}
}
Lets say you want to place a bunch of objects in a grid or circle pattern. Traditionally this would be done by either:
So use Instantiate() with a Prefab instead! We think you get the idea of why Prefabs are so useful in these scenarios. Here’s the code necessary for these scenarios:
// JavaScript
// Instantiates a prefab in a circle
var prefab : GameObject;
var numberOfObjects = 20;
var radius = 5;
function Start () {
for (var i = 0; i < numberOfObjects; i++) {
var angle = i * Mathf.PI * 2 / numberOfObjects;
var pos = Vector3 (Mathf.Cos(angle), 0, Mathf.Sin(angle)) * radius;
Instantiate(prefab, pos, Quaternion.identity);
}
}
// C#
// Instantiates a prefab in a circle
public GameObject prefab;
public int numberOfObjects = 20;
public float radius = 5f;
void Start() {
for (int i = 0; i < numberOfObjects; i++) {
float angle = i * Mathf.PI * 2 / numberOfObjects;
Vector3 pos = new Vector3(Mathf.Cos(angle), 0, Mathf.Sin(angle)) * radius;
Instantiate(prefab, pos, Quaternion.identity);
}
}
// JavaScript
// Instantiates a prefab in a grid
var prefab : GameObject;
var gridX = 5;
var gridY = 5;
var spacing = 2.0;
function Start () {
for (var y = 0; y < gridY; y++) {
for (var x=0;x<gridX;x++) {
var pos = Vector3 (x, 0, y) * spacing;
Instantiate(prefab, pos, Quaternion.identity);
}
}
}
// C#
// Instantiates a prefab in a grid
public GameObject prefab;
public float gridX = 5f;
public float gridY = 5f;
public float spacing = 2f;
void Start() {
for (int y = 0; y < gridY; y++) {
for (int x = 0; x < gridX; x++) {
Vector3 pos = new Vector3(x, 0, y) * spacing;
Instantiate(prefab, pos, Quaternion.identity);
}
}
}