CODEWITHSUNDEEP
c#unity-game-engine
TommySun
TommySun

Reputation: 57

A question regarding Initializing gameobject in Unity

I'm learning unity3d and c# right now with c++ and c knowledge. However, I'm confused with this line of code. 

private Gameobject cubePrelab;

This is a simple line of code which "defines the object that we want to spawn" according to the lecturer. Then he immediately do things like:

Instantiate(cubePreLab, ...,...)

which clones the object according to the documentation online. I'm confused about the first line of code which it seems like we are just defining an object without actually initializing it. However, the result is with these two line of code, we can actually create a box on the screen but I'm confused why it is a box instead of maybe a trangle.

Upvotes: 1

Views: 528

Answers (1)

Ben Rubin
Ben Rubin

Reputation: 7341

I suggest you read about Unity Prefabs

Since you're new to Unity, I assume you've started off by putting a few objects -- such as a cube -- into your scene right? The Unity Editor makes it easy to put objects into your scene while you're designing your game, but what if you wanted to dynamically add objects into your scene while you're playing your game?

For example, imagine that you created a scene that has a cannon in it, and every time the player hits the Space key, you want to fire a cannonball. When you create your Scene in the Unity editor, you put your cannon in your scene, but how do you add cannonballs while you're playing the game?

You could have a bunch of code that creates a cannonball from scratch every time you fire one, but that's a very time consuming and error-prone way of doing it. This is where prefabs come in. A prefab is like a blueprint for an object that you're going to add to your scene later. So a cannonball prefab would be an object that you design in the Unity Editor just like any other Unity object that you're adding to your scene. You could assign its size, its material, its color, its attack power, and so on through the Unity Editor (no code needed).

First you would create a prefab in the Unity Editor for your cannonball.

After you create a cannonball prefab, you would add a property on your Cannon class such as public GameObject cannonballPrefab, and you'd drag your cannonball prefab from the Unity editor into the "Cannonball Prefab" property of the Cannonball component on your cannon object in the Unity Inspector. So if you only look at the C# code, it looks like the cannonballPrefab field is never getting initialized. However, you are initializing it by dragging a prefab into it in the Unity Editor. To reference your initial question, this is also how Unity knows to create a box and not a triangle in your example. Unity will create an instance of whatever your prefab is.

Then within your Cannon code, you can instantiate an instance of your cannonballPrefab while you're playing the game each time you want to add a cannonball into your scene.

Now when you call Instantiate(cannonballPrefab... Unity adds an instance of your cannonball into your scene. Then you'd probably do some additional initialization by assigning it an initial position, an initial speed, an initial direction, and so on.

Also, like Pac0 said, the tutorial probably has public GameObject cubePrefab (not private) so that you can drag a reference into it from the Unity Editor. Alternatively you could keep it private and add the [SerializeField] attribute to it like below. Unity won't let you assign a private field from the editor unless it has the [SerializeField] attribute on it.

[SerializeField]
private GameObject cubePrefab;

Upvotes: 2

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