How can I Instantiate two new GameObjects at the same time? (Attempting Asteroids style game)

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Hi all,

I haven't been at my computer learning code or game dev in a few months and am just starting again. I am trying to make a game very similar to Asteroids. In 3d but fixed camera from above so basically disregarding the Y Axis at the moment.

I have everything working fine so far such as the rocket stays in middle and can rotate, and fire weapon. The Asteroids for now all come from the top side of the screen, and have some code to randomise the X location and speeds.

When the laser hits the Asteroid I want it to destroy that Asteroid and create two more that are half the size and with a Rotation added of 45/-45 degrees.

I have the code that I thought would work but it is only creating one more and not two. (note: as you'll see I have tried making tempAsteroid2 and even asteroidPrefab2, before this I just had the one which I tried to instantiate twice).

What am I missing? why does this code not make two more appear upon laser collision??

Any help massively appreciated as always. Many thanks:

 public class Asteroid : MonoBehaviour {
 float speed;
 public GameObject asteroidPrefab, asteroidPrefab2;
 public int sizeKey = 2;
 // Use this for initialization
 void Start () {
     if (sizeKey < 1)
     {
         Destroy(this.gameObject);
     }
     transform.position.Set(transform.position.x, 0f, transform.position.y);
     speed = Random.Range(0.5f, 2f);
 }
 
 // Update is called once per frame
 void Update () {
     GetComponent<Rigidbody>().transform.Translate(Vector3.forward * speed * Time.deltaTime);
 }
 
 private void OnTriggerEnter(Collider other)
 {
     if (other.tag == "Laser")
     {
         BreakAsteroidInHalf();
         Destroy(other.gameObject);
     }
 }
 
 void BreakAsteroidInHalf()
 {
     GameObject tempAsteroid = asteroidPrefab;
     tempAsteroid.transform.position = transform.position;
     tempAsteroid.transform.Rotate(0, -45, 0);
     tempAsteroid.transform.localScale *= 0.5f;
     tempAsteroid.GetComponent<Asteroid>().sizeKey -= 1;
     Instantiate(tempAsteroid);
     GameObject tempAsteroid2 = asteroidPrefab2;
     tempAsteroid2.transform.position = transform.position;
     tempAsteroid2.transform.Rotate(0, 45, 0);
     tempAsteroid2.transform.localScale *= 0.5f;
     tempAsteroid2.GetComponent<Asteroid>().sizeKey -= 1;
     Instantiate(tempAsteroid2);
     Destroy(this.gameObject);
     Debug.Log("Asteroid destroyed and replaced by 2 more");
 
 }

Answer 1

Best Answer

Answer by MacDx · Nov 11, 2017 at 01:13 AM

I see 2 issues with your code.

First of all, you are modifying the prefab. You shouldn't be doing that when instantiating objects, since you are basically changing the template from which subsequent objects will be created and that may have unexpected results.

What you need to do to solve this is very simple just combine the Instantiate(tempAsteroid); with the GameObject tempAsteroid line.

 //Instead of having this:
 GameObject tempAsteroid = asteroidPrefab;
 //bla bla
 Instantiate(tempAsteroid);
 //You should have this:
 GameObject tempAsteroid = Instantiate(asteroidPrefab);
 //bla bla
 //And so you would do the same for tempAsteroid2
 //As a side note, you shouldn't be needing two prefabs for this. One should be enough since you're only changing a rotation, but, if it is simpler for you then leave it like that

The second issue (and the one that I think is mainly causing your problem) is that you are placing both the newly instantiated objects in the exact same position and with the exact same scale, this might be making it so you can't see one of them since the other one is on top of it. Have you checked the hierarchy of objects to see if there's really just one object? Try placing them in different positions, with different scales maybe just to be sure.

Hope this helps!

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megabrobro · Nov 11, 2017 at 02:37 AM 0

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Hi there, thanks for the correct line, I checked some of my old projects (when I understood Unity a bit better) and they have it like that also.

One thing, you have mentioned the second issue about the two items being in the same position etc. We'll I did realise that and it was intended. the colliders are set to be just triggers, and they are rotated differently so i figured they would soon separate.

Also very wierdly, in the Heirarchy inside the editor whislt the game is running, I only see the one instance of the asteroid being created.

I'm very tired now so that might have something to do with why im struggling so much, so I'll write back tomorrow morning after ive had another look and if I still cant figure it out.

Thanks again for your help.

Answer 2

Answer by Leonstar0 · Nov 11, 2017 at 01:25 AM

EDIT: Oh, I am dead wrong, see MacDx's comment.

Hmmmm...

GameObject tempAsteriod = Instantiate(/*insert thingos here*/);

Maybe? An asteroid prefab probably isn't a game object.

Ohhhhhh! I see!

public GameObject asteroidPrefab, asteroidPrefab2;

Yah wrote this, but never assigned it to any value! Hah, I see how that would make things even more confusing! Basically you made empty game objects in your code asteriodPrefab, asteriodPrefab2, then later on created tempAsteriod1 and tempAsteriod2, assigning their reference to the empty game objects. Thus... of course nothing is created! The asteroid prefab you want to use isn't a game object, it's this... data-thing, which you feed into the instantiate method to create a game object with the properties of the prefab. ( I think). Does that make sense?

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MacDx · Nov 11, 2017 at 02:08 AM 0

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Ammmm

Thus... of course nothing is created!

No, because he said

I have the code that I thought would work but it is only creating one more and not two.

And also no, to this:

Yah wrote this, but never assigned it to any value! Hah, I see how that would make things even more confusing!

Because he probably assigned the variable through the inspector. And if he didn't he would be getting a null reference error but he isn't (or at least he didn't say so).

So I'm pretty sure you are dead wrong here @Leonstar0

Leonstar0 · Nov 11, 2017 at 02:22 AM 0

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@MaxDx Doh! Forgot that public exposed it in the inspector! Yeppers! Yikes! Well... I discovered a wrong answer! Should I leave it there with an edit to say I'm wrong, or should I delete the answer?

megabrobro · Nov 11, 2017 at 02:34 AM 0

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thank you for the attempt of help regardless. And I now understand how to fix this (i beleive) thanks to the above answer. I'll have a go in the morning and see how I get on . Thanks

How can I Instantiate two new GameObjects at the same time? (Attempting Asteroids style game)

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