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Keep constant number of prefabs

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This should be fairly trivial and I don't know what's wrong with my script. I seem to have trouble understanding how to send http://messages.My gamemanager script keeps track of the number of prefabs and has two functions that are called when a prefab is created/destroyed. I checked that both CountPlatformsUp() and CountPlatformsDown() are called, but my "platforms" variable doesn't keep track and once destroyed platforms are not spawned in Update().

Why?

From the prefab:

function Start () {
    gameManagerObject.GetComponent(_gameManagerScript).CountPlatformsUp();
}

function OnDisable() {
    gameManagerObject.GetComponent(_gameManagerScript).CountPlatformsDown();
}

The gamemanager:

var platformPrefab : GameObject;
var spawnAreaObject : GameObject;

private var spawnAreaTransform;
private var platforms : int = 0;

function Start () {
    spawnAreaTransform  = spawnAreaObject.GetComponent(Transform);
}

function Update () {
    if (platforms <= 20) {
       SpawnPlatform();
    }
}

function CountPlatformsUp () {
    platforms = platforms + 1; 
}

function CountPlatformsDown () {
    platforms = platforms - 1;
}

function SpawnPlatform() {
    var targetPos : Vector3 = Vector3(Random.value * spawnAreaTransform.position.x, Random.value * spawnAreaTransform.position.y, 1.434096);
    Instantiate(platformPrefab, targetPos, Quaternion.identity);
    //platforms = platforms + 1;
}
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asked Jan 21 '12 at 01:23 AM

Nicolinux gravatar image

Nicolinux
51 ● 4 ● 6 ● 7

aldonaletto already gives you a better solution for your problem, but your original way have some problems:

  • If you use OnDisable, you should use OnEnable as counterpart.
  • it seems your platform script have a public variable called "gameManagerObject" . Do you assign the gamemanager object somewhere? Esp. for new created platforms? Note that you can't assign objects from the scene to variables of prefabs.
  • The gameManagerObject variable should be of type "_gameManagerScript" so you avoid the GetComponent calls.
  • A better way would be to make the GameManager a singleton by holding a public static reference to the manager object.

In the "_gameManagerScript.js" script:

static var instance : _gameManagerScript;
function Awake()
{
    instance = this;
}

In your platform script:

function OnEnable () {
    _gameManagerScript.instance.CountPlatformsUp();
}

function OnDisable () {
    _gameManagerScript.instance.CountPlatformsDown();
}
Jan 21 '12 at 05:31 AM Bunny83

Many thanks for the suggestions. To my defense - I am coding a quick prototype, thus the messy coding. Should have mentioned it. I'd like to understand why the "if (platforms <= 20)" does not get called in Update(). Any ideas?

  • I was using OnDisable because Unity lacks OnDestroy(). But you are right, OnEnable would be better especially if I were to reuse objects instead of instantiating new ones.
  • Both the gamemanager and the platforms are prefabs and I assigned a reference from the gamemanager to the platform prefab.
  • You are right, thanks.
  • Good idea with the singleton. I am aware of the pattern but still new to Unity.
Jan 21 '12 at 10:17 AM Nicolinux
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Is the game manager script called "_gamemanagerScript.js"? You should pass the script name without quotes or extension to GetComponent - if the name is "GameManagerScript.js", use GetComponent(GetManagerScript).

Anyway, there's a good method to keep track of the current population of platforms: create an empty object, call it "Platforms", reset its position and rotation and assign the script below to it. Whenever a new platform is created, it's childed to the Platforms object - this way you can just check childCount to know how many platforms are alive (Unity always updates the childCount when a child is added or destroyed). 

var platformPrefab : GameObject;
var spawnAreaObject : GameObject;

private var spawnAreaTransform;

function Start () {
    spawnAreaTransform  = spawnAreaObject.transform; // get transform directly
}

function Update () {
    if (transform.childCount
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answered Jan 21 '12 at 02:37 AM

aldonaletto gravatar image

aldonaletto
41.5k ● 16 ● 42 ● 197

Very cool. Thanks. Will do that. I wonder though why my initial and messy script wasn't working correctly.

Jan 21 '12 at 10:19 AM Nicolinux
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asked: Jan 21 '12 at 01:23 AM

Seen: 631 times

Last Updated: Jan 21 '12 at 07:09 PM

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