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Get a GameObject from a component

I want to get a list of GameObjects that contain this script named Alpha

I then destroy that script on all those Game Objects, but want to keep the list with the Game Objects.

I do it now by Having a list of

 Alpha[] aList = GetComponentsInChildren<Alpha>();

 // Destroy scripts here.
 foreach(Alpha a in aList)
    Destroy(a);

If I didn't destroy the scripts I know I could do

 a.gameObject

However I do have to Destroy these scripts then I want to keep pointing to the GameObject. I tried things like this but failed to compile.

 GameObject[] list;
 
 list = GetComponentsInChildren<Alpha>() as GameObject;

I would rather not have to search through the components twice nor would I like to copy the array before destroying.

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asked Mar 15, 2013 at 10:06 AM

NinjaSu gravatar image

NinjaSu
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1 answer: sort voted first

I came up with this:

 List<GameObject> list = new List<GameObject>();
 
 foreach( Alpha a in GetComponentsInChildren<Alpha>() ) {
    list.Add( a.gameObject );
    Destroy(a);
 }

Basically, I see no major difference between array and List; anything you can do with an array, you can do it with a List. If you insist on using an array, then convert the List to array by adding this line:

 GameObject [] objectList = list.ToArray();
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answered Mar 15, 2013 at 10:29 AM

Chronos-L gravatar image

Chronos-L
4.8k 28 29 46

That is some (n^(numberOfChildren)) * n problem you have created there. Bad idea!

Mar 15, 2013 at 11:45 AM NinjaSu

I don't see any problem with that. Where's the (n^numberOfChildren)*n) complexity? How do you even get the (n^numberOfChildren)*n)?

If you are talking about the foreach(), I insists that you to read on how foreach() works.

My script ##

     void Start () {
         List<GameObject> list = new List<GameObject>();
         
         int i = 0;
         foreach( Collider c in GetComponentsInChildren<Collider>() ) {
             Debug.Log( (i++).ToString() );
             list.Add(c.gameObject);
             Destroy(c);    
         }
         
         i = 0;
         foreach( GameObject g in list ) {
             g.name = (i++).ToString();
         }
     }

I am very sure that I have a O(n) operation here in deleting the component (in my script, a collider). Had I have a O((n^x)*n), my child gameObject will not be named from { 0, ...., n-1 }; when I ran the code, my child gameObject no longer have a collider, and they are named from { 0, ..., n-1 }. So, I am certain that my code is O(n), not O((n^x)*n).

Mar 16, 2013 at 12:57 AM Chronos-L

I suggest you read on how GetComponentsInChildren works.

You are looping n^2 best case, since you are iterating with the foreach as well as getting the components in the children every time the loop comes around.

I also suggest you learn to read better before claiming I posted the same question twice on my other post.

Mar 16, 2013 at 04:44 AM NinjaSu

I made a mistake on your second question, and I apologize for not reading the question carefully and making false accuse.

From my understanding, in a foreach loop, a enumerator is created from the Collections used in the foreach loop at the start of the loop. Then, the enumerator is used to iterate through the whole Collections.

In this case, the foreach() is getting its enumerator from a anonymous Component[] return by the GetComponentsInChildren<>() when the loop starts. So, GetComponentsInChildren<>() is called only once at the start of the foreach() loop.

To backup my point, I wrote the following script

 using UnityEngine;
 using System.Collections;
 
 public class CheckArray : MonoBehaviour {
     
     private int count = 0;
     
     // Use this for initialization
     void Start () {
         foreach( int val in GenerateArray() ) {
             Debug.Log(val);    
         }
     }
     
     int[] GenerateArray() {
         Debug.Log("Generate : " + (count++).ToString() );
         return new int[]{ 2, 4, 6, 8, 10, 12 };    
     }
 }
 

And this is my result:

alt text

If it is a O(n*n) as what you have implied on what is happening in the loop, then I will get 'Generate: 0' up to 'Generate: 5' for calling GenerateArray() in every iteration of the foreach .

screenshot.19.png (24.5 kB)
Mar 16, 2013 at 05:42 AM Chronos-L
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asked: Mar 15, 2013 at 10:06 AM

Seen: 1027 times

Last Updated: Mar 16, 2013 at 12:36 PM