how to change gameobject variable to a different gameobject in c#

Question

Hi guys! I thought that this would be relatively simple but I have spent hours trying to figure out how I can change a GameObject variable to another GameObject in C#.

Here is my current code :

 using UnityEngine;
 using System.Collections;
 
 public class infect : MonoBehaviour {
 
     public GameObject replicationClass;
 
     void OnCollisionEnter(Collision collision) {
         if (collision.transform.GetComponent<stats> ().status == 1) {
                         collision.transform.GetComponent<stats> ().status = 2;
 
                         collision.transform.GetComponent<replicate> ().replication =  replicationClass;
                         Destroy (gameObject, (Time.deltaTime * 20));
                 }
         }
 
 }

I am trying to change the replication GameObject of the replication script, to the replicationClass GameObject variable defined on line 6. However all this does is set replication (in the replication script) to null and gives me the

MissingReferenceException: The object of type 'GameObject' has been destroyed but you are still trying to access it. Your script should either check if it is null or you should not destroy the object.

error when I run the program. I am very confused as to why this does not work.

Below is my replication script :

 using UnityEngine;
 using System.Collections;
 
 public class replicate : MonoBehaviour {
 
     public float timeLeft = 30.0f;
     public float requiredTime = 30.0f;
     public GameObject replication;
     public GameObject WorldScript;
 
     void Awake(){
         timeLeft = requiredTime;
     }
 
     void Update()
     {
         timeLeft -= Time.deltaTime;
         if(timeLeft < 0)
         {
             timeLeft = requiredTime;
             Debug.Log (replication);
             if(WorldScript.GetComponent<worldStats>().currentCells < WorldScript.GetComponent<worldStats>().maxCells)
             Instantiate(replication, gameObject.transform.FindChild("spawnPoint").position, transform.rotation);
 
         }
     }
 }

Does anybody know what I'm doing wrong here? Thank you very much for your time and help =) I would appreciate it if all code you showed me was in C#

Answer 1

I am a newbie. But I have had some problem between understanding TYPES.

An easy way for me to get the right one is 2 ways:

Understanding types... While you defined replicationClass correctly, isn't it technically a wrong name...... maybe you should call it replicationObject, because after all this variable you defined as a GameObject. Now, if you have this (infect) script attached to some gameobject on the scene... Then you simply define it different..... lets call it replicationObject instead please.. and use this code in it's place...

  //Defining a parameter
     int a = replicationObject.GetComponent <Infect> ().somevariablethatisinsidetheinfectscript;
     
     //Calling a method
     bool didHeInfectSomeone = replicationObject.GetComponent <Infect> ().IInfectedSomeone ();
     
     
     //and then inside the infect, you can set a method after update that says something like:
     public bool IInfectedSomeone ()
     {
       return myInfectionStatus; // we may have set this to false initially, or whatever.. hopefully you see what I am doing with the script
     }

So hopefully as you can see. When we want to access the Class, we simply access it as part of a component of the actual gameobject in the scene. Because that's all scripts really are.

I am not the best about STATIC scripts. but if you research how to make a Class script STATIC... Then you can access it a little easier. and intead use phrasing like:

 int a = Infect.somevariableIhaveinsideThisScript;
 
 if (Infect.IInfectedSomeone)
 {
  print ("Holy cow, he infected someone");
 }

the 2nd way

to access understanding it... Is using the drag and drop method in the Unity Editor.

As you have your code currently setup... All you have to do is attach the Infect script to "some game object inside the scene". And then inside the UnityEditor for drag in the Object that you added the infect script to.... It's that simple.

But again, when calling it... You will still have to call it as a GetComponent of that object.

For collisions, they are obviously another component of the Gameobject...

 collision.GameObject.GetComponent <Infect> ().variable = 2;

Answer 2

If replicationClass is the object itself than the problem is obvious: you assign the reference to this object to another script and destroy the object then try to Instantiate from that destroyed object. Try changing replicationClass to a prefab reference (probably created from the same object) and it will work.

P.S. You have a lot of GetComponent's in your code, they make the code less readable and most likely less efficient, try using variables to store these references like:

void OnCollisionEnter(Collision collision) {
    stats s = collision.transform.GetComponent();
    if (s.status == 1) {
        s.status = 2;
        collision.transform.GetComponent ().replication = replicationClass;
        Destroy (gameObject, (Time.deltaTime * 20));
    }
}

Also it would be cool changing WorldScript variable type to worldStats since you don't use operation on the object itself, only that script.

how to change gameobject variable to a different gameobject in c#

2 Replies

the 2nd way

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