Help Need - The Thing you want to initiate is Null

Scripting
1

Dear Community,

I receive the “The Thing you want to initiate is Null” Error. I have reviewed several threats but have been stuck for too long and am now looking for help.

What I essentially want to achieve: A box collider runs ahead of my character and when the box collider hits another box collider in a certain position I want to spawn trees from an array of 7 different prefab trees at the position of the collider

Thanks in advance for any help!

using UnityEngine;
using System.Collections;

public class MG1TreeLooper : MonoBehaviour {
   
    public GameObject[] treePrefabs;
    public Transform treePosition;
   
    void Start (){
        treePrefabs = new GameObject[7];
    }
   
    void OnTriggerEnter2D(Collider2D collider) {
        // Vector3 treePosition = new Vector3(treeLooper.GetComponent<Transform>(),0,0);
        Instantiate (treePrefabs[Random.Range (0,6)], treePosition.position, treePosition.rotation);
    }
}
2

Where are you assigning a value to treePrefabs, and treePosition?

3

With respect to the treePrefabs, I am attaching the 7 prefabs manually via the “public” function to the MG1TreeLooper GameObject which carries the script.

For the treePosition, I similarly reattach the MG1TreeLooper GameObject to itself via “public Transform” as this is where I want the trees to spawn.

4

Are you assigning your tree prefabs via inspector? If yes, you are essentially overwriting your populated array from inspector with the empty one in your Start() function:

void Start ()
{
        treePrefabs = new GameObject[7];
}

Also, irrelevant to the question, it is a bad practice to hard code random like this:

treePrefabs[Random.Range (0,6)]

In case you add 100 more prefabs, you will only pick those between 0 and 6. Also, if you reduce your prefab count to 3, you will get exceptions like array out of bounds.

You might want to write random picking like this:

void OnTriggerEnter2D(Collider2D collider)
{
     int randomIndex = Random.Range (0, treePrefabs.Length - 1);
     GameObject prefab = treePrefabs[randomIndex];
     Instantiate (prefab, treePosition.position, treePosition.rotation);
}

Also a bit nitpicking, but naming your variable:

public Transform treePosition;

will probably confuse someone thinking this variable is Vector3, since transform.position returns Vector3. Since you are using it essentially like a spawn point based on your previous snippet, you could rename it into something like:

public Transform spawnPoint;
public Transform target;
public Transform spawnerTransform;

Hope it helps!

5

Thanks a lot for this! I really appreciate the detail and nitpicking to learn about best practice. The code below is now working and the items are instantiated. It seems like I don’t need the Start() function at all. The prefabs don’t exactly show up where I want them to be and are always moved along to the right (along the x-axis) so need to figure out what is going on there.

    public GameObject[] treePrefabs;
    public Transform spawnPoint;

    void OnTriggerEnter2D(Collider2D collider)
    {
        int randomIndex = Random.Range (0, treePrefabs.Length - 1);
        GameObject prefab = treePrefabs[randomIndex];
        Instantiate (prefab, spawnPoint.position, spawnPoint.rotation);
    }
}