Addressing 'Transform child out of bounds'

Question

I'm going to set the child GameObject's SetActive to true when the parent GameObject is triggered.

Like this picture, BallIndigo1 is the parent GameoOject and x is the child GameObject which is in SetActive(false).

and I wrote code like this:

void OnTriggerEnter2D(Collider2D col)
{
    if (col.gameObject.activeSelf == true)
    {
        if (col.transform.GetChild(0) != null)
        {
            col.transform.GetChild(0).gameObject.SetActive(true);
        }
        else
        {
            Debug.Log("No child");
        }
    }
}

But the result says:

I don't know why this happened and how to fix it.

Answer 1

You are getting this because the GameObject passed to the OnTriggerEnter2D function col.transform doesn't have a child. You can fix that by checking if col.transform.childCount > 0 before calling col.transform.GetChild(0).

void OnTriggerEnter2D(Collider2D col)
{
    if (col.gameObject.activeSelf == true)
    {
        if (col.transform.childCount > 0 && col.transform.GetChild(0) != null)
        {
            col.transform.GetChild(0).gameObject.SetActive(true);
        }
        else
        {
            Debug.Log("No child");
        }
    }
}

---

If you are 100% sure that this Object has a child then there is another GameObject that is being detected that doesn't have a child. You must filter this GameObject out by tag or layer before calling col.transform.GetChild(0). Create a tag named "Ball" set the Objects you want to detect to this tag. Make sure that the this "Ball" object has a child. The code below should check for that tag and should get ride of that error.

void OnTriggerEnter2D(Collider2D col)
{
    if (col.CompareTag("Ball"))
    {
        if (col.gameObject.activeSelf == true)
        {
            if (col.transform.GetChild(0) != null)
            {
                col.transform.GetChild(0).gameObject.SetActive(true);
            }
            else
            {
                Debug.Log("No child");
            }
        }
    }
}